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Article

Visible-Light-Induced Decarboxylation of Dioxazolones to Phosphinimidic Amides and Ureas

by
Jie Pan
1,
Haocong Li
1,
Kai Sun
1,2,*,
Shi Tang
3 and
Bing Yu
1,*
1
Green Catalysis Center, College of Chemistry, Zhengzhou University, Zhengzhou 450001, China
2
College of Chemistry & Materials Engineering, Huaihua University, Huaihua 418008, China
3
College of Chemistry and Chemical Engineering, Jishou University, Jishou 416000, China
*
Authors to whom correspondence should be addressed.
Molecules 2022, 27(12), 3648; https://doi.org/10.3390/molecules27123648
Submission received: 5 May 2022 / Revised: 2 June 2022 / Accepted: 4 June 2022 / Published: 7 June 2022
(This article belongs to the Special Issue Catalytic Green Reductions and Oxidations)
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Abstract

:
A visible-light-induced external catalyst-free decarboxylation of dioxazolones was realized for the bond formation of N=P and N–C bonds to access phosphinimidic amides and ureas. Various phosphinimidic amides and ureas (47 examples) were synthesized with high yields (up to 98%) by this practical strategy in the presence of the system’s ppm Fe.

Graphical Abstract

1. Introduction

Nowadays, the development of clean, environmentally friendly, and efficient chemical processes has become one of the goals of sustainable chemistry [1,2,3,4]. Visible light, as a safe, abundant, and renewable natural energy source, has promoted many feasible and valuable transformations [5,6,7,8]. Photocatalytic strategies were widely recognized as an attractive “green synthesis pathway” in organic transformations, which are promising from the standpoint of an environmentally friendly and sustainable perspective [9,10,11,12,13,14,15,16,17,18]. Despite the simple operation and mild reaction conditions, a precious metal complex or a synthetically elaborate organic dye is usually required [19,20,21,22]. It is of great significance to develop cleaner and greener photochemical pathways in the external catalyst-free protocol [23,24,25,26,27].
Nitrene intermediates have attracted great interest from chemists, due to their high reactivity [28,29,30,31,32,33,34,35,36]. Nitrene-based transformations allow the direct installation of nitrogen-containing building blocks into molecular backbones to build structurally complex compounds [37,38,39,40]. In the past few decades, a series of nitrene precursors were reported, such as organic azides [41,42], iminoiodinanes [43,44], amide N-O compounds [45,46], dioxazolones [47,48,49,50], and so on. Among them, dioxazolones are highly attractive because of their high activity, stability, convenience, and high coordination ability [51,52,53]. Herein, we present a visible-light-induced strategy to build N=P and N–C bonds for the generation of phosphinimidic amides and ureas from the reaction of dioxazolones and triarylphosphines or secondary amines (Scheme 1). The transformations are realized without any other catalyst or additive at room temperature. The ppm Fe in the reactants, confirmed by ICP-MS, might play an important role in this reaction.

2. Results and Discussion

Optimization of the Reaction Conditions

We commenced our study with the model reaction between 3-phenyl-1,4,2-dioxazol-5-one (1a) and triphenylphosphine (2a) under visible light and N2 atmosphere. The results are shown in Table 1. Initially, the reaction was carried out by employing DCE as the solvent under irradiation of 10 W 430 nm blue LED at room temperature, and the desired product N-(triphenyl-λ5-phosphinylidene)benzamide (3a) could be detected in 11% yield (entry 1). Afterwards, the solvent effect on the yield was investigated (entries 2–8). Different solvents, such as 1,4-dioxane, CH3OH, acetone, CH3CN, DMF, THF, and CH2Cl2, were surveyed, and the reaction exhibited excellent reaction performance in CH2Cl2 to provide the target product in 81% yield (entry 8). Further examination of the wavelengths of LED and substrate ratios showed no more positive results (entries 9–14). Control reactions confirmed that nearly no amidation product 3a was detected at room temperature in the absence of visible light (entry 15). Moreover, when the reaction was carried out in the air, only a trace amount of the product 3a was detected (entry 16). Therefore, the optimized reaction conditions were illustrated as follows: 1a (0.1 mmol); 2a (0.1 mmol); and CH2Cl2 (1 mL) in a N2 atmosphere under the irradiation of 430 nm blue LED (10 W) for 24 h at room temperature (entry 8).
With the optimized conditions in hand, the scope of the organophosphorus compounds and dioxazolones 1 was investigated (Scheme 2). To our delight, various 3-phenyl dioxazolones bearing different electron-donating groups (-CH3, -tBu, and -OCH3) or electron-withdrawing groups (-CF3, -F, -Cl, and -CN) on the phenyl ring at different positions could react smoothly with 2a to produce the desired products (3a–3n) in moderate to excellent yields (42–98%). Among these cases, a slight steric hindrance effect was observed, and para-substituted 3-phenyl dioxazolones (3a–3h, 63–98%) showed higher reaction reactivities than those of ortho-substituted 3-phenyl dioxazolones (3m–3n, 42–47%). Moreover, the desired products 3o and 3p, which contain the skeletons of thiophene and furan, could also be successfully obtained in 43% and 50% of the yields, respectively. Additionally, electron-poor and electron-rich triphenylphosphine derivatives were all applicable to this transformation to access the desired products (3q–3v) in 51–91% yields. In addition, the phosphorus ligand, 1.1′-binaphthyl-2.2′-diphenylphosphine (BINAP), was also a suitable substrate to react with 1a, providing the corresponding product 3w in 51% yield.
Reaction conditions: 1a (0.2 mmol); 2a (0.2 mmol) in solvent (2 mL) at room temperature for 24 h under the irradiation of 10 W 430 nm blue LED. Isolated yields were given.
Then, we expanded the photocatalytic decarboxylation reaction of dioxazolones to the synthesis of unsymmetrical urea compounds (Scheme 3). To our delight, a wide range of 3-phenyl dioxazolones all reacted efficiently with diisopropylamine 4a to furnish the corresponding aryl ureas (5a–5m) in moderate to excellent yields (37–98%). In these cases, 3-phenyl dioxazolones bearing electron-donating groups (-CH3, -tBu, and -OCH3) showed a better reaction efficiency than those of 3-phenyl dioxazolones bearing electron-withdrawing groups (-CF3, -F, -Cl). Moreover, the broad scope of the commercially available secondary amines all reacted smoothly in this transformation, adding to the formation of desired ureas (5n–5v) in good to excellent yields (80–96%). In addition, the primary amine, such as aniline, was also a suitable substrate for reaction with 1a, providing the corresponding product 5w in 52% yield. However, cyclohexylamine (4l) and benzylamine (4m) were not suitable in this transformation to react with 1a to access the corresponding products 5x and 5y. Compared with the previous report [32], our method effectively avoids the harsh conditions of high temperature, showing good sustainability.
To our satisfaction, this method is also suitable for the reaction between 3-(p-tolyl)-1,4,2-dioxazol-5-one 1b and 1,3-diphenylpropane-1,3-dione 6 to give the corresponding amide product in 58% yield (Scheme 4a), which was previously reported in the presence of additional FeCl3 catalyst [29]. To verify the practicability of this synthetic protocol, the gram-scale synthesis of 3a was carried out (for details, see the Supplementary Materials). When the reaction was performed at a 5 mmol scale, the desired product 3a was isolated in 80% yield, indicating that this approach has a good practicability and application prospect (Scheme 4b).
Furthermore, we also evaluated the sensitivity of the reaction of 1a and 2a. Compared with the standard conditions, the changes in concentration, temperature, oxygen level, water level, light intensity, and scale were measured. The yields were measured by 31P NMR and the yield deviation was calculated (for details, see the Supplementary Materials). Among them, light intensity and oxygen levels are important parameters for the reaction. Moreover, this transformation is moderately sensitive to water. Other parameters, such as concentration and temperature, can be regarded as random errors, which have a negligible impact on reaction efficiency (Figure S4, Supplementary Materials).
Next, we calculated the E-factor [54,55] and EcoScale scores [56,57] of the chemical process to evaluate the safety, economic, and ecological properties of the method. The results are summarized in Tables S2–S5, Supplementary Materials. As can be seen, the E-factor is extremely low at 0.38 and 0.82, respectively, and the EcoScale penalty is also low, at 21.5 and 15.5. Both parameters reflect the excellent green chemistry metrics of the protocol.
To understand the mechanism of this transformation, a set of control experiments were performed (Scheme 5). The phosphorylation of 4-methylbenzamide 8 with triphenylphosphine 2a was performed to determine whether the N=P bond was formed through the amide intermediate. However, 4-methyl-N-(triphenyl-λ5-phosphaneylidene) benzamide 3b was not detected (Scheme 5a). Moreover, intermolecular competition experiments of 1a and 8 were conducted, and only product 3a was obtained with 48% yield (Scheme 5b). These results demonstrated that the phosphorylation of dioxazolones was not conducted through amide intermediates. Furthermore, various radical trapping experiments were conducted (Scheme 5c). When (2,2,6,6-tetramethylpiperidine-1-yl)oxidanyl (TEMPO) was added to the model reaction under standard conditions, the reaction was significantly inhibited. The TEMPO-trapped acyl nitrene adducts were detected by high-resolution mass spectrometry (HRMS), with peaks at 277.1922 m/z. Subsequently, when another radical scavenger, 2,6-di-tert-butyl-4-methylphenol (BHT), was subjected under standard conditions, the reaction was also severely suppressed, indicating a radical process in the phosphorylation of dioxazolone with triphenylphosphine. Then, the radical trapping experiments of 1a and 4a were conducted (Scheme 5c). The decreased yields of product 5a indicated that the transformation also involved a radical process.
In 2021, Yu and Bao et al., disclosed that FeCl3 (15 mol%) was required for the imidization of phosphines with dioxazolones under visible light irradiation [29]. While in our case, the transformations worked very well without any other additives. Considering the contamination issues in coupling reactions [58], we reasoned that some iron contamination might be possible in the manufacture of the starting materials. Therefore, the model reaction mixture was analyzed with inductively coupled plasma mass spectrometry (ICP-MS). Consequently, it is found that the Fe content of the reactions for the preparation of phosphinimidic amide (3a) and urea (5a) is approximately 27 ppm and 3 ppm, respectively (for details, see the Supplementary Materials). ICP-MS experiments were also performed on the starting materials of the model reactions (dioxazolone, PPh3, and amine), and the results showed that the iron contents of the dioxazolone, PPh3, and amine were 123 ppm, 420 ppm, and 0.9 ppm, respectively (for details, see the Supplementary Materials). It is reasoned that iron contamination issues in commercial chemicals are unavoidable during the production and transportation processes. When additional iron catalyst FeCl3 (5 mol%) was added to the model reaction under standard conditions, the reaction time was shortened and the yield was increased. These results confirmed that this reaction could be facilitated by iron catalysis (for details, see the Supplementary Materials). These results suggest that, although it is not a real transition-meta-free system, it is still a synthetically useful procedure for the synthesis of phosphinimidic amides and ureas, especially from an industrial chemistry standpoint.
Based on these control experiments and previous literature reports, a plausible reaction pathway is proposed in Scheme 6. Initially, the N atom of dioxazolones 1 coordinates with the Fe center to form complex B, which is excited by visible light to generate the highly active iron-aminyl radical C with the release of CO2. Subsequently, radical C reacts with triphenylphosphine 2a to form the complex D, followed by a reduction and elimination process to obtain product 3. On the other hand, intermediate C underwent Curtius rearrangement to form intermediate E, which further reacts with secondary amines 4 to obtain product 5.

3. Experimental Section

3.1. General Information

All nuclear magnetic resonance (NMR) spectra were recorded on a Bruker Avance 400 MHz in CDCl3 at room temperature (20 ± 3 °C), by using tetramethylsilane as the internal standard. High-resolution mass spectra (HRMS) were conducted on a 3000-mass spectrometer, using Waters Q-Tof MS/MS system with the ESI technique.
Photochemical reactions were carried out under visible light irradiation by a blue LED at 25 °C. The RLH-18 8-position Photo Reaction System manufactured by Beijing Roger Tech Ltd. was used in this system (Figure S1, Supplementary Materials). Eight 10 W blue LEDs were equipped in this photochemical reactor. The wavelength for blue LED is 430 nm, peak width at half-height is 18.4 nm (Figure S2, Supplementary Materials). The distance from the light source to the irradiation vessel was approximately 15 mm.

3.2. General Experimental Procedures for the Synthesis of (3a–3w)

In a 25 mL reaction tube, dioxazolones 1 (0.2 mmol, 1.0 equiv), organic phosphine substrate 2 (0.2 mmol, 1.0 equiv) in 1 mL CH2Cl2 were allowed to stir with irradiation of 10 W blue LED under N2 atmosphere at room temperature for 24 h. After the reaction, the solvent was evaporated under vacuum, and the residue was purified by column chromatography on silica gel to afford the desired products 3a–3w.
N-(triphenyl-λ5-phosphanylidene)benzamide (3a):
White solid (59.7 mg, 78%). 1H NMR (400 MHz, Chloroform-d) δ 8.45–8.38 (m, 2H), 7.94–7.85 (m, 6H), 7.62–7.55 (m, 3H), 7.54–7.41 (m, 9H); 13C NMR (101 MHz, Chloroform-d) δ 176.3 (d, JC-P = 8.0 Hz), 138.7 (d, JC-P = 20.6 Hz), 133.2 (d, JC-P = 10.0 Hz), 132.3 (d, JC-P = 2.9 Hz), 130.7, 129.6 (d, JC-P = 2.6 Hz), 128.7 (d, JC-P = 12.4 Hz), 128.4 (d, JC-P = 99.7 Hz), 127.7; 31P NMR (162 MHz, Chloroform-d) δ 20.71;
4-methyl-N-(triphenyl-λ5-phosphanylidene)benzamide (3b):
White solid (69.0 mg, 87%). 1H NMR (400 MHz, Chloroform-d) δ 8.30 (d, J = 8.2 Hz, 2H), 7.92–7.85 (m, 6H), 7.62–7.55 (m, 3H), 7.53–7.47 (m, 6H), 7.24 (d, J = 7.9 Hz, 2H), 2.42 (s, 3H); 13C NMR (101 MHz, Chloroform-d) δ 176.5 (d, JC-P = 8.1 Hz), 140.9, 135.9 (d, JC-P = 20.5 Hz), 133.2 (d, JC-P = 9.7 Hz), 132.2 (d, JC-P = 2.9 Hz), 129.6 (d, JC-P = 2.6 Hz), 128.7 (d, JC-P = 12.1 Hz), 128.5 (d, JC-P = 99.6 Hz), 128.4, 21.6; 31P NMR (162 MHz, Chloroform-d) δ 20.47;
4-(tert-butyl)-N-(triphenyl-λ5-phosphanylidene)benzamide (3c):
White solid (55.0 mg, 63%). 1H NMR (400 MHz, Chloroform-d) δ 8.33 (d, J = 8.5 Hz, 2H), 7.92–7.84 (m, 6H), 7.61–7.55 (m, 3H), 7.53–7.45 (m, 8H), 1.38 (s, 9H); 13C NMR (101 MHz, Chloroform-d) δ 176.4 (d, JC-P = 8.1 Hz), 153.9, 136.0 (d, JC-P = 20.5 Hz), 133.2 (d, JC-P = 10.1 Hz), 132.2 (d, JC-P = 2.9 Hz), 129.4 (d, JC-P = 2.6 Hz), 128.7 (d, JC-P = 12.4 Hz), 128.5 (d, JC-P = 99.3 Hz), 124.6, 34.9, 31.4; 31P NMR (162 MHz, Chloroform-d) δ 20.24;
4-methoxy-N-(triphenyl-λ5-phosphanylidene)benzamide (3d):
White solid (79 mg, 96%). 1H NMR (400 MHz, Chloroform-d) δ 8.35 (d, J = 8.8 Hz, 2H), 7.91–7.84 (m, 6H), 7.60–7.54 (m, 3H), 7.52–7.46 (m, 6H), 6.94 (d, J = 8.8 Hz, 2H), 3.85 (s, 3H); 13C NMR (101 MHz, Chloroform-d) δ 176.1 (d, JC-P = 7.8 Hz), 161.8, 133.2 (d, JC-P = 9.9 Hz), 132.2 (d, JC-P = 2.9 Hz), 131.5, 131.4 (d, JC-P = 2.5 Hz), 128.7 (d, JC-P = 12.2 Hz), 128.5 (d, JC-P = 99.6 Hz), 112.8, 55.3; 31P NMR (162 MHz, Chloroform-d) δ 20.30;
4-(trifluoromethyl)-N-(triphenyl-λ5-phosphanylidene)benzamide (3e):
White solid (87.6 mg, 94%). 1H NMR (400 MHz, Chloroform-d) δ 8.49 (d, J = 8.1 Hz, 2H), 7.91–7.84 (m, 6H), 7.69 (d, J = 8.1 Hz, 2H), 7.64–7.57 (m, 3H), 7.56–7.49 (m, 6H); 13C NMR (101 MHz, Chloroform-d) δ 174.8 (d, JC-P = 7.7 Hz), 142.0 (d, JC-P = 21.0 Hz), 133.2 (d, JC-P = 10.3 Hz), 132.5 (d, JC-P = 2.9 Hz), 132.2 (q, JC-F = 32.0 Hz), 129.8 (d, JC-P = 2.5 Hz), 128.8 (d, JC-P = 12.4 Hz), 127.9 (d, JC-P = 99.7 Hz), 124.7 (q, JC-F = 3.8 Hz), 124.3 (q, JC-F = 272.4 Hz); 31P NMR (162 MHz, Chloroform-d) δ 21.40; 19F NMR (376 MHz, Chloroform-d) δ −62.47;
4-fluoro-N-(triphenyl-λ5-phosphanylidene)benzamide (3f):
White solid (57.5 mg, 73%). 1H NMR (400 MHz, Chloroform-d) δ 8.38 (dd, J = 8.7, 5.9 Hz, 2H), 7.90–7.82 (m, 6H), 7.61–7.56 (m, 3H), 7.55–7.46 (m, 6H), 7.08 (t, J = 8.8 Hz, 2H); 13C NMR (101 MHz, Chloroform-d) δ 175.3 (d, JC-P = 8.0 Hz), 164.7 (d, JC-F = 249.4 Hz), 134.9 (d, JC-P = 20.1 Hz), 133.2 (d, JC-P = 10.1 Hz), 132.3 (d, JC-P = 2.9 Hz), 131.8 (dd, JC-F = 8.9, JC-P = 2.3 Hz), 128.7 (d, JC-P = 12.3 Hz), 128.2 (d, JC-P = 99.7 Hz), 114.4 (d, JC-F = 21.4 Hz); 31P NMR (162 MHz, Chloroform-d) δ 20.87; 19F NMR (376 MHz, Chloroform-d) δ −110.66;
4-chloro-N-(triphenyl-λ5-phosphanylidene)benzamide (3g):
White solid (81.8 mg, 98%). 1H NMR (400 MHz, Chloroform-d) δ 8.33 (d, J = 8.5 Hz, 2H), 7.91–7.82 (m, 6H), 7.62–7.55 (m, 3H), 7.54–7.48 (m, 6H), 7.39 (d, J = 8.5 Hz, 2H); 13C NMR (101 MHz, Chloroform-d) δ 175.2 (d, JC-P = 7.9 Hz), 137.2 (d, JC-P = 21.2 Hz), 136.8, 133.2 (d, JC-P = 9.7 Hz), 132.4 (d, JC-P = 2.9 Hz), 131.1 (d, JC-P = 2.3 Hz), 128.8 (d, JC-P = 12.4 Hz), 128.1 (d, JC-P = 99.7 Hz), 127.8; 31P NMR (162 MHz, Chloroform-d) δ 21.05;
4-cyano-N-(triphenyl-λ5-phosphaneylidene)benzamide (3h):
White solid (57.6 mg, 71%), mp 185.5–187.1 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.44 (d, J = 8.1 Hz, 2H), 7.89–7.80 (m, 6H), 7.70 (d, J = 8.3 Hz, 2H), 7.64–7.57 (m, 3H), 7.56–7.49 (m, 6H); 13C NMR (101 MHz, Chloroform-d) δ 174.2 (d, JC-P = 8.1 Hz), 142.8 (d, JC-P = 21.3 Hz), 133.1 (d, JC-P = 9.7 Hz), 132.6 (d, JC-P = 3.0 Hz), 131.6, 130.0 (d, JC-P = 2.3 Hz), 128.9 (d, JC-P = 12.4 Hz), 127.7 (d, JC-P = 99.8 Hz), 119.1, 113.8; 31P NMR (162 MHz, Chloroform-d) δ 21.79. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C26H20N2OP, 407.1308; found, 407.1309;
3-methoxy-N-(triphenyl-λ5-phosphanylidene)benzamide (3i):
White solid (62.4 mg, 76%). 1H NMR (400 MHz, Chloroform-d) δ 8.05 (d, J = 7.6 Hz, 1H), 7.93–7.83 (m, 7H), 7.61–7.55 (m, 3H), 7.54–7.47 (m, 6H), 7.35 (t, J = 7.9 Hz, 1H), 7.06–7.01 (m, 1H), 3.88 (s, 3H); 13C NMR (101 MHz, Chloroform-d) δ 176.1 (d, JC-P = 8.1 Hz), 159.3, 140.2 (d, JC-P = 20.5 Hz), 133.2 (d, JC-P = 9.7 Hz), 132.3 (d, JC-P = 2.9 Hz), 128.7 (d, JC-P = 12.5 Hz), 128.3 (d, JC-P = 99.2 Hz), 122.3 (d, JC-P = 2.6 Hz), 117.4, 113.8 (d, JC-P = 2.9 Hz), 55.4; 31P NMR (162 MHz, Chloroform-d) δ 20.70;
3-(trifluoromethyl)-N-(triphenyl-λ5-phosphanylidene)benzamide (3j):
White solid (65.1 mg, 73%). 1H NMR (400 MHz, Chloroform-d) δ 8.67 (s, 1H), 8.57 (d, J = 7.7 Hz, 1H), 7.92–7.84 (m, 6H), 7.72 (d, J = 8.1 Hz, 1H), 7.64–7.58 (m, 3H), 7.57–7.50 (m, 7H); 13C NMR (101 MHz, Chloroform-d) δ 174.7 (d, JC-P = 7.7 Hz), 139.5 (d, JC-P = 21.2 Hz), 133.2 (d, JC-P = 10.2 Hz), 132.8, 132.4 (d, JC-P = 3.0 Hz), 130.1 (q, JC-F = 32.2 Hz), 128.8 (d, JC-P = 12.4 Hz), 128.2, 128.0 (d, JC-P = 99.8 Hz), 127.1 (q, JC-F = 3.8 Hz), 126.5 (q, JC-F = 3.5 Hz), 123.0 (q, JC-F = 272.2 Hz); 31P NMR (162 MHz, Chloroform-d) δ 21.62; 19F NMR (376 MHz, Chloroform-d) δ −62.33;
3-fluoro-N-(triphenyl-λ5-phosphanylidene)benzamide (3k):
White solid (48.7 mg, 61%), mp 154.6–156.5 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.14 (d, J = 7.7 Hz, 1H), 8.10–8.05 (m, 1H), 7.91–7.82 (m, 6H), 7.63–7.56 (m, 3H), 7.55–7.48 (m, 6H), 7.42–7.34 (m, 1H), 7.19–7.13 (m, 1H); 13C NMR (101 MHz, Chloroform-d) δ 175.0 (d, JC-P = 7.4 Hz), 162.6 (d, JC-F = 244.8 Hz), 141.2 (d, JC-F = 21.3 Hz), 133.2 (d, JC-P = 10.0 Hz), 132.4 (d, JC-F = 2.9 Hz), 129.1 (d, JC-P = 7.7 Hz), 128.8 (d, JC-P = 12.4 Hz), 128.1 (d, JC-P = 99.8 Hz), 125.1 (d, JC-P = 2.8 Hz), 117.5 (d, JC-P = 21.6 Hz), 116.4 (dd, JC-F = 22.2, JC-P = 2.6 Hz); 31P NMR (162 MHz, Chloroform-d) δ 21.13; 19F NMR (376 MHz, Chloroform-d) δ −114.38. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C25H20FNOP, 400.1261; found, 400.1261;
3-chloro-N-(triphenyl-λ5-phosphanylidene)benzamide (3l):
Colorless liquid (56.7 mg, 64%). 1H NMR (400 MHz, Chloroform-d) δ 8.40–8.36 (m, 1H), 8.23 (d, J = 7.8 Hz, 1H), 7.90–7.82 (m, 6H), 7.63–7.57 (m, 3H), 7.55–7.48 (m, 6H), 7.46–7.41 (m, 1H), 7.37–7.32 (m, 1H); 13C NMR (101 MHz, Chloroform-d) δ 174.9 (d, JC-P = 8.0 Hz), 140.6 (d, JC-P = 21.2 Hz), 133.7, 133.2 (d, JC-P = 10.2 Hz), 132.4 (d, JC-P = 2.6 Hz), 130.6, 129.8 (d, JC-P = 2.7 Hz), 129.0, 128.8 (d, JC-P = 12.0 Hz), 128.0 (d, JC-P = 99.8 Hz), 127.6 (d, JC-P = 2.2 Hz); 31P NMR (162 MHz, Chloroform-d) δ 21.40. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C25H20ClNOP, 416.0966; found, 416.0963;
2-fluoro-N-(triphenyl-λ5-phosphanylidene)benzamide (3m):
White solid (37.5 mg, 47%). 1H NMR (400 MHz, Chloroform-d) δ 8.22–8.16 (m, 1H), 7.93–7.84 (m, 6H), 7.61–7.55 (m, 3H), 7.53–7.47 (m, 6H), 7.41–7.34 (m, 1H), 7.18–7.06 (m, 2H); 13C NMR (101 MHz, Chloroform-d) δ 174.1 (dd, JC-P = 7.9 Hz, JC-F = 3.6 Hz), 161.9 (d, JC-F = 255.2 Hz), 133.2 (d, JC-P = 10.1 Hz), 132.4 (dd, JC-P = 2.3 Hz, JC-F = 2.2 Hz), 132.3 (d, JC-P = 2.9 Hz), 131.7 (d, JC-F = 8.8 Hz), 128.7 (d, JC-P = 12.4 Hz), 128.0 (d, JC-P = 99.3 Hz), 127.5 (dd, JC-P = 21.4 Hz, JC-F = 9.9 Hz), 123.3 (d, JC-F = 3.8 Hz), 116.5 (d, JC-F = 23.4 Hz); 31P NMR (162 MHz, Chloroform-d) δ 20.39; 19F NMR (376 MHz, Chloroform-d) δ −111.60;
2-chloro-N-(triphenyl-λ5-phosphanylidene)benzamide (3n):
White solid (35.0 mg, 42%), mp 196.6–197.8 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.43–8.36 (m, 2H), 7.92–7.84 (m, 6H), 7.62–7.56 (m, 3H), 7.54–7.48 (m, 6H), 7.46–7.41 (m, 2H); 13C NMR (101 MHz, Chloroform-d) δ 176.4 (d, JC-P = 8.6 Hz), 138.6 (d, JC-P = 20.6 Hz), 133.2 (d, JC-P = 9.7 Hz), 132.3 (d, JC-P = 2.9 Hz), 130.7, 129.6 (d, JC-P = 2.3 Hz), 128.7 (d, JC-P = 12.3 Hz), 128.4 (d, JC-P = 99.5 Hz), 127.7; 31P NMR (162 MHz, Chloroform-d) δ 20.72. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C25H20ClNOP, 416.0966; found, 416.0969;
N-(triphenyl-λ5-phosphanylidene)thiophene-2-carboxamide (3o):
Brown solid (33.3 mg, 43%). 1H NMR (400 MHz, Chloroform-d) δ 7.89–7.82 (m, 6H), 7.80 (dd, J = 3.6, 1.2 Hz, 1H), 7.62–7.56 (m, 3H), 7.53–7.47 (m, 6H), 7.40 (dd, J = 5.0, 1.2 Hz, 1H), 7.10–7.01 (m, 1H); 13C NMR (101 MHz, Chloroform-d) δ 171.1 (d, JC-P = 7.0 Hz), 145.2 (d, JC-P = 24.3 Hz), 133.2 (d, JC-P = 9.7 Hz), 132.3 (d, JC-P = 2.9 Hz), 130.2 (d, JC-P = 2.8 Hz), 129.6, 128.7 (d, JC-P = 12.4 Hz), 128.1 (d, JC-P = 99.7 Hz), 127.3; 31P NMR (162 MHz, Chloroform-d) δ 19.47;
N-(triphenyl-λ5-phosphanylidene)furan-2-carboxamide (3p):
White solid (37.2 mg, 50%). 1H NMR (400 MHz, Chloroform-d) δ 7.87–7.79 (m, 6H), 7.59–7.53 (m, 3H), 7.51–7.45 (m, 7H), 7.17 (d, J = 3.3 Hz, 1H), 6.44 (dd, J = 3.2, 1.7 Hz, 1H); 13C NMR (101 MHz, Chloroform-d) δ 168.0 (d, JC-P = 6.7 Hz), 152.8 (d, JC-P = 26.0 Hz), 144.0, 133.2 (d, JC-P = 10.1 Hz), 132.4, 128.7 (d, JC-P = 12.4 Hz), 127.9 (d, JC-P = 100.2 Hz), 114.3, 111.3; 31P NMR (162 MHz, Chloroform-d) δ 21.86;
N-(tri-p-tolyl-λ5-phosphanylidene)benzamide (3q):
White solid (77.1 mg, 91%). 1H NMR (400 MHz, Chloroform-d) δ 8.42 (d, J = 7.8 Hz, 2H), 7.79 (dd, J = 12.2, 7.7 Hz, 6H), 7.48–7.41 (m, 3H), 7.32 (dd, J = 8.3, 2.8 Hz, 6H), 2.43 (s, 9H); 13C NMR (101 MHz, Chloroform-d) δ 176.2 (d, JC-P = 8.0 Hz), 142.7 (d, JC-P = 2.9 Hz), 138.9 (d, JC-P = 20.8 Hz), 133.2 (d, JC-P = 10.3 Hz), 130.6, 129.6 (d, JC-P = 2.3 Hz), 129.4 (d, JC-P = 12.9 Hz), 127.6, 125.4 (d, JC-P = 102.0 Hz), 21.7; 31P NMR (162 MHz, Chloroform-d) δ 20.63;
N-(tri-p-methoxyphenyl-λ5-phosphanylidene)benzamide (3r):
White solid (56.7 mg, 60%). 1H NMR (400 MHz, Chloroform-d) δ 8.40–8.34 (m, 2H), 7.78 (dd, J = 11.7, 8.8 Hz, 6H), 7.46–7.38 (m, 3H), 7.00 (dd, J = 8.9, 2.3 Hz, 6H), 3.85 (s, 9H); 13C NMR (101 MHz, Chloroform-d) δ 176.1 (d, JC-P = 7.4 Hz), 162.6 (d, JC-P = 2.9 Hz), 139.0 (d, JC-P = 20.4 Hz), 135.0 (d, JC-P = 11.1 Hz), 130.5, 129.5 (d, JC-P = 2.3 Hz), 127.6, 119.9 (d, JC-P = 106.5 Hz), 114.3 (d, JC-P = 13.3 Hz), 55.4; 31P NMR (162 MHz, Chloroform-d) δ 19.68;
N-(tris(4-fluorophenyl)-λ5-phosphanylidene)benzamide (3s):
White solid (44.2 mg, 51%). 1H NMR (400 MHz, Chloroform-d) δ 8.34–8.29 (m, 2H), 7.90–7.81 (m, 6H), 7.50–7.41 (m, 3H), 7.26–7.19 (m, 6H); 13C NMR (101 MHz, Chloroform-d) δ 176.5 (d, JC-P = 8.1 Hz), 165.4 (dd, JC-F = 255.1 Hz, JC-P = 3.2 Hz), 138.1 (d, JC-P = 20.6 Hz), 135.6 (dd, JC-F = 11.7 Hz, JC-P = 8.8 Hz), 131.0, 129.5 (d, JC-P = 2.7 Hz), 127.8, 123.9 (dd, JC-P = 103.9 Hz, JC-F = 3.3 Hz), 116.4 (dd, JC-F = 21.6 Hz, JC-P = 13.6 Hz); 31P NMR (162 MHz, Chloroform-d) δ 18.98; 19F NMR (376 MHz, Chloroform-d) δ −105.30;
N-(tris(4-chlorophenyl)-λ5-phosphanylidene)benzamide (3t):
White solid (80.5 mg, 83%). 1H NMR (400 MHz, Chloroform-d) δ 8.36–8.30 (m, 2H), 7.79 (dd, J = 12.0, 8.4 Hz, 6H), 7.54–7.47 (m, 7H), 7.43 (dd, J = 8.1, 6.2 Hz, 2H); 13C NMR (101 MHz, Chloroform-d) δ 176.7 (d, JC-P = 8.0 Hz), 139.5 (d, JC-P = 3.6 Hz), 137.9 (d, JC-P = 20.5 Hz), 134.4 (d, JC-P = 11.0 Hz), 131.1, 129.5 (d, JC-P = 2.5 Hz), 129.4 (d, JC-P = 12.8 Hz), 127.8, 126.2 (d, JC-P = 102.0 Hz); 31P NMR (162 MHz, Chloroform-d) δ 19.49;
N-(tris(3-methoxyphenyl)-λ5-phosphaneylidene)benzamide (3u):
White solid (48.5 mg, 52%), mp 146.3–147.7 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.41–8.36 (m, 2H), 7.52–7.47 (m, 3H), 7.46–7.34 (m, 9H), 7.12–7.07 (m, 3H), 3.79 (s, 9H); 13C NMR (101 MHz, Chloroform-d) δ 176.2 (d, JC-P = 7.9 Hz), 159.6 (d, JC-P = 15.4 Hz), 138.7 (d, JC-P = 20.6 Hz), 130.7, 129.9 (d, JC-P = 14.6 Hz), 129.6 (d, JC-P = 99.1 Hz), 129.5 (d, JC-P = 2.4 Hz), 127.7, 125.4 (d, JC-P = 9.7 Hz), 118.4 (d, JC-P = 11.0 Hz), 118.1 (d, JC-P = 2.9 Hz), 55.4; 31P NMR (162 MHz, Chloroform-d) δ 21.38. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C28H27NO4P, 472.1672; found, 472.1677;
N-(diphenyl(p-tolyl)-λ5-phosphanylidene)benzamide (3v):
White solid (71.1 mg, 90%). 1H NMR (400 MHz, Chloroform-d) δ 8.45–8.37 (m, 2H), 7.93–7.85 (m, 4H), 7.81–7.74 (m, 2H), 7.61–7.55 (m, 2H), 7.53–7.42 (m, 7H), 7.32 (dd, J = 8.3, 2.9 Hz, 2H), 2.43 (s, 3H); 13C NMR (101 MHz, Chloroform-d) δ 176.3 (d, JC-P = 8.0 Hz), 142.9 (d, JC-P = 2.9 Hz), 138.7 (d, JC-P = 20.6 Hz), 133.3 (d, JC-P = 10.5 Hz), 133.2 (d, JC-P = 9.5 Hz), 132.2 (d, JC-P = 3.0 Hz), 130.7, 129.6, 129.5 (d, JC-P = 10.0 Hz), 128.7 (d, JC-P = 12.3 Hz), 128.6 (d, JC-P = 99.8 Hz), 127.7, 124.8 (d, JC-P = 101.3 Hz), 21.7; 31P NMR (162 MHz, Chloroform-d) δ 20.67;
N,N’-([1,1′-binaphthalene]-2,2′-diylbis(diphenyl-λ5-phosphaneylylidene))dibenzamide (3w):
White solid (87.7 mg, 51%), mp 184.5–185.8 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.18 (d, J = 7.1 Hz, 4H), 7.78–7.69 (m, 6H), 7.57–7.46 (m, 7H), 7.44–7.29 (m, 13H), 7.28–7.21 (m, 3H), 7.20–7.07 (m, 7H), 6.41 (dd, J = 8.3, 5.0 Hz, 2H); 13C NMR (101 MHz, Chloroform-d) δ 175.9 (d, JC-P = 8.0 Hz), 159.6 (d, JC-P = 2.0 Hz), 138.8 (d, JC-P = 21.2 Hz), 135.1 (d, JC-P = 7.1 Hz), 134.1 (d, JC-P = 2.6 Hz), 133.3 (d, JC-P = 10.5 Hz), 132.9 (d, JC-P = 10.3 Hz), 132.1 (d, JC-P = 3.0 Hz), 131.6 (d, JC-P = 2.4 Hz), 130.4, 129.4 (d, JC-P = 2.7 Hz), 128.5 (d, JC-P = 12.5 Hz), 128.2 (d, JC-P = 12.6 Hz), 127.8 (d, JC-P = 104.7 Hz), 127.50, 127.45, 123.9 (d, JC-P = 11.4 Hz), 121.0 (d, JC-P = 6.8 Hz), 119.2 (d, JC-P = 100.4 Hz); 31P NMR (162 MHz, Chloroform-d) δ 19.95. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C58H43N2O2P2, 861.2794; found, 861.2791.

3.3. General Experimental Procedures for the Synthesis of (5a–5w)

In a 25 mL reaction tube, dioxazolone 1 (0.2 mmol, 1.0 equiv.), and amine 4 (0.4 mmol, 2.0 equiv.) in 1 mL CH3OH were allowed to stir with irradiation of 10 W blue LED at room temperature for 5 h. After the reaction, the solvent was evaporated under vacuum, and the residue was purified by column chromatography on silica gel to afford the desired products 5a–5w.
1,1-diisopropyl-3-phenylurea (5a):
White solid (40.1 mg, 91%). 1H NMR (400 MHz, Chloroform-d) δ 7.39 (dd, J = 8.4, 1.3 Hz, 2H), 7.31–7.26 (m, 2H), 7.06–6.99 (m, 1H), 6.26 (s, 1H), 4.04–3.95 (m, 2H), 1.34 (d, J = 7.0 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 154.6, 139.4, 128.8, 122.6, 119.7, 45.5, 21.5;
1,1-diisopropyl-3-(p-tolyl)urea (5b):
White solid (44.9 mg, 96%). 1H NMR (400 MHz, Chloroform-d) δ 7.27 (d, J = 8.3 Hz, 2H), 7.09 (d, J = 8.4 Hz, 2H), 6.18 (s, 1H), 4.04–3.94 (m, 2H), 2.30 (s, 3H), 1.33 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 154.8, 136.8, 132.1, 129.3, 119.9, 45.4, 21.5, 20.7;
3-(4-(tert-butyl)phenyl)-1,1-diisopropylurea (5c):
White solid (49.1 mg, 89%), mp 115.1–116.7 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.33–7.29 (m, 4H), 6.17 (s, 1H), 4.05–3.96 (m, 2H), 1.34 (d, J = 6.9 Hz, 12H); 1.31 (s, 9H); 13C NMR (101 MHz, Chloroform-d) δ 154.9, 145.6, 136.7, 125.7, 119.7, 45.4, 34.2, 31.4, 21.6. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C17H29N2O, 277.2274; found, 277.2284;
1,1-diisopropyl-3-(4-methoxyphenyl)urea (5d):
White solid (49.0 mg, 98%). 1H NMR (400 MHz, Chloroform-d) δ 7.27 (d, J = 8.9 Hz, 2H), 6.83 (d, J = 9.0 Hz, 2H), 6.13 (s, 1H), 4.01–3.92 (m, 2H), 3.77 (s, 3H), 1.32 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 155.5, 155.1, 132.5, 122.0, 114.1, 55.5, 45.4, 21.5;
1,1-diisopropyl-3-(4-(trifluoromethyl)phenyl)urea (5e):
White solid (44.2 mg, 79%), mp 151.9–153.1 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.57–7.46 (m, 4H), 6.43 (s, 1H), 4.07–3.92 (m, 2H), 1.35 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 154.0, 142.6, 126.1 (q, JC-F = 3.8 Hz), 124.4 (q, JC-F = 271.1 Hz), 124.2 (q, JC-F = 32.7 Hz), 118.9, 45.7, 21.5; 19F NMR (376 MHz, Chloroform-d) δ −61.81; HRMS (ESI-TOF) m/z: [M + H]+ calcd for C14H20F3N2O, 289.1522; found, 289.1534;
3-(4-fluorophenyl)-1,1-diisopropylurea (5f):
White solid (36.7 mg, 77%), mp 134.5–135.7 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.35–7.27 (m, 2H), 6.94 (t, J = 8.6 Hz, 2H), 6.31 (s, 1H), 4.03–3.86 (m, 2H), 1.30 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 158.6 (d, JC-F = 241.2 Hz), 154.8, 135.4 (d, JC-F = 2.9 Hz), 121.8 (d, JC-F = 7.9 Hz), 115.2 (d, JC-F = 22.1 Hz), 45.6, 21.4; 19F NMR (376 MHz, Chloroform-d) δ -120.90; HRMS (ESI-TOF) m/z: [M + H]+ calcd for C13H20FN2O, 239.1554; found, 239.1567;
3-(4-chlorophenyl)-1,1-diisopropylurea (5g):
White solid (49.8 mg, 98%). 1H NMR (400 MHz, Chloroform-d) δ 7.32 (d, J = 8.9 Hz, 2H), 7.22 (d, J = 8.8 Hz, 2H), 6.29 (s, 1H), 4.03–3.90 (m, 2H), 1.32 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 154.4, 138.0, 128.7, 127.4, 121.0, 45.6, 21.5;
1,1-diisopropyl-3-(3-methoxyphenyl)urea (5h):
White solid (43.6 mg, 87%). 1H NMR (400 MHz, Chloroform-d) δ 7.20–7.14 (m, 2H), 6.85 (dd, J = 8.0, 1.2 Hz, 1H), 6.57 (dd, J = 8.2, 1.7 Hz, 1H), 6.27 (s, 1H), 4.05–3.95 (m, 2H), 3.81 (s, 3H), 1.33 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 160.2, 154.5, 140.7, 129.4, 111.7, 108.6, 105.1, 55.3, 45.4, 21.5;
1,1-diisopropyl-3-(3-(trifluoromethyl)phenyl)urea (5i):
White solid (21.3 mg, 37%), mp 151.2–152.7 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.67 (s, 1H), 7.62–7.55 (m, 1H), 7.39 (t, J = 7.9 Hz, 1H), 7.29–7.25 (m, 1H), 6.37 (s, 1H), 4.07–3.94 (m, 2H), 1.36 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 154.2, 139.9, 131.2 (q, JC-F = 271.6 Hz), 129.3, 122.7, 119.1 (q, JC-F = 3.7 Hz), 116.1 (q, JC-F = 4.0 Hz), 45.7, 21.5; 19F NMR (376 MHz, Chloroform-d) δ -62.64. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C14H20F3N2O, 289.1522; found, 289.1536;
3-(3-fluorophenyl)-1,1-diisopropylurea (5j):
White solid (23.9 mg, 50%), mp 118.5–119.8 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.40–7.32 (m, 1H), 7.23–7.14 (m, 1H), 7.00 (dd, J = 8.3, 2.1 Hz, 1H), 6.72–6.64 (m, 1H), 6.39 (s, 1H), 4.03–3.89 (m, 2H), 1.32 (d, J = 6.6 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 163.2 (d, JC-F = 243.5 Hz), 154.2, 141.1 (d, JC-F = 11.2 Hz), 129.7 (d, JC-F = 9.6 Hz), 114.7 (d, JC-F = 2.9 Hz), 109.0 (d, JC-F = 21.3 Hz), 106.9 (d, JC-F = 26.4 Hz), 45.6, 21.5; 19F NMR (376 MHz, Chloroform-d) δ -112.35. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C13H20FN2O, 239.1554; found, 239.1564;
1,1-diisopropyl-3-(o-tolyl)urea (5k):
White solid (43.0 mg, 92%), mp 136.8–138.7 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.77 (dd, J = 8.1, 1.2 Hz, 1H), 7.23–7.14 (m, 2H), 7.04–6.96 (m, 1H), 6.07 (s, 1H), 4.11–3.99 (m, 2H), 2.28 (s, 3H), 1.36 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 154.8, 137.6, 130.3, 127.6, 126.7, 123.2, 122.3, 45.4, 21.5, 18.3. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C14H23N2O, 235.1805; found, 235.1816;
3-(2-fluorophenyl)-1,1-diisopropylurea (5l):
White solid (40.0 mg, 84%), mp 109.1–110.7 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.24–8.16 (m, 1H), 7.13–7.02 (m, 2H), 6.99–6.90 (m, 1H), 6.58 (s, 1H), 4.12–4.03 (m, 2H), 1.35 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 154.1, 152.3 (d, JC-F = 239.8 Hz), 128.0 (d, JC-F = 9.5 Hz), 124.5 (d, JC-F = 3.6 Hz), 122.0 (d, JC-F = 7.5 Hz), 121.1, 114.3 (d, JC-F = 19.2 Hz), 45.3, 21.4; 19F NMR (376 MHz, Chloroform-d) δ -133.39. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C13H20FN2O, 239.1554; found, 239.1564;
3-(2-chlorophenyl)-1,1-diisopropylurea (5m):
White solid (49.6 mg, 95%). 1H NMR (400 MHz, Chloroform-d) δ 7.41–7.37 (m, 2H), 7.29 (d, J = 8.6 Hz, 1H), 7.06–6.98 (m, 1H), 6.27 (s, 1H), 4.05–3.95 (m, 2H), 1.34 (d, J = 6.9 Hz, 12H); 13C NMR (101 MHz, Chloroform-d) δ 154.6, 139.4, 128.8, 122.6, 119.7, 45.5, 21.5;
1,1-diethyl-3-phenylurea (5n):
White solid (36.8 mg, 96%). 1H NMR (400 MHz, Chloroform-d) δ 7.43–7.39 (m, 2H), 7.31–7.25 (m, 2H), 7.02 (t, J = 7.3 Hz, 1H), 6.40 (s, 1H), 3.41–3.35 (m, 4H), 1.22 (t, J = 7.1 Hz, 6H); 13C NMR (101 MHz, Chloroform-d) δ 154.7, 139.4, 128.8, 122.8, 119.9, 41.6, 13.9;
3-phenyl-1,1-dipropylurea (5o):
White solid (35 mg, 80%). 1H NMR (400 MHz, Chloroform-d) δ 7.43–7.37 (m, 2H), 7.31–7.25 (m, 2H), 7.06–6.97 (m, 1H), 6.41 (s, 1H), 3.31–3.24 (m, 4H), 1.71–1.61 (m, 4H), 0.96 (t, J = 7.4 Hz, 6H); 13C NMR (101 MHz, Chloroform-d) δ 155.0, 139.4, 128.8, 122.7, 119.8, 49.4, 21.9, 11.4;
1,1-dibutyl-3-phenylurea (5p):
White solid (41.6 mg, 84%). 1H NMR (400 MHz, Chloroform-d) δ 7.44–7.38 (m, 2H), 7.30–7.25 (m, 2H), 7.05–6.99 (m, 1H), 6.38 (s, 1H), 3.34–3.28 (m, 4H), 1.65–1.58 (m, 4H), 1.43–1.34 (m, 4H), 0.98 (t, J = 7.3 Hz, 6H); 13C NMR (101 MHz, Chloroform-d) δ 155.0, 139.4, 128.8, 122.7, 119.7, 47.5, 30.8, 20.2, 13.9;
1-ethyl-3-phenyl-1-propylurea (5q):
Colorless liquid (34.0 mg, 83%), mp 56.3–57.6 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.43–7.37 (m, 2H), 7.31–7.25 (m, 2H), 7.02 (t, J = 7.4 Hz, 1H), 6.39 (s, 1H), 3.42–3.34 (m, 2H), 3.30–3.24 (m, 2H), 1.71–1.61 (m, 2H), 1.22 (t, J = 7.1 Hz, 3H), 0.96 (t, J = 7.4 Hz, 3H); 13C NMR (101 MHz, Chloroform-d) δ 154.9, 139.4, 128.8, 122.7, 119.8, 48.8, 42.1, 22.0, 13.8, 11.4; HRMS (ESI-TOF) m/z: [M + H]+ calcd for C12H19N2O, 207.1492; found, 207.1499;
1-cyclohexyl-1-ethyl-3-phenylurea (5r):
White solid (44.0 mg, 89%), mp 123.5–124.7 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.44–7.39 (m, 2H), 7.31–7.25 (m, 2H), 7.01 (t, J = 7.3 Hz, 1H), 6.41 (s, 1H), 4.14–4.03 (m, 1H), 3.33–3.25 (m, 2H), 1.85–1.76 (m, 4H), 1.72–1.64 (m, 1H), 1.47–1.33 (m, 4H), 1.25 (t, J = 7.2 Hz, 3H), 1.18–1.06 (m, 1H); 13C NMR (101 MHz, Chloroform-d) δ 154.8, 139.5, 128.8, 122.7, 119.9, 54.8, 36.9, 31.5, 26.0, 25.6, 16.1; HRMS (ESI-TOF) m/z: [M + H]+ calcd for C15H23N2O, 247.1805; found, 247.1815;
1,1-dicyclohexyl-3-phenylurea (5s):
White solid (54.0 mg, 90%). 1H NMR (400 MHz, Chloroform-d) δ 7.40–7.36 (m, 2H), 7.31–7.25 (m, 2H), 7.04–6.98 (m, 1H), 6.32 (s, 1H), 3.55–3.45 (m, 2H), 1.89–1.81 (m, 6H), 1.80–1.75 (m, 6H), 1.69 (d, J = 13.0 Hz, 2H), 1.42–1.31 (m, 4H), 1.22–1.11 (m, 2H); 13C NMR (101 MHz, Chloroform-d) δ 154.9, 139.4, 128.8, 122.5, 119.7, 55.5, 31.9, 26.4, 25.6;
N-phenyl-3,4-dihydroisoquinoline-2(1H)-carboxamide (5t):
White solid (45.1 mg, 89%). 1H NMR (400 MHz, Chloroform-d) δ 7.46–7.42 (m, 2H), 7.32–7.27 (m, 2H), 7.25–7.17 (m, 3H), 7.15–7.10 (m, 1H), 7.05 (t, J = 7.4 Hz, 1H), 6.75 (s, 1H), 4.67 (s, 2H), 3.72 (t, J = 5.9 Hz, 2H), 2.91 (t, J = 5.9 Hz, 2H); 13C NMR (101 MHz, Chloroform-d) δ 155.2, 139.2, 135.0, 133.3, 128.9, 128.4, 126.8, 126.5, 126.4, 123.1, 120.3, 45.8, 41.6, 29.0;
1-benzyl-1-ethyl-3-phenylurea (5u):
Colorless liquid (42.8 mg, 84%). 1H NMR (400 MHz, Chloroform-d) δ 7.42–7.38 (m, 2H), 7.37–7.30 (m, 5H), 7.29–7.24 (m, 2H), 7.06–7.00 (m, 1H), 6.40 (s, 1H), 4.59 (s, 2H), 3.52–3.45 (m, 2H), 1.24 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, Chloroform-d) δ 155.4, 139.2, 137.7, 129.0, 128.8, 127.7, 127.1, 122.9, 119.9, 50.3, 42.5, 13.5. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C16H19N2O, 255.1492; found, 255.1500;
1-benzyl-1-isopropyl-3-phenylurea (5v):
White solid (48.8 mg, 91%), mp 108.8–109.9 °C. 1H NMR (400 MHz, Chloroform-d) δ 7.45–7.37 (m, 4H), 7.37–7.32 (m, 1H), 7.25–7.19 (m, 4H), 7.02–6.96 (m, 1H), 6.36 (s, 1H), 4.86–4.73 (m, 1H), 4.47 (s, 2H), 1.24 (d, J = 6.8 Hz, 6H); 13C NMR (101 MHz, Chloroform-d) δ 155.8, 139.3, 138.2, 129.2, 128.7, 127.8, 126.4, 122.8, 119.8, 46.4, 45.5, 20.8. HRMS (ESI-TOF) m/z: [M + H]+ calcd for C17H21N2O, 269.1648; found, 269.1657;
1,3-diphenylurea (5w):
White solid (22.5 mg, 52%). 1H NMR (400 MHz, DMSO-d6) δ 8.7 (s, 2H), 7.5 (dd, J = 8.6, 1.2 Hz, 4H), 7.3–7.2 (m, 4H), 7.0–6.9 (m, 2H); 13C NMR (101 MHz, DMSO-d6) δ 153.0, 140.2, 129.2, 122.3, 118.6.

4. Conclusions

In conclusion, we have disclosed a visible-light-promoted external catalyst-free procedure for the decarboxylation of dioxazolones to synthesize various phosphinimidic amides and ureas. The method has the advantages of no additional transition metals, economic raw materials, mild reaction conditions, and easy operation. It could be reasoned that the ppm Fe in the reaction mixture played a significant role in this transformation.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules27123648/s1. References [29,32,34,59,60,61,62,63] are cited in the Supplementary Materials. Synthetic procedure of starting materials, procedure and spectral data of products, copies of 1H-NMR, 13C-NMR, 31P-NMR, 19F-NMR spectra.

Author Contributions

Conceptualization, J.P., H.L. and K.S.; data curation, J.P., H.L. and B.Y.; methodology, J.P. and H.L.; supervision, K.S. and B.Y.; validation, B.Y.; writing—original draft, J.P.; writing—review and editing, K.S. and S.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Hunan Provincial Natural Science Foundation of China (2021JJ40432), and the National Natural Science Foundation of China (21971224, 22171249).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Not available.

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Molecules 27 03648 sch001 550
Scheme 1. The construction of N=P and N–C bonds from dioxazolones.
Scheme 1. The construction of N=P and N–C bonds from dioxazolones.
Molecules 27 03648 sch001
Molecules 27 03648 sch002 550
Scheme 2. Substrate scope for the synthesis of phosphinimidic amides.
Scheme 2. Substrate scope for the synthesis of phosphinimidic amides.
Molecules 27 03648 sch002
Molecules 27 03648 sch003 550
Scheme 3. Substrate scope for the synthesis of ureas. Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol) in solvent (2 mL) at room temperature for 5 h under the irradiation of 10 W 430 nm blue LED. Isolated yields were given; b 20 h.
Scheme 3. Substrate scope for the synthesis of ureas. Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol) in solvent (2 mL) at room temperature for 5 h under the irradiation of 10 W 430 nm blue LED. Isolated yields were given; b 20 h.
Molecules 27 03648 sch003
Molecules 27 03648 sch004 550
Scheme 4. (a) Preparation of amide compounds; (b) gram-scale synthesis of 3a.
Scheme 4. (a) Preparation of amide compounds; (b) gram-scale synthesis of 3a.
Molecules 27 03648 sch004
Molecules 27 03648 sch005 550
Scheme 5. Control experiments.
Scheme 5. Control experiments.
Molecules 27 03648 sch005
Molecules 27 03648 sch006 550
Scheme 6. Proposed reaction mechanism.
Scheme 6. Proposed reaction mechanism.
Molecules 27 03648 sch006
Table
Table 1. Optimization of reaction conditions a.
Table 1. Optimization of reaction conditions a.
Molecules 27 03648 i001
EntrySolventWavelengthYield (%)
1DCE430 nm11
21,4-dioxane430 nm23
3CH3OH430 nm14
4Acetone430 nm23
5DMF430 nm22
6CH3CN430 nm26
7THF430 nm0
8CH2Cl2430 nm81
9CH2Cl2460 nm22
10CH2Cl2390 nm63
11 bCH2Cl2Green LED0
12 cCH2Cl2White LED0
13 dCH2Cl2430 nm61
14 eCH2Cl2430 nm67
15 fCH2Cl2--0
16 gCH2Cl2430 nm<5
a Reaction conditions: 1a (0.1 mmol), 2a (0.1 mmol) in solvent (1 mL) at room temperature for 24 h under the irradiation of 10 W 430 nm blue LED. Yield is determined by 31P NMR; b Green LED (10 W); c White LED (10 W); d 1a (0.2 mmol); e 2a (0.2 mmol); f Without light; g Reaction in air.
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Pan, J.; Li, H.; Sun, K.; Tang, S.; Yu, B. Visible-Light-Induced Decarboxylation of Dioxazolones to Phosphinimidic Amides and Ureas. Molecules 2022, 27, 3648. https://doi.org/10.3390/molecules27123648

AMA Style

Pan J, Li H, Sun K, Tang S, Yu B. Visible-Light-Induced Decarboxylation of Dioxazolones to Phosphinimidic Amides and Ureas. Molecules. 2022; 27(12):3648. https://doi.org/10.3390/molecules27123648

Chicago/Turabian Style

Pan, Jie, Haocong Li, Kai Sun, Shi Tang, and Bing Yu. 2022. "Visible-Light-Induced Decarboxylation of Dioxazolones to Phosphinimidic Amides and Ureas" Molecules 27, no. 12: 3648. https://doi.org/10.3390/molecules27123648

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