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Article

An Unexpected Synthesis of 2-Sulfonylquinolines via Deoxygenative C2-Sulfonylation of Quinoline N-Oxides with Sulfonyl Chlorides

by
Wei Yang
†,
Zhong-Ying Tian
†,
Ying-Jun Lin
† and
Long-Yong Xie
*
College of Chemistry and Bioengineering, Hunan University of Science and Engineering, Yongzhou 425100, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally in this work.
Molecules 2024, 29(12), 2863; https://doi.org/10.3390/molecules29122863
Submission received: 28 May 2024 / Revised: 9 June 2024 / Accepted: 14 June 2024 / Published: 16 June 2024
(This article belongs to the Special Issue Recent Developments in Cross-Coupling Reactions)
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Abstract

:
A mild, efficient and practical protocol for the preparation of 2-sulfonylquinolines through CS2/Et2NH-induced deoxygenative C2-H sulfonylation of quinoline N-oxides with readily available RSO2Cl was developed. The reaction proceeded well under transition-metal-free conditions and exhibited a wide substrate scope and functional group tolerance. The preliminary studies suggested that the nucleophilic sulfonyl sources were generated in situ via the reaction of CS2, Et2NH and sulfonyl chlorides.

1. Introduction

Quinolines are an important class of heterocyclic compounds that are widely present in natural products, medicine, functional materials and other fields [1,2,3,4,5,6]. Among them, 2-sulfonylquinolines exhibit diverse biological activities and serve as important building blocks for complex molecules [7,8,9]. Consequently, great efforts have been devoted to the synthesis of such compounds. In general, there are two main methods for 2-sulfonylquinolines: (1) the cross-coupling reactions of 2-haloquinolines with sulfonylating agents [10,11,12,13,14,15,16], which suffer from the pre-halogenation of the quinoline substrates; (2) the direct deoxygenative C2-H sulfonylation of quinoline N-oxides with various sulfonylating agents [17,18,19,20,21,22,23,24,25,26,27,28]. Most 2-haloquinolines are not commercially available and are often obtained via the deoxygenative halogenation of quinoline N-oxides with some toxic and irritant halogenating reagents (POX3, SOCl2, CX4, CCl3CN, etc.) [29,30,31]. Therefore, the later represents a much more efficient and practical method. In the past few years, great achievements have been gained in the C-H functionalization of quinoline N-oxides including alkylation [32], alkenylation [33,34,35], alkoxylation [36,37,38,39], amination [40,41,42,43], sulfenylation [44], cyanation [45,46], amidation [47,48], arylation [49,50], etc. [51,52,53,54]. Particularly, the deoxygenative C2-sulfonylation of quinoline N-oxides has been regarded as one of the most important methods for 2-sulfonylquinolines. Various sulfonylating reagents including RSO2Na [17,19,20,22,28], RSO2NHNH2 [23], RSO2Cl [26,27] and RSO2H [18,25] were utilized for the construction of sulfonylated quinolines. Among them, most RSO2Na, RSO2NHNH2 and RSO2H cannot be obtained from commercial sources and need to be prepared from cheap and readily available RSO2Cl as starting materials under alkaline conditions. Therefore, from the point of view of synthetic efficiency, directly using sulfonyl chlorides as sulfonylating reagents for 2-sulfonylquinolines represents a much more attractive strategy. In this context, several reports on the deoxygenative C2-sulfonylation of quinoline N-oxides with sulfonyl chlorides towards 2-sulfonylquinolines have been presented. For instance, in 2015, Zhao and co-workers first developed an H-phosphonate-promoted deoxygenative C2-sulfonylation of quinoline N-oxides with sulfonyl chlorides under strong base conditions (Scheme 1a) [27]. In 2017, our group reported an ultrasound-assisted and zinc-dust-mediated one-pot synthesis of various 2-sulfonylquinolines with quinoline N-oxides and sulfonyl chlorides as starting materials (Scheme 1b) [26]. Despite these advances, these reactions require the use of moisture-sensitive H-phosphonate and large amounts of a strong base or the stoichiometric transition metals, which may result in metal residues of the finished products. Therefore, the development of many more mild and efficient methods for the synthesis of 2-sulfonylquinolines under transition-metal-free conditions is still in high demand.
With our continuing interest in the deoxygenative C2-H functionalization of quinoline N-oxides [25,55,56,57,58], herein, we report on an unexpected method for 2-sulfonylquinolines via CS2/Et2NH-promoted deoxygenative C2-sulfonylation of quinoline N-oxides with commercially available sulfonyl chlorides (Scheme 1c). In this reaction, sulfonyl chlorides act as both sulfonyl sources and electrophilic reagents utilized for activating quinoline N-oxides.

2. Results and Discussion

In our initial study, we speculated that diethylcarbamodithioic acid (Et2NCS2H) generated in situ through the reaction of CS2 and Et2NH could serve as a sulfur-containing nucleophilic reagent, which might further attack quinoline N-oxide at the C2 position in the presence of TsCl as an electrophilic activating reagent. With this in mind, a reaction of quinoline N-oxide (1a) and TsCl (2a) was carried out with 1.2 equivalents of carbon disulfide and 1.5 equivalents of diethylamine at room temperature for approximately 0.5 h using THF as the reaction solvent. Beyond our expectation, quinolin-2-yl diethylcarbamodithioate 3aa’ was not detected in the reaction mixture, but 2-tosylquinoline 3aa was isolated in 55% yield (Table 1, entry 1). To further optimize the reaction conditions of this unexpected sulfonylation reaction, the influence of different solvents on the reaction was explored, among which dichloromethane was identified as the most effective solvent, producing product 3aa in 67% yield (entry 2), while other investigated solvents resulted in lower yields (entries 3–7). Among the amines tested, dimethylamine produced 3aa in 43% yield (entry 8), while diisopropylamine (entry 9), morpholine (entry 10) and piperidine (entry 11) produced 3aa in only around 10% yields. Particularly, triethylamine was found to be unsuitable for the present transformation (entry 12). Increasing the amount of 2a did not significantly impact the yield of 3aa (entries 13 and 14). However, a decrease to 1.5 equivalents resulted in a 53% yield of 3aa (entry 15). Moreover, increasing the amount of diethylamine to 2 equivalents improved the yield of 3aa to 79% (entry 16), and further optimization by increasing the amount of carbon disulfide to 1.5 equivalents increased the yield to 84% (entry 17). Control experiments confirmed that the presence of carbon disulfide and secondary amine is essential for the formation of the sulfonylation products (entries 19 and 20).
After obtaining the optimal reaction conditions (Table 1, entry 17), we proceeded to investigate the substrate scope and limitations with respect to various heterocyclic N-oxides, as illustrated in Scheme 2. We found that a range of quinoline N-oxides were suitable for the current transformation and produced the corresponding products in 62%–84% yields (3aa–3pa). It is worth noting that some important functional groups, such as alkyl (3ba, 3da, 3fa, 3ka and 3oa), methoxy (3ga), F (3ha), Cl (3ca, 3ea, 3ia and 3la), Br (3ja and 3ma), and aryl (3pa) groups, at different positions on the quinoline rings were compatible with the reaction. In addition, tri-substituted quinoline N-oxide 1q also reacted well with TsCl and provided the expected product 3qa in 62% yield. However, isoquinoline N-oxide (3ra), quinoxaline N-oxide (3sa), pyrazine N-oxide (3ta) and several substituted pyridine N-oxides (3ua–3wa) did not yield the desired products, which was likely due to their lower activities in contrast to quinoline N-oxides, which can be speculated from the below-mentioned possible mechanism that nucleophilic addition to a pyridine N-oxide would result in complete loss of aromaticity whereas with quinoline N-oxide, there would only be a partial loss of aromaticity. Interestingly, 4-phenylpyridine N-oxide as a potential substrate also produced the expected product 3xa in 51% yield.
We then turned our attention to investigate the scope of sulfonyl chlorides, as shown in Scheme 3. We found that various aryl sulfonyl chlorides bearing electron-donating, electron-withdrawing or steric hindered functional groups at the different positions of the phenyl rings all reacted well with 1a to produce the corresponding products 3ab–3an in 63–84% yields. The reaction was compatible with a range of valuable substitutions, such as alkyl (3ai and 3am), methoxy (3ac), halogen atoms (3ad–3af, 3aj and 3an), acetyl (3ag) and trifluoromethoxy (3ah). In addition, di-substituted aryl sulfonyl chlorides were found efficient for the reaction and produced the desired products 3ak and 3al in 79 and 74% yields, respectively. To our delight, thiophene-2-sulfonyl chloride was also a suitable substrate to produce the target product 3ao in 62% yield. However, aliphatic sulfonyl chlorides including methanesulfonyl chloride and trifluoromethanesulfonyl chloride failed to produce the corresponding products (3ap and 3aq), presumably owing to their relatively poor abilities for activating quinoline N-oxides compared with aryl sulfonyl chlorides.
To demonstrate the synthetic application of this method, a gram-scale experiment between quinoline N-oxide 1a (5 mmol, 0.7253 g) and TsCl 2a was carried out under standard conditions. As anticipated, the expected product 3aa was isolated in 81% yield (Scheme 4).
To investigate the underlying reaction mechanism, a series of control experiments were conducted, as illustrated in Scheme 5. Initially, the reaction of quinoline 1a’ and 2a under standard conditions failed to produce 3aa, highlighting the necessity of nitrogen–oxygen groups for the reaction (Scheme 5a). Subsequently, the model reaction was carried out under standard conditions with the addition of TEMPO or BHT as the free radical inhibitors (Scheme 5b). The results indicated that the yields of product 3aa did not exhibit significant decreases, suggesting that the reaction may not proceed through a free radical pathway. Furthermore, the intermediate IM-1 was synthesized by reacting CS2 with diethylamine, followed by the addition of quinoline N-oxide 1a and p-toluenesulfonyl chloride 2a, resulting in a yield of 84% for 3aa. Meanwhile, compound 4a was also isolated and characterized by NMR (Scheme 5c,d). To investigate whether the formation of 4a necessitates the involvement of quinoline N-oxide, a three-component reaction involving CS2, diethylamine, and p-toluenesulfonyl chloride 2a was conducted, giving 4a in 83% yield at room temperature in DCM. It is hypothesized that key intermediate 5a may also be generated during the reaction (Scheme 5e). Next, compound 5a was synthesized using p-toluenesulfinic acid and diethylamine, and upon its reaction with quinoline N-oxide in the presence of p-toluenesulfonyl chloride, product 3aa was obtained in 85% yield (Scheme 5f,g), indicating that the in situ generated 5a could serve as the sulfonyl source in the current reaction. Finally, the model reaction was carried out in the absence of CS2 and Et2NH (Scheme 5h), and the results showed that 3aa was not observed, which further demonstrated the necessity of CS2-Et2NH in the present reaction.
Based on the above-mentioned control experiments and relevant reports in the literature [44,59], a possible reaction pathway was speculated, as shown in Scheme 6. First, a reaction between CS2 and Et2NH occurred and gave an intermediate IM-1, which further reacted with 2a to give IM-2. In the presence of IM-1, intermediate IM-2 was transformed to 4a with the release of a sulfonyl anion (Ts−). Meanwhile, quinoline N-oxide 1a was activated by compound 2a to produce intermediate IM-3. Then, the resulting sulfonyl anion (Ts−) attacked IM-3 at the C2 position, providing intermediate IM-4, which underwent an elimination process to afford the desired 3aa.

3. Experimental Section

3.1. General Information

Unless otherwise noted, all solvents and reagents in this study were commercial and used without further purification. 1H, 13C and 19F NMR spectra were recorded at 400, 100 and 376 MHz, respectively (see Supplementary Materials). Chemical shifts were quoted in ppm relative to CDCl3 (δH = 7.26, δC = 77.0 ppm). The data are reported as follows: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, dd = doublet of doublet, etc. The reactions were monitored by thin-layer chromatography (TLC) using GF254 silica gel-coated TLC plates. Mass spectra were performed on a spectrometer operating on ESI-TOF. Melting points were measured on a melting point apparatus and were uncorrected.

3.2. General Procedure for the Preparation of 2-Sulfonylquinolines 3

To a round-bottom flask were consecutively added quinoline N-oxide 1 (0.3 mmol), CS2 (0.45 mmol), diethylamine (0.6 mmol) and sulfonyl chloride 2 (0.6 mmol) in CH2Cl2 (3 mL). The reaction mixture was stirred at room temperature for about 15–30 min, which was monitored by TLC. Upon completion, CH2Cl2 (10 mL) and water (10 mL) were added to the mixture, the organic layer was separated and the aqueous layer was further extracted with CH2Cl2 (2 × 10 mL). The organic phases were combined and dried with anhydrous Na2SO4, followed by filtration and concentration under vacuo. The residue was purified by a flash chromatography column over silica gel to produce the desired product 3.

3.3. Gram-Scale Synthesis of 3aa

To a round-bottom flask were consecutively added quinoline N-oxides 1 (5 mmol, 0.7253 g), CS2 (7.5 mmol, 0.5696 g), diethylamine (10 mmol, 0.7309 g) and TsCl (10 mmol, 1.8999 g) in CH2Cl2 (50 mL). The reaction mixture was stirred at room temperature for about 0.5 h. Upon completion, water (30 mL) was added to quench the reaction. The organic layer was separated, and the aqueous layer was further extracted with CH2Cl2 (2 × 20 mL). The organic phases were combined and dried with anhydrous Na2SO4, followed by filtration and concentration under vacuo. The residue was purified by a flash chromatography column over silica gel to produce 1.1464 g of 3aa, yield: 81%.

3.4. Characterization Data of Products 3aa–3ta, 3xa and 3ab–3ap

2-tosylquinoline (3aa): White solid (71.3 mg, 84%), m.p.: 141–142 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.36 (d, J = 8.5 Hz, 1H), 8.18 (t, J = 8.6 Hz, 2H), 8.02 (d, J = 8.1 Hz, 2H), 7.86 (d, J = 8.2 Hz, 1H), 7.77 (t, J = 7.6 Hz, 1H), 7.64 (t, J = 7.5 Hz, 1H), 7.32 (d, J = 8.0 Hz, 2H), 2.39 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 158.3, 147.4, 144.8, 138.6, 136.1, 130.9, 130.4, 129.7, 129.1, 129.0, 128.8, 127.6, 117.6, 21.6. NMR data matched previously reported values [20].
3-methyl-2-tosylquinoline (3ba): White solid (64.2 mg, 72%), m.p.: 114–115 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.05 (s, 1H), 7.93 (t, J = 7.7 Hz, 3H), 7.76 (d, J = 8.1 Hz, 1H), 7.65 (t, J = 7.5 Hz, 1H), 7.58 (t, J = 7.4 Hz, 1H), 7.36 (d, J = 7.9 Hz, 2H), 2.86 (s, 3H), 2.46 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 157.0, 144.7, 144.5, 139.8, 135.8, 129.9, 129.7, 129.4, 129.3, 129.1, 128.9, 128.5, 126.6, 21.7, 18.8. NMR data matched previously reported values [22].
3-chloro-2-tosylquinoline (3ca): White solid (67.5 mg, 71%), m.p.: 108–109 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.28 (s, 1H), 8.06 (d, J = 8.5 Hz, 1H), 7.96 (d, J = 7.8 Hz, 2H), 7.76 (q, J = 8.3 Hz, 2H), 7.71–7.64 (m, 1H), 7.36 (d, J = 7.9 Hz, 2H), 2.46 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 153.6, 145.0, 144.3, 139.0, 135.2, 130.9, 130.3, 130.1, 129.6, 129.5, 129.4, 126.5, 124.7, 21.7; HRMS (ESI): m/z [M + H]+ calcd. for C16H13ClNO2S: 318.0350; found: 318.0353.
4-methyl-2-tosylquinoline (3da): White solid (58.8 mg, 66%), m.p.: 144–145 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.15 (d, J = 8.4 Hz, 1H), 8.04–7.96 (m, 4H), 7.74 (t, J = 7.6 Hz, 1H), 7.64 (t, J = 7.4 Hz, 1H), 7.31 (d, J = 7.3 Hz, 2H), 2.77 (s, 3H), 2.38 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 157.9, 147.8, 147.2, 144.6, 136.3, 131.0, 130.4, 129.7, 129.0, 128.8, 128.7, 123.7, 118.0, 21.6, 19.1. NMR data matched previously reported values [26].
4-chloro-2-tosylquinoline (3ea): White solid (65.6 mg, 69%), m.p.: 168–169 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.26 (s, 1H), 8.22 (d, J = 8.4 Hz, 1H), 8.17 (d, J = 8.5 Hz, 1H), 8.01 (d, J = 8.1 Hz, 2H), 7.81 (t, J = 7.2 Hz, 1H), 7.73 (t, J = 7.6 Hz, 1H), 7.33 (d, J = 7.9 Hz, 2H), 2.39 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 158.1, 148.0, 145.1, 135.5, 131.7, 130.7, 130.1, 129.8, 129.1, 126.9, 124.1, 117.8, 21.6. NMR data matched previously reported values [13].
6-isopropyl-2-tosylquinoline (3fa): White solid (71.2 mg, 73%), m.p.: 147–148 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.28 (d, J = 8.4 Hz, 1H), 8.15 (d, J = 8.6 Hz, 1H), 8.10 (d, J = 8.7 Hz, 1H), 8.00 (d, J = 7.9 Hz, 2H), 7.71–7.60 (m, 2H), 7.30 (d, J = 7.7 Hz, 2H), 3.15–3.04 (m, 1H), 2.38 (s, 3H), 1.32 (d, J = 6.8 Hz, 6H); 13C NMR (100 MHz, Chloroform-d) δ 157.4, 150.2, 146.4, 144.6, 138.1, 136.4, 131.0, 130.2, 129.7, 128.9, 128.9, 123.6, 117.7, 34.2, 23.6, 21.6. NMR data matched previously reported values [26].
6-methoxy-2-tosylquinoline (3ga): White solid (71.4 mg, 76%), m.p.: 162–163 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.20 (d, J = 8.6 Hz, 1H), 8.12 (d, J = 8.6 Hz, 1H), 8.03 (d, J = 9.3 Hz, 1H), 7.99 (d, J = 8.0 Hz, 2H), 7.39 (dd, J = 9.3, 2.6 Hz, 1H), 7.30 (d, J = 8.0 Hz, 2H), 7.07 (d, J = 2.4 Hz, 1H), 3.92 (s, 3H), 2.38 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 159.7, 155.6, 144.5, 143.6, 136.8, 136.5, 131.7, 130.3, 129.7, 128.8, 124.2, 118.1, 104.6, 55.7, 21.6. NMR data matched previously reported values [19].
6-fluoro-2-tosylquinoline (3ha): White solid (69.5 mg, 77%), m.p.: 123–124 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.32 (d, J = 8.6 Hz, 1H), 8.21 (d, J = 8.7 Hz, 1H), 8.20–8.13 (m, 1H), 8.01 (d, J = 8.0 Hz, 2H), 7.55 (t, J = 8.7 Hz, 1H), 7.48 (d, J = 8.5 Hz, 1H), 7.33 (d, J = 8.0 Hz, 2H), 2.41 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 161.9 (d, JC-F = 251.6 Hz), 157.9, 144.9, 144.5, 137.9 (d, JC-F = 5.7 Hz), 135.9, 133.1 (d, JC-F = 9.5 Hz), 129.8, 129.7, 129.0, 121.5 (d, JC-F = 26.0 Hz), 118.5, 110.7 (d, JC-F = 21.9 Hz), 21.6; 19F NMR (376 MHz, Chloroform-d) δ −108.35. NMR data matched previously reported values [19].
6-chloro-2-tosylquinoline (3ia): White solid (75.1 mg, 79%), m.p.: 165–166 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.28 (d, J = 8.6 Hz, 1H), 8.21 (d, J = 8.4 Hz, 1H), 8.10 (d, J = 8.9 Hz, 1H), 8.00 (d, J = 7.9 Hz, 2H), 7.88–7.83 (m, 1H), 7.70 (d, J = 9.1 Hz, 1H), 7.33 (d, J = 7.8 Hz, 2H), 2.40 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 158.7, 145.8, 145.0, 137.7, 135.8, 135.2, 132.0, 131.9, 129.8, 129.3, 129.1, 126.3, 118.6, 21.6. NMR data matched previously reported values [18].
6-bromo-2-tosylquinoline (3ja): White solid (83.4 mg, 77%), m.p.: 179–180 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.27 (d, J = 8.5 Hz, 1H), 8.20 (d, J = 8.6 Hz, 1H), 8.05–7.98 (m, 4H), 7.83 (dd, J = 9.0, 2.2 Hz, 1H), 7.33 (d, J = 8.0 Hz, 2H), 2.40(s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 158.7, 145.9, 145.0, 137.6, 135.7, 134.5, 131.9, 129.8, 129.7, 129.1, 123.5, 118.6, 21.7. NMR data matched previously reported values [18].
7-methyl-2-tosylquinoline (3ka): White solid (58.8 mg, 66%), m.p.: 209–210 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.30 (d, J = 8.5 Hz, 1H), 8.12 (d, J = 8.5 Hz, 1H), 8.01 (d, J = 8.0 Hz, 2H), 7.94 (s, 1H), 7.75 (d, J = 8.4 Hz, 1H), 7.47 (d, J = 8.4 Hz, 1H), 7.32 (d, J = 8.0 Hz, 2H), 2.54 (s, 3H), 2.39 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 158.2, 147.7, 144.6, 141.6, 138.2, 136.2, 131.4, 129.7, 129.2, 129.0, 127.2, 126.9, 116.8, 21.8, 21.6. NMR data matched previously reported values [23].
7-chloro-2-tosylquinoline (3la): White solid (60.9 mg, 64%), m.p.: 173–174 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.35 (d, J = 8.5 Hz, 1H), 8.20 (d, J = 8.6 Hz, 1H), 8.16 (s, 1H), 8.00 (d, J = 8.0 Hz, 2H), 7.81 (d, J = 8.8 Hz, 1H), 7.60 (d, J = 8.7 Hz, 1H), 7.34 (d, J = 7.9 Hz, 2H), 2.41 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 159.5, 147.7, 145.0, 138.6, 137.1, 135.7, 130.2, 129.8, 129.2, 128.8, 128.0, 127.1, 117.7, 21.7. NMR data matched previously reported values [60].
7-bromo-2-tosylquinoline (3ma): White solid (72.6 mg, 67%), m.p.: 186–187 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.39–8.32 (m, 2H), 8.22 (d, J = 8.6 Hz, 1H), 8.00 (d, J = 7.9 Hz, 2H), 7.74 (s, 2H), 7.34 (d, J = 7.9 Hz, 2H), 2.42 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 159.4, 147.8, 145.0, 138.7, 135.6, 132.7, 132.6, 129.8, 129.2, 128.8, 127.3, 125.3, 117.9, 21.7; HRMS (ESI): m/z [M + H]+ calcd. for C16H13BrNO2S: 361.9845; found: 361.9849.
2-tosyl-7-(trifluoromethyl)quinoline (3na): White solid (76.9 mg, 73%), m.p.: 162–163 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.45 (d, J = 9.1 Hz, 2H), 8.32 (d, J = 8.5 Hz, 1H), 8.04–7.99 (m, 3H), 7.82 (d, J = 8.4 Hz, 1H), 7.35 (d, J = 8.0 Hz, 2H), 2.42 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 160.0, 146.3, 145.2, 138.8, 135.4, 132.7 (q, JC-F = 33.0 Hz), 130.0, 129.9, 129.2, 129.0, 128.2 (q, JC-F = 4.3 Hz), 124.6 (q, JC-F = 2.8 Hz), 123.4 (q, JC-F = 271.1 Hz), 119.4, 21.7. NMR data matched previously reported values [60].
8-methyl-2-tosylquinoline (3oa): White solid (65.9 mg, 74%), m.p.: 125–126 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.32 (d, J = 8.5 Hz, 1H), 8.19 (d, J = 8.5 Hz, 1H), 8.06 (d, J = 7.9 Hz, 2H), 7.68 (d, J = 8.1 Hz, 1H), 7.59 (d, J = 6.8 Hz, 1H), 7.51 (t, J = 7.5 Hz, 1H), 7.34 (d, J = 7.9 Hz, 2H), 2.68 (s, 3H), 2.41 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 157.3, 146.4, 144.6, 138.7, 138.4, 135.9, 130.8, 129.5, 129.3, 128.9, 128.8, 125.5, 116.7, 21.6, 17.5. NMR data matched previously reported values [22].
8-(4-bromophenyl)-2-tosylquinoline (3pa): White solid (85.2 mg, 65%), m.p.: 137–138 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.43 (dd, J = 8.5, 2.9 Hz, 1H), 8.25 (dd, J = 8.5, 2.9 Hz, 1H), 7.90–7.79 (m, 3H), 7.79–7.72 (m, 1H), 7.75–7.64 (m, 1H), 7.47 (dd, J = 8.1, 2.8 Hz, 2H), 7.31–7.20 (m, 4H), 2.46 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 158.6, 144.8, 144.3, 140.0, 139.0, 136.8, 134.9, 132.2, 131.1, 130.8, 129.7, 129.4, 129.2, 128.8, 127.6, 121.7, 116.6, 21.7; HRMS (ESI): m/z [M + H]+ calcd. for C22H17BrNO2S: 438.0158; found: 438.0155.
4-chloro-6,7-dimethoxy-2-tosylquinoline (3qa): White solid (70.1 mg, 62%), m.p.: 196–197 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.13 (s, 1H), 7.99 (d, J = 8.1 Hz, 2H), 7.48 (s, 1H), 7.38 (s, 1H), 7.33 (d, J = 8.0 Hz, 2H), 4.06 (s, 3H), 4.02 (s, 3H), 2.40 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 155.6, 154.2, 152.8, 145.6, 144.8, 142.0, 136.3, 129.8, 128.9, 123.4, 116.7, 108.9, 101.3, 56.5, 56.4, 21.7; HRMS (ESI): m/z [M + H]+ calcd. for C18H17ClNO4S: 378.0561; found: 378.0566.
4-phenyl-2-tosylpyridine (3xa): White solid (47.3 mg, 51%), m.p.: 149–150 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.68 (s, 1H), 8.41 (s, 1H), 7.98 (d, J = 7.0 Hz, 2H), 7.65 (d, J = 14.2 Hz, 3H), 7.55–7.41 (m, 3H), 7.34 (d, J = 7.1 Hz, 2H), 2.41 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 159.7, 150.8, 144.8, 136.5, 135.9, 130.0, 129.8, 129.4, 129.0, 127.1, 124.3, 119.8, 21.6. NMR data matched previously reported values [22].
2-(phenylsulfonyl)quinoline (3ab): White solid (57.3 mg, 71%), m.p.: 159–160 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.37 (d, J = 8.5 Hz, 1H), 8.21 (d, J = 8.5 Hz, 1H), 8.19–8.12 (m, 3H), 7.87 (d, J = 8.1 Hz, 1H), 7.78 (t, J = 7.5 Hz, 1H), 7.66 (d, J = 7.7 Hz, 1H), 7.59 (d, J = 7.2 Hz, 1H), 7.53 (t, J = 7.5 Hz, 2H); 13C NMR (100 MHz, Chloroform-d) δ 158.0, 147.4, 139.0, 138.7, 133.7, 131.0, 130.3, 129.2, 129.0, 128.9, 128.8, 127.7, 117.7. NMR data matched previously reported values [16].
2-((4-methoxyphenyl)sulfonyl)quinoline (3ac): White solid (65.5 mg, 73%), m.p.: 131–132 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.36 (d, J = 8.5 Hz, 1H), 8.21–8.13 (m, 2H), 8.07 (d, J = 8.7 Hz, 2H), 7.86 (d, J = 8.0 Hz, 1H), 7.78 (t, J = 7.7 Hz, 1H), 7.65 (t, J = 7.5 Hz, 1H), 6.99 (d, J = 8.7 Hz, 2H), 3.84 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 163.9, 158.6, 147.4, 138.6, 133.8, 131.3, 130.9, 130.5, 129.0, 128.7, 127.6, 117.5, 114.4, 55.6. NMR data matched previously reported values [19].
2-((4-fluorophenyl)sulfonyl)quinoline (3ad): White solid (71.5 mg, 83%), m.p.: 124–125 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.39 (d, J = 8.5 Hz, 1H), 8.24–8.11 (m, 4H), 7.88 (d, J = 8.2 Hz, 1H), 7.79 (t, J = 7.6 Hz, 1H), 7.66 (t, J = 7.5 Hz, 1H), 7.21 (t, J = 8.5 Hz, 2H); 13C NMR (100 MHz, Chloroform-d) δ 165.9 (d, JC-F = 254.9 Hz), 157.9, 147.4, 138.8, 134.9 (d, JC-F = 3.1 Hz), 132.0 (d, JC-F = 9.6 Hz), 131.1, 130.3, 129.3, 128.8, 127.7, 117.4, 116.4 (d, JC-F = 22.5 Hz); 19F NMR (376 MHz, Chloroform-d) δ −103.39. NMR data matched previously reported values [18].
2-((4-chlorophenyl)sulfonyl)quinoline (3ae): White solid (74.5 mg, 82%), m.p.: 190–191 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.40 (dd, J = 8.4, 2.3 Hz, 1H), 8.20 (dd, J = 8.4, 2.4 Hz, 1H), 8.15 (d, J = 8.1 Hz, 1H), 8.08 (dd, J = 8.2, 2.4 Hz, 2H), 7.89 (d, J = 7.2 Hz, 1H), 7.80 (t, J = 8.3 Hz, 1H), 7.68 (t, J = 7.0 Hz, 1H), 7.51 (dd, J = 8.2, 2.4 Hz, 2H); 13C NMR (100 MHz, Chloroform-d) δ 157.7, 147.4, 140.5, 138.8, 137.5, 131.1, 130.5, 130.3, 129.4, 129.3, 128.9, 127.7, 117.5. NMR data matched previously reported values [20].
2-((4-bromophenyl)sulfonyl)quinoline (3af): White solid (81.2 mg, 78%), m.p.: 146–147 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.39 (d, J = 8.5 Hz, 1H), 8.20 (d, J = 8.5 Hz, 1H), 8.15 (d, J = 8.5 Hz, 1H), 8.00 (d, J = 8.4 Hz, 2H), 7.88 (d, J = 8.2 Hz, 1H), 7.80 (t, J = 7.7 Hz, 1H), 7.70–7.64 (m, 3H); 13C NMR (100 MHz, Chloroform-d) δ 157.7, 147.4, 138.8, 138.0, 132.4, 131.1, 130.6, 130.3, 129.3, 129.2, 128.8, 127.7, 117.5. NMR data matched previously reported values [20].
1-(4-(quinolin-2-ylsulfonyl)phenyl)ethanone (3ag): White solid (78.4 mg, 84%), m.p.: 153–154 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.40 (d, J = 8.5 Hz, 1H), 8.26–8.20 (m, 3H), 8.13 (d, J = 8.6 Hz, 1H), 8.07 (d, J = 8.2 Hz, 2H), 7.88 (d, J = 8.2 Hz, 1H), 7.79 (t, J = 7.5 Hz, 1H), 7.67 (t, J = 7.5 Hz, 1H), 2.62 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 196.8, 157.4, 147.4, 145.0, 142.8, 140.7, 138.9, 131.2, 130.3, 129.4, 128.9, 128.7, 127.7, 117.6, 26.9. NMR data matched previously reported values [26].
2-((4-(trifluoromethoxy)phenyl)sulfonyl)quinoline (3ah): White solid (66.7 mg, 63%), m.p.: 162–163 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.40 (d, J = 8.5 Hz, 1H), 8.31–8.18 (m, 3H), 8.15 (d, J = 8.5 Hz, 1H), 7.89 (d, J = 8.2 Hz, 1H), 7.80 (t, J = 7.7 Hz, 1H), 7.67 (t, J = 7.5 Hz, 1H), 7.35 (d, J = 8.4 Hz, 2H); 13C NMR (100 MHz, Chloroform-d) δ 157.6, 153.0, 147.4, 138.9, 137.2, 131.4, 131.1, 130.3, 129.4, 128.9, 127.7, 122.8 (q, JC-F = 273.1 Hz), 120.7, 117.5; 19F NMR (376 MHz, Chloroform-d) δ -57.64. NMR data matched previously reported values [28].
2-(m-tolylsulfonyl)quinoline (3ai): White solid (68.8 mg, 81%), m.p.: 124–125 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.37 (d, J = 8.4 Hz, 1H), 8.19 (t, J = 7.7 Hz, 2H), 7.96–7.90 (m, 2H), 7.87 (d, J = 8.1 Hz, 1H), 7.78 (t, J = 7.7 Hz, 1H), 7.65 (t, J = 7.1 Hz, 1H), 7.43–7.35 (m, 2H), 2.41 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 158.1, 147.4, 139.3, 138.9, 138.7, 134.5, 130.9, 130.4, 129.2, 129.2, 128.9, 128.8, 127.7, 126.1, 117.8, 21.3. NMR data matched previously reported values [13].
2-((3-bromophenyl)sulfonyl)quinoline (3aj): White solid (79.1 mg, 76%), m.p.: 115–116 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.40 (d, J = 8.5 Hz, 1H), 8.27 (s, 1H), 8.20 (d, J = 8.5 Hz, 1H), 8.16 (d, J = 8.6 Hz, 1H), 8.08 (d, J = 7.9 Hz, 1H), 7.89 (d, J = 8.2 Hz, 1H), 7.80 (t, J = 7.7 Hz, 1H), 7.69 (dt, J = 15.3, 7.8 Hz, 2H), 7.41 (t, J = 7.9 Hz, 1H); 13C NMR (100 MHz, Chloroform-d) δ 157.4, 147.4, 140.9, 138.9, 136.7, 131.8, 131.1, 130.5, 130.3, 129.4, 128.9, 127.7, 127.6, 123.0, 117.6. NMR data matched previously reported values [18].
2-((3-chloro-4-fluorophenyl)sulfonyl)quinoline (3ak): White solid (76.1 mg, 79%), m.p.: 128–129 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.42 (d, J = 8.5 Hz, 1H), 8.21 (t, J = 7.7 Hz, 2H), 8.15 (d, J = 8.6 Hz, 1H), 8.09–8.03 (m, 1H), 7.90 (d, J = 8.2 Hz, 1H), 7.81 (t, J = 7.6 Hz, 1H), 7.69 (t, J = 7.5 Hz, 1H), 7.30 (t, J = 8.5 Hz, 1H); 13C NMR (100 MHz, Chloroform-d) δ 161.4 (d, JC-F = 257.0 Hz), 157.4, 147.4, 139.0, 136.0 (d, JC-F = 3.9 Hz), 132.0 (d, JC-F = 1.1 Hz), 131.2, 130.3, 129.8 (d, JC-F = 8.8 Hz), 129.5, 128.9, 127.7, 122.5 (d, JC-F = 18.6 Hz), 117.4 (d, JC-F = 22.3 Hz), 117.4; 19F NMR (376 MHz, Chloroform-d) δ −105.56. NMR data matched previously reported values [26].
2-((3,4-difluorophenyl)sulfonyl)quinoline (3al): White solid (67.7 mg, 74%), m.p.: 126–127 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.41 (d, J = 8.5 Hz, 1H), 8.20 (d, J = 8.5 Hz, 1H), 8.15 (d, J = 8.6 Hz, 1H), 8.00 (t, J = 8.2 Hz, 1H), 7.92 (dd, J = 14.8, 8.5 Hz, 2H), 7.81 (t, J = 7.7 Hz, 1H), 7.68 (t, J = 7.5 Hz, 1H), 7.33 (q, J = 8.7 Hz, 1H); 13C NMR (100 MHz, Chloroform-d) δ 157.4, 153.9 (dd, JC-F = 257.2 Hz, 12.5 Hz), 150.1 (dd, JC-F = 253.5 Hz, 12.5 Hz), 147.4, 139.0, 135.7 (dd, JC-F = 4.8 Hz, 3.7 Hz), 131.2, 130.3, 129.5, 128.9, 127.7, 126.4 (dd, JC-F = 7.8 Hz, 4.0 Hz), 119.1 (dd, JC-F = 19.8 Hz, 1.9 Hz), 118.2 (d, JC-F = 18.4 Hz), 117.4. NMR data matched previously reported values [26].
2-(o-tolylsulfonyl)quinoline (3am): White solid (61.1 mg, 72%), m.p.: 115–116 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.41 (d, J = 8.5 Hz, 1H), 8.33 (d, J = 7.8 Hz, 1H), 8.19 (d, J = 8.6 Hz, 1H), 8.13 (d, J = 8.6 Hz, 1H), 7.91 (d, J = 8.2 Hz, 1H), 7.78 (d, J = 8.2 Hz, 1H), 7.68 (t, J = 7.5 Hz, 1H), 7.52 (t, J = 7.4 Hz, 1H), 7.44 (t, J = 7.6 Hz, 1H), 7.28 (s, 1H), 2.58 (s, 3H); 13C NMR (100 MHz, Chloroform-d) δ 158.1, 147.1, 139.1, 138.6, 137.1, 133.9, 132.4, 130.9, 130.6, 130.3, 129.1, 128.8, 127.7, 126.3, 117.7, 20.7. NMR data matched previously reported values [20].
2-((2-chlorophenyl)sulfonyl)quinoline (3an): White solid (61.8 mg, 68%), m.p.: 166–167 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.54–8.46 (m, 1H), 8.43 (d, J = 8.5 Hz, 1H), 8.32 (d, J = 8.6 Hz, 1H), 8.04 (d, J = 8.5 Hz, 1H), 7.91 (d, J = 8.1 Hz, 1H), 7.75 (t, J = 7.5 Hz, 1H), 7.66 (t, J = 7.4 Hz, 1H), 7.60–7.52 (m, 2H), 7.46–7.37 (m, 1H); 13C NMR (100 MHz, Chloroform-d) δ 157.3, 147.1, 138.3, 136.7, 134.9, 133.0, 132.1, 131.5, 130.9, 130.2, 129.2, 129.0, 127.8, 127.1, 118.3. NMR data matched previously reported values [19].
2-(thiophen-2-ylsulfonyl)quinoline (3ao): White solid (51.2 mg, 62%), m.p.: 145–146 °C. 1H NMR (400 MHz, Chloroform-d) δ 8.39 (d, J = 8.5 Hz, 1H), 8.20 (d, J = 8.4 Hz, 2H), 7.92–7.86 (m, 2H), 7.83–7.77 (m, 1H), 7.75–7.70 (m, 1H), 7.69–7.63 (m, 1H), 7.15–7.08 (m, 1H); 13C NMR (100 MHz, Chloroform-d) δ 158.0, 147.4, 139.7, 138.9, 135.3, 135.3, 131.1, 130.4, 129.3, 128.9, 127.9, 127.7, 117.3. NMR data matched previously reported values [27].
Diethylcarbamodithioic acid (IM-1): Yellow oil, 1H NMR (400 MHz, Chloroform-d) δ 8.07 (s, 1H), 3.99 (s, 2H), 3.09 (q, J = 7.3 Hz, 2H), 1.39–1.26 (m, 3H), 1.16 (t, J = 7.0 Hz, 3H); 13C NMR (100 MHz, Chloroform-d) δ 208.1, 47.6, 40.8, 12.1, 10.6.
Tetraethylthiuram Disulfide (4a): White solid; 1H NMR (400 MHz, Chloroform-d) δ 4.17–3.76 (m, 8H), 1.55–1.37 (m, 6H), 1.34–1.20 (m, 6H); 13C NMR (100 MHz, Chloroform-d) δ 192.5, 51.9, 47.5, 13.3, 11.3.
Diethylamine 4-methylbenzenesulfinate (5a): Yellow oil; 1H NMR (400 MHz, Chloroform-d) δ 9.73 (s, 2H), 7.48 (d, J = 7.8 Hz, 2H), 7.14 (d, J = 7.7 Hz, 2H), 2.68 (q, J = 7.2 Hz, 4H), 2.29 (s, 3H), 1.18 (t, J = 7.3 Hz, 6H); 13C NMR (100 MHz, Chloroform-d) δ 153.3, 139.0, 128.8, 123.8, 41.4, 21.1, 10.9.

4. Conclusions

In summary, we have developed a practical and efficient approach to the synthesis of 2-sulfonylquinolines via deoxygenative C2-H sulfonylation of quinoline N-oxides with sulfonyl chlorides in the presence of CS2 and diethylamine. The reaction proceeds under mild and transition-metal-free conditions, providing the sulfonylation products bearing various functional groups in satisfactory yields. In this reaction, sulfonyl chlorides act as both electrophilic reagents for activating quinoline N-oxides and readily available sulfonylating reagents. The present method provides a novel strategy for generating nucleophilic sulfonyl sources using electrophilic sulfonyl chlorides as starting materials. Further sulfonyl chlorides-promoted sulfonylation reactions and their potential applications are currently underway in our laboratory.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules29122863/s1, Copies of the 1H NMR and 13C NMR spectra for compounds 3aa–3ta, 3xa and 3ab–3ao.

Author Contributions

W.Y., Z.-Y.T. and Y.-J.L. performed the experiments and analyzed the data. L.-Y.X. wrote the original draft and was responsible for reviewing and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the National Natural Science Foundation of China (22101082), the Science and Technology Innovation Program of Hunan Province (2022RC1119), and the construct program of applied characteristic discipline in Hunan Province.

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 conflicts of interest.

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Molecules 29 02863 sch001
Scheme 1. Deoxygenative C2-H sulfonylation of quinoline N-oxides with sulfonyl chlorides. (a) H-phosphonate-promoted deoxygenative C2-sulfonylation of quinoline N-oxides; (b) zinc-dust-mediated deoxygenative C2-sulfonylation of quinoline N-oxides; (c) CS2/Et2NH promoted deoxygenative C2-sulfonylation of quinoline N-oxides.
Scheme 1. Deoxygenative C2-H sulfonylation of quinoline N-oxides with sulfonyl chlorides. (a) H-phosphonate-promoted deoxygenative C2-sulfonylation of quinoline N-oxides; (b) zinc-dust-mediated deoxygenative C2-sulfonylation of quinoline N-oxides; (c) CS2/Et2NH promoted deoxygenative C2-sulfonylation of quinoline N-oxides.
Molecules 29 02863 sch001
Molecules 29 02863 sch002
Scheme 2. Preparation of 3aa–3xa. Conditions: 1 (0.3 mmol), 2a (0.6 mmol), CS2 (0.45 mmol), Et2NH (0.6 mmol), DCM (3 mL), air, rt, 15–30 min. Isolated yields are given based on 1.
Scheme 2. Preparation of 3aa–3xa. Conditions: 1 (0.3 mmol), 2a (0.6 mmol), CS2 (0.45 mmol), Et2NH (0.6 mmol), DCM (3 mL), air, rt, 15–30 min. Isolated yields are given based on 1.
Molecules 29 02863 sch002
Molecules 29 02863 sch003
Scheme 3. Preparation of 3ab–3aq. Conditions: 1a (0.3 mmol), 2 (0.6 mmol), CS2 (0.45 mmol), Et2NH (0.6 mmol), DCM (3 mL), air, rt, 15–30 min. Isolated yields are given based on 1a.
Scheme 3. Preparation of 3ab–3aq. Conditions: 1a (0.3 mmol), 2 (0.6 mmol), CS2 (0.45 mmol), Et2NH (0.6 mmol), DCM (3 mL), air, rt, 15–30 min. Isolated yields are given based on 1a.
Molecules 29 02863 sch003
Molecules 29 02863 sch004
Scheme 4. Gram-scale synthesis of 3aa.
Scheme 4. Gram-scale synthesis of 3aa.
Molecules 29 02863 sch004
Molecules 29 02863 sch005
Scheme 5. Control experiments.
Scheme 5. Control experiments.
Molecules 29 02863 sch005
Molecules 29 02863 sch006
Scheme 6. Possible mechanism.
Scheme 6. Possible mechanism.
Molecules 29 02863 sch006
Table 1. Optimization of reaction conditions a.
Table 1. Optimization of reaction conditions a.
Molecules 29 02863 i001
EntryR1R2R3NSolventRatios of 2a to 1aYield of 3aa %
1Et2NHTHF255
2Et2NHDCM267
3Et2NHDCE263
4Et2NHEtOAc242
5Et2NHAcetone20
6Et2NHCH3CN247
7Et2NHDMF224
8Me2NHDCM243
9IPr2NHDCM27
10morpholineDCM212
11piperidineDCM28
12Et2NHDCM20
13Et2NHDCM2.567
14Et2NHDCM366
15Et2NHDCM1.553
16 bEt2NHDCM279
17 cEt2NHDCM284
18 dEt2NHDCM282
19 eEt2NHDCM20
20noneDCM20
a Conditions: unless otherwise noted, 1a. (0.3 mmol, 1 eq), CS2 (0.36 mmol, 1.2 eq), R1R2R3N (0.45 mmol, 1.5 eq); 2a. solvent (3 mL), rt, 0.5 h, isolated yields were given. b Here, 2 equiv. of Et2NH was used. c Here, 1.5 equiv. of CS2 was used. d Here, 2 equiv. of CS2 was used. e The reaction proceeded in the absence of CS2.
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Yang, W.; Tian, Z.-Y.; Lin, Y.-J.; Xie, L.-Y. An Unexpected Synthesis of 2-Sulfonylquinolines via Deoxygenative C2-Sulfonylation of Quinoline N-Oxides with Sulfonyl Chlorides. Molecules 2024, 29, 2863. https://doi.org/10.3390/molecules29122863

AMA Style

Yang W, Tian Z-Y, Lin Y-J, Xie L-Y. An Unexpected Synthesis of 2-Sulfonylquinolines via Deoxygenative C2-Sulfonylation of Quinoline N-Oxides with Sulfonyl Chlorides. Molecules. 2024; 29(12):2863. https://doi.org/10.3390/molecules29122863

Chicago/Turabian Style

Yang, Wei, Zhong-Ying Tian, Ying-Jun Lin, and Long-Yong Xie. 2024. "An Unexpected Synthesis of 2-Sulfonylquinolines via Deoxygenative C2-Sulfonylation of Quinoline N-Oxides with Sulfonyl Chlorides" Molecules 29, no. 12: 2863. https://doi.org/10.3390/molecules29122863

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