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Proceeding Paper

New in the Catalytic Synthesis of Practically Important Eight- and Nine-Membered Carbocycles by Cycloaddition Reactions with the Participation of 1,3,5-Cycloheptatrienes and 1,3,5,7-Cyclooctatetraenes †

by
Gulnara N. Kadikova
* and
Usein M. Dzhemilev
Institute of Petrochemistry and Catalysis of Russian Academy of Sciences, 141 Prospekt Oktyabrya, 450075 Ufa, Russia
*
Author to whom correspondence should be addressed.
†
Presented at the 2nd International Electronic Conference on Catalysis Sciences—A Celebration of Catalysts 10th Anniversary, 15–30 October 2021; Available online: https://eccs2021.sciforum.net/.
Chem. Proc. 2022, 6(1), 2; https://doi.org/10.3390/ECCS2021-11037
Published: 14 October 2021
(This article belongs to the Proceedings of The 2nd International Electronic Conference on Catalysis Sciences—A Celebration of Catalysts 10th Anniversary)
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Abstract

:
The data obtained by the authors in the field of chemistry of 1,3,5-cycloheptatrienes and 1,3,5,7-cyclooctatetraenes with the participation of complexes of transition metals are summarized. The reactions of cyclocodimerization of 1,3,5-cycloheptatrienes and 1,3,5,7-cyclooctatetraenes with alkenes, dienes and alkynes in the presence of transition metal complexes, carried out by the type of [6π + 2π]- and [4π + 2π]-cycloaddition, are considered. Special attention is paid to the application of these reactions in the synthesis of practically important bi-, tri- and polycyclic strained compounds, as well as in the development of stereoselective methods for the synthesis of natural compounds.

1. Introduction

Among the large number of possible ways of constructing medium cycles, the most preferred are those based on cycloaddition reactions using metal complex catalysis methods [1,2,3]. Classical ring-closure methods are effective for small ring systems, but problematic for medium-sized ring systems owing to entropic and transannular penalties incurred when bringing the two ends of a reactant together [4]. For this reason, significant advances in the design of medium cycles have been achieved through new cycloaddition reactions catalyzed by transition metal complexes [1,2,3].
The development of reactions of catalytic cycloaddition with obtaining medium cycles is one of the most urgent and demanded areas of modern organic synthesis, in view of the high prevalence of these compounds in the composition of a large number of biologically active substances and drugs [1]. For example, eight-membered carbocycles form the structural backbone of a number of important medicinal compounds (Figure 1). Currently, the natural compound taxol is an effective anticancer agent widely used in medical practice [5]. In 2008, pleuromutilin was approved as an antibacterial drug [6].
According to the analysis of the world literature, one of the promising directions in the synthesis of medium cycles is directed catalytic conversions of available cyclic polyunsaturated monomers—1,3,5-cycloheptatrienes (CHT) and 1,3,5,7-cyclooctatetraene (COTT) [3]. Catalytic cycloaddition reactions involving these cyclopolyenes lead to the formation of practically important eight-membered carbocycles, bicyclo[4.2.1]nonadi(tri)enes and bicyclo[4.2.2]decatri(tetra)enes [1,2,3]. The bicyclo[4.2.1]nonane skeleton is a key structural element of biologically active terpenoids with pronounced antitumor properties [7,8,9] (Figure 2).
In the literature, there are preferably publications devoted to the study of reactions of thermally and photochemically induced cycloaddition of alkenes, 1,2-, 1,3-dienes and alkynes to Fe-, Ru- and Cr-containing carbonyl complexes CHT [10,11,12,13,14]. The catalytic variants of these transformations are represented by Ti-, Co-, Cr-, Mo- and Rh-catalyzed cyclodimerization of CHT [15,16,17,18,19,20,21].

2. Results and Discussion

To date, we have accumulated significant experience in the development of effective one-pot methods for the synthesis of various classes of previously undescribed bi-, tri- and polycyclic compounds based on cycloaddition reactions CHTs and COTT catalyzed by complexes of transition metals [3]. As a result of research carried out over the past 5–10 years, we have proposed effective preparative methods for the synthesis of a wide range of substituted bicyclo[4.2.1]nona-2,4-dienes and bicyclo[4.2.1]nona-2,4,7-trienes based on reactions of titanium- and cobalt-catalyzed cycloaddition of 1,2-dienes and alkynes to CHT and its derivatives. So, in 2013, we developed a two-component catalytic system TiX2Cl2-Et2AlCl (X = Cl, acac, i-PrO), which was used for the first time in the [6π + 2π] cycloaddition of 1,2-dienes 2 to CHT and 7-alkyl(phenyl,allyl)-1,3,5-cycloheptatrienes 1 to form substituted bicyclo[4.2.1]nona-2,4-dienes 3 as a single regioisomer [22] (Scheme 1).
In the development of research on the synthesis of new bicyclo[4.2.1]nonanes, as well as in order to expand the scope of application of the developed titanium-containing catalytic system, we carried out the cyclocodimerization of CHTs with alkynes [23]. It was found that [6π + 2π] cycloaddition of nitrogen- 4 and silicon-containing alkynes 5 to CHTs 1 under the action of the Ti(acac)2Cl2-Et2AlCl catalytic system in benzene for 8–24 h at 80 °C leads to the formation of bicyclo[4.2.1]nona-2,4,7-trienes 6 (61–88%) and 7 (79–88%) (Scheme 2):
Of particular interest are the works [24,25] on the reactions of cyclocodimerization of bis(1,3,5-cycloheptatriene-7-yl)alkanes—monomers containing in their structure simultaneously two cycloheptatriene fragments, which means two reaction centers. We found that as a result of the interaction of bis(1,3,5-cycloheptatriene-7-yl)alkanes 8 with a twofold excess of 1,2-dienes 2 or Si-containing alkynes 5 under the action of the catalytic system Ti(acac)2Cl2-Et2AlCl (benzene, 12 h, 80 °C) the corresponding [6π + 2π] cycloadducts are formed—bis(bicyclo[4.2.1]nona-2,4-diene)alkanes 9a,b and bis(bicyclo[4.2.1]nona-2,4,7-triene)alkanes 10a,b [24,25] (Scheme 3):
In 2019, we studied the cyclocodimerization reactions of 1-substituted CHTs [26]. We found 1-methyl(benzyl)-1,3,5-cycloheptatrienes 11 enter into a [6π + 2π]-cycloaddition reaction with Si-containing alkynes 5 under the action of the catalytic system Ti(acac)2Cl2-Et2AlCl (5 mol% Ti(acac)2Cl2, Ti/Al = 1:20, C6H6, 80 °C, 8 h) to form substituted bicyclo[4.2.1]nona-2,4,7-trienes 13 as a single regioisomer. Similarly, under the developed conditions (15 mol% Ti(acac)2Cl2, Ti/Al = 1:20, C6H6, 80 °C, 8 h), we managed to carry out the cyclodimerization of 1-methylcycloheptatriene 11 with propargylamines 4 to obtain nitrogen-containing bicyclo[4.2.1]nona-2,4,7-trienes 14 in high yields (76–88%) [26] (Scheme 4).
The reaction of 1-substituted CHTs 11 with terminal alkynes 12 takes place in the presence of a three-component cobalt-containing catalytic system Co(acac)2(dppe)/Zn/ZnI2 with the formation of functionally substituted bicyclo[4.2.1]nona-2,4,7-trienes 15, 16 as two regioisomers (72–86%) (Scheme 4).
In the development of ongoing studies on the synthesis of middle cycles based on cyclocodimerization of cyclic polyenes with unsaturated compounds of various structures, as well as with the aim of developing effective preparative methods for the synthesis of new classes of bicyclo[4.2.2]decatri(tetra)enes, we paid attention to COTT. In 2015, for the first time, we carried out the [6π + 2π]-cycloaddition of 1,2-dienes to COTT in the presence of a four-component catalytic system CoI2/dppe/Zn/ZnI2 with the formation of substituted (E)-bicyclo[4.2.2]deca-2,4,7-trienes 17 in high yields (76–87%) [27] (Scheme 5).
It should be emphasized that [6π + 2π]-cycloadducts of COTT with alkynes—bicyclo[4.2.2]deca-2,4,7,9-tetraenes are widely used as key synthons in the preparation of practically valuable natural and synthetic biologically active compounds [28,29,30,31]. For this reason, the creation of highly efficient methods for the synthesis of bicyclo[4.2.2]deca-2,4,7,9-tetraenes is especially urgent and in demand. To accomplish this task, we have developed an effective catalytic system—Co(acac)2/dppe/Zn/ZnI2, using which we have synthesized a wide range of functionally substituted bicyclo[4.2.2]deca-2,4,7,9-tetraenes 18–20 based on the reaction of [6π + 2π]-cycloaddition of alkynes and 1,3-diynes to COTT [28,32] (Scheme 6):

3. Conclusions

Thus, in the course of our studies, we have developed effective one-pot methods for the synthesis of a large assortment of previously undescribed and hard-to-reach functionally substituted bicyclo[4.2.1]nonadi(tri)enes and bicyclo[4.2.2]decatri(tetra)enes, which can act in as key precursors in the synthesis of modern drugs and valuable biologically active compounds.

Author Contributions

Conceptualization, U.M.D. and G.N.K.; methodology, validation, and execution of chemistry experiments, G.N.K.; manuscript preparation, U.M.D. and G.N.K. All authors have read and agreed to the published version of the manuscript.

Funding

The work was done within approved plans for research projects at the IPC RAS State Registration No. AAAA-A19-119022290008-6 (2019–2021), Grant of Russian Foundation for Basic Research (19-03-00393).

Acknowledgments

The structural studies of the synthesized compounds were performed with the use of Collective Usage Centre “Agidel” at the Institute of Petrochemistry and Catalysis of RAS.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Natural products with eight-membered carbocyclic skeletons.
Figure 1. Natural products with eight-membered carbocyclic skeletons.
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Figure 2. Natural products with the bicyclo[4.2.1]nonane core.
Figure 2. Natural products with the bicyclo[4.2.1]nonane core.
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Scheme 1. Cycloaddition of 1,2-dienes with CHTs.
Scheme 1. Cycloaddition of 1,2-dienes with CHTs.
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Scheme 2. Cycloaddition of alkynes with CHTs.
Scheme 2. Cycloaddition of alkynes with CHTs.
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Scheme 3. Cycloaddition of alkynes and 1,2-dienes with bis(1,3,5-cycloheptatriene-7-yl)alkanes.
Scheme 3. Cycloaddition of alkynes and 1,2-dienes with bis(1,3,5-cycloheptatriene-7-yl)alkanes.
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Scheme 4. Cycloaddition of alkynes with CHTs.
Scheme 4. Cycloaddition of alkynes with CHTs.
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Scheme 5. Cycloaddition of 1,2-dienes with COTT.
Scheme 5. Cycloaddition of 1,2-dienes with COTT.
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Scheme 6. Cycloaddition of alkynes with COTT.
Scheme 6. Cycloaddition of alkynes with COTT.
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Kadikova, G.N.; Dzhemilev, U.M. New in the Catalytic Synthesis of Practically Important Eight- and Nine-Membered Carbocycles by Cycloaddition Reactions with the Participation of 1,3,5-Cycloheptatrienes and 1,3,5,7-Cyclooctatetraenes. Chem. Proc. 2022, 6, 2. https://doi.org/10.3390/ECCS2021-11037

AMA Style

Kadikova GN, Dzhemilev UM. New in the Catalytic Synthesis of Practically Important Eight- and Nine-Membered Carbocycles by Cycloaddition Reactions with the Participation of 1,3,5-Cycloheptatrienes and 1,3,5,7-Cyclooctatetraenes. Chemistry Proceedings. 2022; 6(1):2. https://doi.org/10.3390/ECCS2021-11037

Chicago/Turabian Style

Kadikova, Gulnara N., and Usein M. Dzhemilev. 2022. "New in the Catalytic Synthesis of Practically Important Eight- and Nine-Membered Carbocycles by Cycloaddition Reactions with the Participation of 1,3,5-Cycloheptatrienes and 1,3,5,7-Cyclooctatetraenes" Chemistry Proceedings 6, no. 1: 2. https://doi.org/10.3390/ECCS2021-11037

APA Style

Kadikova, G. N., & Dzhemilev, U. M. (2022). New in the Catalytic Synthesis of Practically Important Eight- and Nine-Membered Carbocycles by Cycloaddition Reactions with the Participation of 1,3,5-Cycloheptatrienes and 1,3,5,7-Cyclooctatetraenes. Chemistry Proceedings, 6(1), 2. https://doi.org/10.3390/ECCS2021-11037

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