Shen Xiao group, Wuhan University: highly selective synthesis of trisubstituted alkenyl silicon compounds catalyzed by boron and nickel

Organosilicon compounds are widely used in synthetic chemistry and materials science The functional group substituted alkenyl silicon is an important kind of alkenyl silicon, because the functional group can be used for downstream transformation Therefore, alkenyl silicon substituted by thioether is a kind of compounds with potential application value Hydrosilylation of alkynylthioether is the most economical way to synthesize alkynylsilicon compounds However, the control of regioselectivity and stereoselectivity is the challenge of this method Shen Xiao group of Wuhan University first reported the highly selective β - anti selective hydrosilylation of alkynyl Sulfide Catalyzed by B (C6F5) 3 At the same time, the group applied the hydrosilylation products to the C-S bond cross coupling reaction catalyzed by Ni, and realized the stereospecific synthesis of a series of three substituted alkenylsilicon The results were published in the recent org Lett (org Lett 2020, 22, 3, 970-975) Prof Shen Xiao, Professor, doctoral supervisor In 2013, he graduated from Shanghai organic Research Institute (Tutor: researcher Hu Jinbo), and continued to work as a research assistant in Shanghai organic Research Institute for half a year From February 2014 to may 2015, he was engaged in postdoctoral research at Harvard University (Tutor: Professor Tobias Ritter), from June 2015 to July 2017, he continued to be engaged in postdoctoral research at Boston College (Tutor: Professor Amir H hoveyda), and then Professor Shen Xiao joined the Institute of higher studies at Wuhan University to carry out independent scientific research He has been a part-time professor of Engineering Research Center of Ministry of education of organosilicon compounds and materials since Selected by the youth thousand talents program of the Central Organization Department (the 14th batch), distinguished professor of Hubei youth Hundred Talents Program (the 8th batch), and "Hongyi youth scholar" of Wuhan University Frontier research achievements: boron and nickel catalysts are widely used in the field of materials and medicine for the highly selective synthesis of trisubstituted alkenes Alkenyl silicon can be polymerized into long-chain polymers containing silicon group in the main chain, which has an immeasurable prospect in the field of materials In addition, c-Si bond conversion of alkenyl silicon is an important means of synthesis science Because of the chemical transformation of functional groups, the synthesis value of alkenyl silicon directly connected with functional groups is particularly obvious In recent years, the chemical conversion of C-S bond has become a research hotspot However, the stereoselective synthesis of thioether substituted alkenyl silicon compounds is a challenge There are few successful examples of stereospecific coupling reactions involving alkenylthioether Recently, Shen Xiao's group has realized the boron catalyzed β - anti selective hydrosilylation of alkynylthioether, and then realized the stereospecific conversion of C-S bond to C-C bond through nickel catalysis Fig 1 Optimization of reaction conditions (source: org Lett.) the author first took phenylthioheptylene (1a) and diphenylsilane (2a) as template substrates, and selected AlCl3 (1.5 mol%) as catalyst, and the substrates basically did not convert The author thinks that the reason is that the coordination of the substrate and AlCl3 leads to the deactivation of the catalyst When the catalyst was increased to 120 mol%, the yield was 10% (entry 2) The author thinks that it is necessary to select a suitable catalyst to reduce its coordination with alkynyl sulfide and not to make it inactive After screening some catalysts, it is found that B (C6F5) 3 has a good catalytic effect and 85% yield (entry 8) Figure 2 Substrate expansion (source: org Lett.) in this paper, firstly, the substrate expansion of silane is carried out Whether it is a substituted silane, a disubstituted silane or a trisubstituted silane, it has very high universality, and it has very good applicability to functional groups (- Cl, - F, - OPH, - pH, - SiMe3, endoene, benzothiophene, etc.) The substrate alkynyl sulfide can be hydrogenated with primary silane twice to produce 3VA For the expansion of alkynyl sulfide, it has a very good reaction effect on electron donor group and neutral group For the electron absorption group-cf 3, the reaction yield is medium, especially for alkynyl sulfide of all alkanes, it still has a good yield and a single selective hydrosilylation product For the expansion of alkyl group, isopropyl group and n-butyl group all have excellent yield and single selectivity, but - pH and - TBU, which have larger steric hindrance of substituent group, have not got the product basically Due to the incompatibility of B (C6F5) 3 with - ome, when the substrate is o-methoxyphenylalkynyl sulfide, the product of demethylation hydrosilylation of benzo-7-membered ring is 3As Figure 3 Substrate expansion of Ni catalyzed conversion of C-S bond to C-C bond (source: org Lett.) the author uses Ni (DPPE) Cl 2 as catalyst, the product 3Y of hydrosilylation of alkynylthioether as substrate, and reacts with formant to convert C-S bond to C-C bond stereospecificity, with medium to good products and good universality (compatible with OME, - NME 2, - F , - Cl, - pH and alkyl) It reacts with cyclopropane form reagent to form a single selective product 4G It is worth noting that this kind of compounds are difficult to achieve a single selective synthesis by the hydrosilylation of dialkyl endoalkyne If methyl formant is used as raw material, it also has a high stereoselectivity of 92 / 8 Fig 4 Transformation of Si-H, c-Si, C-S bond (source: org Lett.) for the application of silicon-containing group transformation in synthesis science, the author also tried some transformations The product 3a is a desiliconized product 5 (85% yield) under the catalysis of [PD], and the conversion from Si-H bond to Si ome bond is 6 (85% yield) under the catalysis of IPR HCl In addition, the conversion from c-Si bond to C-C bond has been realized by two steps: 3A reacts with AGF first, and then cross coupling with iodoaromatic hydrocarbon under the catalysis of [PD] to produce product 7 (68% yield) In this paper, asymmetric trisubstituted all carbon alkenes 8,9 were synthesized with 7 as substrate and Ni as catalyst Fig 5 Mechanism study (source: org Lett.) the author also studied the mechanism of hydrogen silicification reaction In this paper, the product 10 of the reaction between B (C6F5) 3 and alkynyl sulfide was separated by crystallization and other steps The author found that alkynyl sulfide reacts with B (C6F5) 3 for 10 hours first, then with silane, only 7% yield can be obtained Therefore, it is speculated that by-product 10 is the main cause of catalyst deactivation, not the effective catalyst In reaction D, the author found that Si-H can be easily converted to si-d bond under the catalysis of B (C6F5) 3, so Si-H and si-d can not compete in the same reaction In this paper, we use ph2sih2 and ph2sid 2 to react with alkynylthioether in parallel, and find that their KIE is close to 1, suggesting that the reaction of Si-H bond is not the decisive step In the competitive reaction F, the substrate with electron deficient CL group for 1H is much lower than that without substituent group for 1a, suggesting that nucleophilic addition reaction is the decisive step of the reaction Figure 6 Mechanism prediction (source: org Lett.) the author proposed the possible reaction mechanism The Si-H bond is first coordinated with B (C6F5) 3, and then the Si-H bond is activated, which will generate a small amount of positive silicon ions It has a very fast speed for alkynylthioether to generate such ion pairs as I II and IV then, the negative hydrogen pair of B-H attacks the intermediate nucleophilic addition in the ion pair (this step is the decisive step) to generate the target product Another process can not be ruled out Intermediate I directly attacks thioalkyne to form intermediate V, and then forms ion pairs such as II and IV after s I-h bond is broken, so as to complete conversion and generate target products The related work was published in org Lett (DOI: 10.1021 / ACS Orglett 9b04505) The corresponding author of the paper is Professor Shen Xiao of higher Research Institute of Wuhan University The first author is Zhang Yunxiao, Ph.D., and Chen Yanran, M.A The research work was supported by NSFC, the youth thousand talents program of the Central Organization Department, the State Key Laboratory of life organic and Wuhan University At present, Shen Xiao's research group has 1 postdoctoral student, 5 doctoral students, 7 master's students and 2 research assistants The website of the research group is http://xiaoshen.whu.edu.cn/index.php The group welcomes young people who are passionate about organic chemistry to learn about and join in Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.