Rhodium-Catalyzed Desymmetric Hydrosilylation Of 1,1-Disubstituted Cyclopropenes

Chiral organosilicon compounds are one of the most useful synthetic intermediates in organic chemistry.Since they display an important role in many chemical fields,such as organic synthesis,materials science,and medicinal chemistry,the synthesis of chiral organosilanes has received extensive attention in recent years.Transition metal catalyzed asymmetric hydrosilylation of olefins represent a straightforward approach toward the chiral organosilicons,it occupies the following advantages: simple operation system,high process efficiency,mild reaction condition,and less by-product formation.However,traditional hydrosilylations are limited to the use of terminal olefins,there is persistent need for the development of efficient catalytic systems for other types of olefin compounds such as polysubstituted olefins.In this respect,1,1-disubstituted cyclopropenes are employed as model substrates to develop highly efficient chiral Rh catalytic systems.We expected that these novel processes can complete the construction of a carbon quaternary stereocenter and carbon-linked silicon stereocenter via the one-step desymmetry process of prochiral cyclopropenes.The research results are summarized as follows:(1)A highly stereoselective desymmetric hydrosilylation of 1,1-disubstituted cyclopropenes has been accomplished for the first time.A series of potentially valuable chiral cyclopropyl organosilicon compounds bearing a carbon quaternary stereocenter was directly and efficiently constructed via the Rh/(R)-DTBM-Segphos-catalyzed desymmetric hydrosilylation of 1,1-disubstituted cyclopropenes(up to>99% ee,>99:1 dr).The enantioselectivity and diastereoselectivity of the derivatized products can be excellently maintained in the further investigation of cyclopropyl organosilicon compounds with two chiral centers.Furthermore,cyclopropanyl-functionalized silanols bearing two C-stereogenic centers or a quaternary carbon stereocenter can be accessed easily from the catalytic desymmetric hydrosilylation and one-pot oxidation by Rh catalysis.This methodology permit seversal advantages: easy-to-handle procedure,no intermediates isolation,high yield and stereoselective(up to 80% yield,98% ee,>99:1 dr).(2)Catalytic construction of silicon-stereogenic center was attempted based on rhodium-catalyzed desymmetric hydrosilylation of 1,1-disubstituted cyclopropenes using prochiral silanes.Prochiral silane was introduced into the asymmetric hydrosilylation reaction system of 1,1-disubstituted cyclopropenes.It was found that the carbon quaternary stereocenter can be constructed with high enantioselectivity,however,the construction of silicon-setereogenic center is extremely difficult via the one-step hydrosilylation reaction because the diastereoselectivity is poor(up to 80% yield,99% ee,52:48 dr),follow-up studies will be further optimized.In summary,we have achieved the first desymmetric hydrosilylation of 1,1-disubstituted cyclopropene and synthesized a series of highly stereoselective chiral cyclopropyl organosilicon compounds.Chiral cyclopropyl silanol compounds were approached in one step via the in-situ oxidation reaction.Furthermore,silicon chiral center was initially explored based on optimal conditions.