Rhodium‐Catalyzed Synthesis of Chiral Spiro‐9‐silabifluorenes by Dehydrogenative Silylation: Mechanistic Insights into the Construction of Tetraorganosilicon Stereocenters |
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| Authors: | Dr Masahito Murai Yutaro Takeuchi Kanae Yamauchi Dr Yoichiro Kuninobu Prof Dr Kazuhiko Takai |
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| Institution: | 1. Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan;2. Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan |
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| Abstract: | Mechanistic insight into the construction of quaternary silicon chiral centers by rhodium‐catalyzed synthesis of spiro‐9‐silabifluorenes through dehydrogenative silylation is reported. The C2‐symmetric bisphosphine ligand, BINAP, was effective in controlling enantioselectivity, and axially chiral spiro‐9‐silabifluorenes were obtained in excellent yields with high enantiomeric excess. Monitoring of the reaction revealed the presence of a monohydrosilane intermediate as a mixture of two constitutional isomers. The reaction proceeded through two consecutive dehydrogenative silylations, and the absolute configuration was determined in the first silylative cyclization. Competitive reactions with electron‐rich and electron‐deficient dihydrosilanes indicated that the rate of silylative cyclization increased with decreasing electron density on the silicon atom of the starting dihydrosilane. Further investigation disclosed a rare interconversion between the two constitutional isomers of the monohydrosilane intermediate with retention of the absolute configuration. |
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| Keywords: | asymmetric catalysis C− H activation rhodium silicon spiro compounds |
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