Enantioselective cyanosilylation of ketones catalyzed by double-activation catalysts with N-oxides |
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Authors: | Fu-Xue Chen Xiaoming Feng Guolin Zhang |
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Institution: | a Key Laboratory of Green Chemistry and Technology (Sichuan University), Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, China b Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China c Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China |
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Abstract: | Enantioselective addition of trimethylsilyl cyanide to ketones by a catalytic double-activation method is described. By combinatorially using 2.0 mol% of a chiral salen-titanium complex and 1.0 mol% of an achiral tertiary amine N-oxide, aromatic, aliphatic and α,β-unsaturated ketones are converted into corresponding cyanohydrin trimethylsilyl ethers with 50-93% yield and 59-86% ee. The effects of ligand structure, catalyst loading and substrate concentration, solvents, the nature of Lewis base, counter ion and other additives, temperature, and substrate structure on the enantioselectivity are discussed. Three possible paths to achieve the asymmetric version of double-activation catalysis and two independent examples of it are proposed. |
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Keywords: | Asymmetric catalysis Cyanohydrin Cyanosilylation Double-activation Ketone N-Oxide |
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