Methyl enantioselective cyanosilylation

Corey reported a catalytic enantioselective cyanosilylation of methyl ketones using combination of a chiral oxazaborolidinium and an achiral phosphine oxide, [Eq. (13.23)]. An intermolecular dual activation of a substrate by boron and TMSCN by the achiral phosphine oxide (MePh2PO) is proposed as a transition-state model (54). The same catalyst was also used for cyanosilylation of aldehydes ... 

The subsequent study revealed that the chiral BLA (2b) is a potent chiral Lewis acid for enantioselective cyanosilylation of methyl ketones promoted by TMS cyanide and diphenylmethyl phosphine oxide as coreactants (to generate Ph2MeP(OTMS)(N=C as a reactive intermediate) (Scheme 1.4) [6]. The rational for the observed face selectivity can be explained by a transition state assembly in... 

Scheme 1.4 Enantioselective cyanosilylation of methyl ketones catalyzed by (2b).

Cyanosilylation of methyl ketones has been carried out using diphenylmethylphos-phine oxide and trimethylsilyl cyanide, generating a phosphorus isonitrile-type species, Ph2MeP(OTMS)(N=C ), as the reactive intermediate.271 A chiral oxazaborolidinium ion catalyst renders the reaction enantioselective. 

Chiral oxazaborolidinium ion is an excellent catalyst for the cyanosilylation of methyl ketones promoted by cyanotrimethylsilane and diphenylmethyl phosphine oxide (eq 27). Chiral thiourea (eq 28) and amino acid salt (eq 29) have been developed and employed as catalysts in the enantioselective s)m-thesis of cyanohydrins and their derivatives. 

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