Lewis-base-catalyzed cyanosilylation

Mukaiyama and co-workers have reported a high-yielding Lewis base-catalyzed cyanosilylation of aldehydes [79]. The procedure was applied to the cyanosilylation of 22 (Table 2). Treatment of 22 with... 

Fig. (10). A piKisible mechanism for tlie Lewis base-catalyzed cyanosilylation of 22.

Another example is the asymmetric cyanosilylation of aldehydes catalyzed by bifunctional catalyst 131.100 Compound 131 contains aluminum, the central metal, acting as a Lewis acid, and group X, acting as a Lewis base. The asymmetric cyanosilylation, as shown in Scheme 8-50, proceeds under the outlined... 

Silylated cyanohydrins have found considerable utility in the regioselective protection of p-qui-nones, as intermediates for the preparation of 3-amino alcohols and as precursors to acyl anion equivalents. Such compounds are typicdly prepared in high yield by either thermal or Lewis acid catalyzed addition of TMS-CN across the carbonyl group. This cyanosilylation has a variety of disadvantages and modified one-pot cyanosilylation procedures have been reported. - The carbonyl group can be regenerated by treatment with acid, silver fluoride or triethylaluminum hydrofluoride followed by base. ... 

In 2004, Feng et al. reported enantioselective cyanosilylation of ketones catalyzed by chiral organoaluminum complex 56 (Scheme 40) [72, 73]. Their strategy involves the simultaneous activation of electrophiles by chiral Lewis acid 56 and of nucleophiles (TMSCN) by achiral Lewis base 57. 

Recently, hydrocyanation and cyanosilylation reactions with other type of chiral aluminum complexes were reported. In 1999, Shibasaki and Kanai reported enantioselective cyanosilylation of aldehydes catalyzed by Lewis acid-Lewis base bifunctional catalyst (64a) [56, 57]. In this catalyst, aluminum center works as a Lewis acid to activate the carbonyl group, and the oxygen atom of the phosphine oxide works as a Lewis base to activate TMSCN. Asymmetric induction was explained by the proposed transition state model having the external phosphine oxide coordination to aluminum center, thus giving rise to pentavalent aluminum... 

To avoid the intrinsic instability of cyanohydrins and their silyl ether, Saa and coworkers reported catalytic asymmetric cyanophosphonylation reaction of aldehydes with commercially available diethyl cyanophosphonate [58]. In these works, Lewis acid-Lewis base bifunctional catalyst (65) prepared by mixing BI-NOLAM ligand with amino arms as Lewis base and Et2AlCl was found to work nicely (Scheme 6.46). Since a strong positive nonlinear effect was observed in this reaction, actual catalyst is in equilibrium with some oligomeric species of the aluminum complexes. Bifunctional catalyst (65) could also catalyze cyanosilylation of... 

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