A highly enantioselectivecyanosilylation of ketones was developed by using a chiral lithium(I) phosphoryl phenoxide aqua complex as an acid/base cooperative catalyst. The pentacoordinate silicate generated in situ from Me3SiCN/LiCN acts as an extremely reactive cyano reagent. Described is a 30 gram scale reaction and the synthesis of the key precursor to (+)‐13‐hydroxyisocyclocelabenzine.
Effective Activation of the Chiral Salen/Ti(OiPr)4 Catalyst with Achiral PhenolicN-Oxides as Additives in the Enantioselective Cyanosilylation of Ketones
the asymmetric cyanosilylation of ketones. By using 10 mol % of chiral salen-titanium(IV) complex in combination with 1 mol% achiral phenolic N-oxide as an additive, aromatic, aliphatic and heterocyclic ketones have been converted into the corresponding cyanohydrin trimethylsilyl ethers in 58-96% yields with 56-82% ee. Several factors concerning the reactivity and enantioselectivity have been discussed
A novel C2-symmetric chiralN,N′-dioxide titanium complex was described, which could efficiently catalyze the asymmetric cyanosilylation of ketones in high yields with up to 92% ee under mild conditions. In addition, the catalyst system was simple and the ligands could be easily prepared from commercially available chiral amino acid.
An efficient and optically active, bifunctional tetraaza ligand (2S)-N-(1R,2R)-2-[(S)-pyrrolidine-2-carboxamido]-1,2-diphenylethyl}pyrrolidine-2-carboxamide has been developed for the addition of trimethylsilyl cyanide (TMSCN) to ketones. The bifunctionalcatalyst system based on a monometallic titanium complex was found to be a highly enantioselectivecatalyst to provide O-TMS cyanohydrins with up
A new bifunctional catalytic system based on chiral N-oxide titanium complexes has been used for the asymmetric cyano-silylation of ketones. Screening of a variety of chiral N-oxide metal complexes resulted in (1R,2S)-1-(2'-pyridylmethyl)-2-(diphenylhydroxymethyl)pyrrolidine N-oxide titanium complex, which gave O-TMS cyanohydrins in good yields with enantiomeric excesses of up to 69%. A catalytic cycle