ORGANOLANTHANIDE CATALYSIS OF A MUKAIYAMA ADDITION-REACTION

Bis[bis(1,3-trimethylsilyl)cyclopentadienyl]-ytterbium(III) chloride, Cp''2YbCl, 2, is an effective catalyst in the presence of additional trimethylsilyl chloride for the reaction of silyl ester enolates, such as the trimethylsilyl enolate of methyl isobutyrate, 1, with aliphatic and aromatic aldehydes, to yield beta-silyloxy esters. The reaction shows good diastereoselection that is readily rationalized with a cyclic transition-state mechanism in which a key feature is the important role played by restricted coordination space around the lanthanide cation.