Alkyl esters were reduced with 1BU2AIH or a 1:1 mixture of 1BU2AIH and 1Bu3AI (iBu2AlH-iBu3Al or 1BU5AI2H), followed by trapping of the resulting tetrahedral intermediate with TMS-imidazole to produce monosilyl acetals. Reaction of the mixed acetals with allyltrimethylsilane in the presence of Lewis acids (Hosomi-Sakurai reaction) generated homoallylic alcohols or ethers selectively, depending on the substitution of the monosilyl acetal. TMS methoxy acetals (MeO—CH—OTMS) and TMS ethoxy acetals bearing additional complexing groups such as MeO- or Ph2C=N- provided alcohols with 1.5:1-9:1 threoselectivity, while simple TMS ethoxy acetals provided only ethyl ethers as products. The monosilyl acetal configuration was easily epimerized or racemized, and the configuration of the Hosomi-Sakurai product was apparently independent of the initial monosilyl acetal reactant configuration.
ASJC Scopus subject areas
- Organic Chemistry