Highly Stereospecific Cyclizations of Homoallylic Silanols.

We demonstrate that di--butylsilanols are competent nucleophiles for the intramolecular interception of palladium π-allyl species. In these reactions, allyl ethyl carbonates are the best precursors for the formation of palladium π-allyl intermediates, and [(Cinnamyl)PdCl]/BINAP is superior to other Pd salt/ligand framework combinations. Our optimized protocol is compatible with a variety of silanol substrates. Importantly, the cyclization is perfectly stereospecific, proceeding via an - mechanism, which stands in contrast to reported analogous reactions of alcohols and phenols, known to proceed via an - mechanism. The alkenes in the product dioxasilinanes serve as blank slates for further functionalization.