Allylstannation of N-acyliminium intermediates: a possible method for the stereocontrolled synthesis of polyhydroxypiperidines

The stereochemistry of the allylstannation of acyliminium intermediates has been examined for γ-alkoxyallyltins and γ-silyloxyallyltributyltins. In the latter case, the reaction has been shown to afford cleanly the syn adduct. Its subsequent ring-closing metathesis and dihydroxylation has allowed the highly stereoselective preparation of a 2-aryl-trihydroxypiperidine.