Highly Diastereoselective Alkylation of Chiral Tin(II) Enolates onto Cyclic Acyl Imines. An Efficient Asymmetric Synthesis of Bicyclic Alkaloids Bearing a Nitrogen Atom Ring Juncture.

An extremely short asymmetric synthesis of the 1-azabicyclic alkaloids involving pyrrolizidine, indolizidine, and quinolizidine skeletons is described. The key reaction used is a novel asymmetric alkylation of chiral tin(II) enolates of various 3-acyl-4 (S or R)-IPTTs onto cyclic acyl imines. This particularly mild alkylation procedure is highly general, exhibits high diastereoselectivity, and allows prediction of the absolute stereochemistry of the alkylation products