The intramolecular cycloaddition of azides with ω-chloroalkenes. A facile route to (±)-swainsonine and other indolizidine alkaloids

A potentially general route to the 1-azabicyclon.m.O]alkane skeleton of various alkaloids is embodied in the intramolecular 1,3-dipolar cycloaddition of aliphatic azides with ω-chloroalkenes. Cycloaddition is followed by rearrangement and intramolecular N-alkylation, affording bicyclic iminium ions1 in one operation. The application of this method to the synthesis of (±)-δ-coniceine6, (1S,2R,8aR)-indolizidine-1,2-diol13 and (−)-swainsonine15 is described.