Short stereoselective synthesis of (+)-crispine A via an N-sulfinyl Pictet-Spengler reaction

We report the highly stereoselective synthesis of (R)-(+)-crispine A from the (R)-N-sulfinyl amine 1 by using a one-pot process involving the Pictet-Spengler reaction with 4-chlorobutanal, removal of the sulfinyl group by protonolysis of the N-S bond and in situ cyclization, with a 55% overall yield.