Sequential deprotection–cyclisation reaction: stereoselective synthesis of azabicyclic β-enamino ester derivatives and (−) indolizidine 209D

This paper describes a new strategy for the stereoselective synthesis of pyrrolizidine and indolizidine based enamino esters and their acyl derivatives from l-proline. The key reaction in this process involves deprotection followed by ring closure of cyclic N-Boc amino-β-ketoesters. Also, the synthesis of 5R,9R-(−)-indolizidine 209D has been accomplished using this protocol.