Stereoselective Synthesis of 2,3,6-Trisubstituted Tetrahydropyridines via Tf2O-Mediated Grob Fragmentation: Access to Indolizidines (−)-209I and (−)-223J
摘要:
Herein we describe the gamma-amino hydroxide Grob fragmentation of the aza-bicyclo[2.2.2]octene 1 using triflic anhydride as the activating agent. The resulting dihydropyridinium ion can react with a wide variety of Grignard reagents, giving access to 2,3,6-trisubstituted tetrahydropyridines (2) with high regio- and stereoselectivities. This methodology has been applied to the short synthesis of natural indolizidines (-)-2091 (3) and (-)-223J (4).