Stereoselective Synthesis of dl-Prosafrinine and dl-Pseudocarpamic Acid

The SnC12-effected carbon-carbon bond formation of endoperoxides was applied to alkyl substituted 1.2-dihydropyridines &-h to produce &-Q and ,@-& whose stereochemistry was clarified.Starting from & and &, , piperidine alkaloids, prosafrinine and pseudocarparnic acid were synthesized in racemic forms.Variously alkylated 1,2-dihydropyridine derivatives &-Q were synthesized by the 2 .reaction of alkylpyridines with either NaE.Hd1 or Grignard reagent in the presence of alkyichloroformates,and submitted to the sensitized photooxygenation reaction, followed by the SnC12-effected ring opening reaction with trimethylsilylated ketones and an en01 ether.3Formation of an isomeric pair of condensation products, 2 and $, was generally observed, one isomer being mostly predominant.In cases of 2 3