Indolizines. IV. Reductive cleavage of acyl groups from acetylindolizines. C-Protonation and fragmentation of Indolizine-3-carbinols

Abstract

Sodium borohydride in ethanol has effected cleavage of 3-acetylindolizines to indolizines in those cases where the intermediate 3-carbinols are readily protonated at C3. Reduction of 3-acetyl-2-methylindolizine in EtOD has demonstrated that fragmentation proceeds via C-protonation, and has also provided a selective method for the 3-deuteration of reactive indolizines. 1-Acetyl- and 1,3-diacetyl-indolizines gave unstable product mixtures on reduction excepting the one case where the product carbinol was stabilized by a resistant, electron-withdrawing 3-substituent. 3-Ethoxyoarbonyl groups were not affected.