Synthesis and thermal reaction of pyridinium 3,3-diacyl-1-benzoylallylides [3,3-diacyl-1-benzoyl-1-(1-pyridinio)prop-2-enides]: formation of indolizine derivatives

Abstract

Pyridinium 3,3-diacyl-1-benzoylallylides [(IIIa–e), (IV), and (V)] are prepared by the reaction of pyridinium phenacylides with 2,2-diacyl-1-ethoxyethylenes. Refluxing compounds (IIIa), (IIIb), and (IV) in xylene provides 1-acyl-3-benzoylindolizines [(VI), (VII), and (IX)] in poor yields; similar treatment of the 2-methyl-pyridinium congeners (IIIc–e) affords 1,3-diacetyl-2-phenylindolizines [(X)–(XII)], accompanied by small amounts of 1-acetyl-3-benzoylindolizines [(VI)–(VIII)].