Synthesis Studies toward Chloroazaphilone and Vinylogous γ-Pyridones: Two Common Natural Product Core Structures

Chloroazaphilone is a common structure found in a number of natural products. Reported herein
is a practical synthesis of a model chloroazaphilone that utilizes Pb(OAc)4 oxidation of HClO4/HOAc pyrinium salt in a key one-pot operation. Reaction of this chloroazaphilone with various
primary amines to afford the corresponding vinylogous γ-pyridones was also fully investigated.
The isolation of stable enamine intermediates provided direct evidence of reaction mechanisms.