Dioxopyrrolines. XLIV. : Thermal 1, 3-Shift of 2-Azabicyclo[3.2.0]hept-2-ene Ring System : A New Entry to 3, 4-Dihydropyridines and 2-Azanorborn-2-enes

Abstract

Thermolysis of 4-oxo-2-azabicyclo[3.2.0]hept-2-enes caused two reactions; one is the 1, 3-shift of the C₁-C₇ bond to the C₃ carbon followed by cheletropic loss of CO from the intermediary formed 2-azanorborn-2-enes to yield the dihydropyridines, and the other is epimerization of the C₇-substituent. These two reactions occurred competitively depending on the nature of the C₇ substituent. Intermediary formation of the 2-azanorborn-2-enes in the rearrangement reaction was proved by trapping experiments with the use of 4-acetoxy derivatives. The mechanisms of the thermal 1, 3-shift and 7-epimerization are discussed.