Intramolecular reactions of N-nitrenes: oxidation of 3-amino-2-(2,4-dimethoxyphenylethyl)quinazolin-4(3H)-ones

Abstract

Oxidation of the N-aminoquinazolones (5) and (6) gave the 1 H-azepines (7) and (10) respectively. Boat-to-boat flipping of the azepine ring in compound (7) is slow on the n.m.r. time-scale even at 140 °C. Heating of compound (10a) in chlorobenzene at 135 °C brings about interconversion with the stereoisomer (10b) with a minimum free energy barrier of 30 kcal mol^–1. Possible reasons for this high barrier to azepine ring inversion are examined.