The preparation of 3H-1,2-diazepine 2-oxides and their rearrangement to give 3-alkenyl-3H-pyrazole 2-oxides

Abstract

The oxidation of a range of monocyclic and fused 3H-1,2-diazepines (1a–d) with m-chloroperbenzoic acid gave the 2-oxides, e.g.(9)–(11). In one case the diazepine 2-oxide (5) rearranged readily at room temperature to give the 3-alkenyl-3H-pyrazole 2-oxide (16) in a ca. 1 : 1 equilibrium mixture with (5). The activation energy for ring inversion of the 3H-1,2-diazepine 2-oxides, determined by variable-temperature ¹³H n.m.r. spectroscopy, was ca. 12–16 kJ mol^–1 lower than that for the parent diazepines.