Oxidative and Thermal Routes to Novel Isoxazolopyridines

Abstract

The novel bicyclic compounds isoxazolo [3,4-b] pyridine (1). 3-phenylisoxazolo [3,4- b] pyridine (2) and 3-phenylisoxazolo[3,4-c]pyridine (3) have been synthesized by oxidative cyclization of the amines 2-aminopyridine-3-carbaldehyde (4), (2-amino-3-pyridyl)phenylmethanone (5) and (3-amino-4-pyridyl)phenylmethanone (6). The oxidant was bis(acetato-O)phenyliodine. 3-Phenylisoxazolo[3,4-c]pyridine (3) was also obtained by thermolysis of 3-azido-4-benzoylpyridine (7). Comparison of the rate of thermolysis of this azide with that of 3-azidopyridine identified a neighbouring group effect (from the benzoyl group) which is about four times as large as in a corresponding 2-azidobenzophenone. COSY and HETCOR techniques have been used to assign the ¹H and ¹³C n.m.r. spectra of isoxazolo[3,4-b]pyridine (1).