Formation of pyridazino[6,1-c][1,4]oxazin-8(7H)-ones by intramolecular cycloaddition of azoalkenes

Abstract

The hydrazides (3) and (4) of 2-allyloxyalkanoic acids (1) and of prop-2-ynyloxyacetic acid have been prepared. These hydrazides have then been converted into the hydrazones (6) and (7), respectively, by reaction with phenacyl chloride. The azoalkenes have been generated from the hydrazones by reaction with sodium carbonate. The products isolated were the pyridazino-oxazinones (8)[from (6)] and (9)[from (7)], formed by spontaneous intramolecular cycloaddition reactions of the azoalkenes. The hydrazones (6b) and (6c) with asymmetric carbon centres adjacent to the carbonyl groups each gave mixtures of diastereoisomeric oxazines but there was considerable selectivity (6 : 1) in each case. This is ascribed to steric effects in the transition states. An analogous series of conversions has been carried out with the hydrazones derived from the hydrazides (3) and (4) and ethyl bromopyruvate. N-Acetyl-N-allyiglycine hydrazide (11) has also been prepared. The hydrazones (13) formed from this hydrazide and phenacyl chloride was converted by reaction with sodium carbonate into an azoalkene which cyclised to give the pyrazino[1,2-b] pyridazin-8-one (14a).