Acid-catalysed rearrangement of 3-acyl-6-alkoxy-5,6-dihydro-4H-1,2-oxazines: a route to 3-alkoxypyridine 1-oxides

Abstract

6-Alkoxy-5,6-dihydro-4H-1,2-oxazines (2) and (5) have been prepared by the reaction of chloro oximes (1) with enol ethers in the presence of sodium carbonate. The 3-phenyloxazine (2) rearranges to the nitrone (3) in methanolic HCl. In contrast, the 3-acyloxazines (5a–e) are converted into 3-alkoxypyridine 1 -oxides (7) in aqueous alcoholic HCl. With HCl in acetic acid the oxazine (5a) is converted into 2-chloromethyl-3-hydroxypyridine hydrochloride (10a); analogous reactions take place with oxazines (5b) and (5d). Possible mechanisms for these reactions are discussed.