HETERO-DIELS-ALDER REACTION OF ETHYL 2-NITROSOACRYLATE AND CYCLOHEXADIENES,AND BROMINE INDUCED DIENE ISOMERIZATION

摘要

Bicyclic 8a-methoxy-1,2-oxazine (3a) and bicyclic 7-methoxy-1,2-oxazine (3b) were prepared via Hetero-Diels-Alder reaction between l-methoxy-l,4-cyclohexadiene (2a) and ethyl 2-nitrosoacrylate generated in situ from ethyl bromopyruvate oxime (1).The formation of 3b was ascribed to bromine,released from 1,which induced transformation of 2a to l-methoxy-1,3-cyclohexadiene (2b).3b could be easily transformed to oxazinone (3c) in CHCl_3,or other organic solvents in the presence of a trace amount of acid.