SYNTHESIS OF 6-ETHOXY-6H-1,2-OXAZINES BY HETERO-DIELS-ALDER REACTION OF 1-BROMO-2-ETHOXYETHENE WITH ALPHA-NITROSO ALKENES

A variety of 6H-1,2-oxazines 10 could efficiently be prepared by heter o Diels-Alder reaction of alpha-nitroso alkenes 2 with 1-bromo-2-ethox yethene (8) and consecutive elimination of HBr by DBU. Heterodienes 2 were generated in situ from alpha-halogen oximes 6. Primary cycloadduc ts 9 were isolated in singular cases, however, an attempt to substitut e bromide in 9e by an azido group gave the desired compound 11 only as minor component together with elimation product 10e. 6H-1,2-oxazines 10 are valuable precursors for addition reactions which open new synth etic possibilities.