Synthesis of 6-ethoxy-6H-1,2-oxazines by hetero Diels-Alder reaction of 1-bromo-2-ethoxyethene with α-nitroso alkenes

A variety of 6H‐1,2‐oxazines 10 could efficiently be prepared by hetero Diels–Alder reaction of α‐nitroso alkenes 2 with 1‐bromo‐2‐ethoxyethene (8) and consecutive elimination of HBr by DBU. Heterodienes 2 were generated in situ from α‐halogen oximes 6. Primary cycloadducts 9 were isolated in singular cases, however, an attempt to substitute bromide in 9e by an azido group gave the desired compound 11 only as minor component together with elimination product 10e. 6H‐1,2‐oxazines 10 are valuable precursors for addition reactions which open new synthetic possibilities.