Retro-Ene Reactions in Heterocyclic Synthesis. III. A New Route to 4,5-Dihydrooxazoles and 5,6-Dihydro-4H-1,3-oxazines

Article abstract of DOI:10.1002/jhet.5570340224

Methyl (E)-4,4-dimethyl-5-oxo-2-pentenoate (1, X = O) reacted with 1,2- or 1,3-aminoalcohols 3 to yield oxazolidines 4a-c or tetrahydro-1,3-oxazines 4d,e. The corresponding imino ester 1 (X = NBu-t) also gave 4 on reaction with 3. Compounds 4 on heating at 230° yielded 4,5-dihydrooxazoles 5a-c or 5,6-dihydro-4H-1,3-oxazines 5d,e along with methyl 4-methyl-3-pentenoale (6).