1, 3-Oxazines and Related Compounds. XIII. Reaction of Acyl Meldrum's Acids with Schiff Bases Giving 2, 3-Disubstituted 5-Acy1-3, 4, 5, 6-tetrahydro-2H-1, 3-oxazine-4, 6-diones and 2, 3, 6-Trisubstituted 2, 3-Dihydro-1, 3-oxazin-4-ones

Abstract

The reactions of Schiff bases (2) with various acyl Meldrum's acids (1) were investigated. Refluxing of 1 and 2 in benzene caused an exchange reaction of the acetone moiety of 1 with the Schiff base moiety through the intermediate acylketenes 11 formed in situ from 1 to give 2, 3-disubstituted 5-acy1-3, 4, 5, 6-tetrahydro-2H-1, 3-oxazine-4, 6-diones (3). The oxazindiones 3 underwent thermal conversion to afford 2, 3, 6-trisubstituted 2, 3-dihydro-1, 3-oxazin-4-ones (4) in good yield. The intermediates 11 were found to be formed by thermal cleavage of both 1 and 3.