1,3-Oxazines and related compounds. XIII. Reaction of acyl Meldrum's acids with Schiff bases giving 2,3-disubstituted 5-acyl-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.

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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.

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