FACILE AND CONVENIENT SYNTHESIS OF 2,6-DISUBSTITUTED 4H-1,3-OXAZIN-4-ONE DERIVATIVES

Facile and convenient methods for the preparation of a variety of 2,6- disubstituted 4H-1,3-oxazin-4-ones 3 by three complementary methods ar e described. Treatment of the branched aliphatic imidate 2c,d with dik etene 1 in the presence of a catalytic amount of acetic acid affords 2 -substituted 6-methyl-1,3-oxazin-4-ones 3c,d, whereas the unbranched i midate 2b,e gave oxazines 3b,e and pyrimidines 4b,e (Method A). The re action of acyl Meldrum's acid 5 with imidate 2 afford 2,6-disubstitute d oxazine 3, though the alkylimidate with acetyl Meldrum's acid yielde d 3 and 5-acetyl-1,3-oxazine-4,6-dione 8 (Method B). The cyclodehydrat ion of acylacetylcarboxamide 13 with acid, such as 70% perchloric acid or fluorosulfonic acid, afforded 1,3-oxazines 3 (Method C).