Heterocyclic syntheses with malonyl chloride. Part 12. Confirmatory and revisionary evidence for structures of products derived from 2-alkyl-(or -aryl-)thio-7-chloropyrano[3,4-e][1,3]oxazine-4,5-diones

Abstract

The structures previously proposed for the title compounds and various of their transformation products, have now been confirmed by ¹³C n.m.r. spectroscopy with one exception. For the products thought to be S-alkyl or -aryl (6-chloro- and -benzylamino-3-alkoxycarbonyl-2-oxopyran-4-yl)thiocarbamates, O-alkyl or -aryl (6-chloro- and -benzylamino-3-S-alkoxythiocarbonyl-2-oxopyran-4-yl)carbamate structures are now proposed on the basis of the chemical shift of the carbon bearing the S-alkoxy-group. A possible mode of formation of the products is outlined.