Hetero analogs of alloxazines 3. Rearrangements of 6,8-dimethyl-9a-hydroxy-7,9-dioxo-9ah-6,7,8,9-tetrahydrodipyrimido[4,5-b][4′,5′-e][1,4]thiazines

The structures of 6,8-dimethyl-9a-hydroxy-7,9-dioxo-9aH-6,7,8,9-tetrahydrodipyrimido[4,5-b][4′,5′-e][1,4]thiazines were studied by NMR spectroscopy and mass spectrometry. The transformation of these compounds in solution in DMSO was investigated. A spiro structure of the resulting rearrangement products was established by means of 13C NMR spectroscopy.