Ring enlargement reactions of tetramic acid derivatives

The 4-hydroxypyridones 7 and 3-hydroxypyridones 8/9 (azagrevellins) were pr epared by reaction of the pyrrolidinetrione 4 and diazoalkanes. The ring en largement proceeded by anionotropic [1,2]-rearrangement introducing carbon between C-3 and C-4 or, to a lesser extent, between C-2 and C-3 due to the different migration aptitudes of the two acyl groups involved. In a cognate manner ring expansion between C-2 and C-3 occured by the interaction of di azomethane and the pyrrolidinetrione hydrazone 15, to give the spiroepoxide 16 as the: final product. From the reaction of trione 4 and diazomethane, however, the diepoxide 14 was obtained. In this case ring homologation must have taken place by insertion of carbon between C-4 and C-5. In a two step ring expansion the pyridones 21 and 22 were obtained from the maleineimide s 17.