Ring Enlargement Reactions of Tetramic Acid Derivatives

摘要

The 4-hydroxypyridones 7 and 3-hydroxypyriones 8/9(azagrevellins)were prepared by reaction of the pyrrolidinetrione 4 and diazoalkanes. The ring enlargement proceeded by aniotropic[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 in volved. In a cognate manner ring expansion wetween C-2 and C-3 occured by the interaction of diazomethane and the pyrrolidinetrione hydrazone 15, to give the spiroepoxide 16 as the final product. From the reaction of trone 4 and diazomethane, however, the diepoxide 14 was obtained. In this case ring homologation must have taken place by insertion of carbo between C-4 and C-5. In a two step ring expeansion the pyridones 21 ans 22 were obtained from the maleineimides 17.