New cascade transformations of 3-(2-aminophenyl- amino)-5,5-dimethyl-2-cyclohexen-1-one

The reaction of 3-(2-aminophenylamino)-5,5-dimethyl-2-cyclohexen-1-one with alloxan results in 3,3-dimethyl-1,2,3,4,10,11-hexa- hydrospiro(1H-dibenzo[b,e][1,4]diazepine)-11,5’-pyrimidine-1,2’,4’,6’-tetraone or N-aminocarbonyl-1-(2-aminophenyl)-3-hydroxy- 6,6-dimethyl-2,4-dioxo-2,3,4,5,6,7-hexahydro-1H-indole-3-carboxamide. The latter undergoes isomerization on dissolution in DMSO or DMF to give 5-[2-(2-aminophenylamino)-4,4-dimethyl-6-oxocyclohexenyl]-5-hydroxypyrimidine-2,4,6(1H,3H,6H)-trione, thus demonstrating a new example of ring–ring tautomerism.