Heating of the N-(3-oxo-1-cyclohexene-1-yl)-α-(methylsulfinyl) acetamides 7a-c with p-toluenesulfonic acid in 1, 2-dichloroethane gave the 3, 5, 6, 7-tetrahydro-3-methylthio-1H-indole-2, 4-diones 9a-c. Compound 9b, when heated in 85% phosphoric acid at 80°C, underwent further cyclization to afford the 7-(methylthio) erythrinan-1, 8-dione 14 and the 6, 7-didehydroerythrinan-1, 8-dione 15 in 53 and 15% yields, respectively. Refluxing of 9b in 99% formic acid gave 15 in 43% yield. Double cyclization of 7b to 14 and 15 was achieved by refluxing in 99% formic acid in 7 and 47% yields, respectively. In marked contrast, treatment of 9c with formic acid resulted in the formation of the 1, 3-dihydro-4-hydroxy-2-methylthio-2H-indol-2-one 16 and the 3, 5, 6, 7-tetrahydro-1H-indole-2, 4-dione 17 in 47 and 16% yields, respectively.
