CYCLOADDITION - ELIMINATION-REACTIONS OF 5-IMINO-1,2,4-THIADIAZOLIDIN-3-ONES AND 5-IMINO-1,2,4-DITHIAZOLIDIN-3-ONES WITH ELECTRON-RICH DOUBLE-BONDS

5-Imino-1,2,4-thiadiazolidin-3-ones 1 react with compounds containing electron-rich double bonds such as enamines and ester enolates to affo rd the 2-iminothiazolidines 3, 4, and 10 in cycloaddition-elimination reactions. The less reactive 5-imino-1,2,4-dithiazolidin-3-ones 2 only give the 2-iminothiazolidines 3 or 4 with enamines; with ester enolat es the 5-alkylidene-1,2,4-dithiazolidines 12 are formed. The reaction products with enamines undergo hydrolysis and elimination to form the corresponding hydroxy compounds 5, 6 or the unsaturated compounds 7, 8 , depending on the size of the fused ring.