ADDITION OF TWISTED 1-THIOACYL-2,2-DIAMINOETHYLENES TO DIMETHYL ACETYLENEDICARBOXYLATE - FORMATION AND RING-OPENING OF THIOPYRAN-4-SPIRO-2'-(1',3'-DIAZACYCLANES)

Reaction of 1,3-dialkyl-2-(4,4-dimethyl-2,6-dithioxocyclohexylidene)imidazolidines and -hexahydropyrimidines (twisted push-pull ethylenes, 3) with methyl iodide followed by treatment with base leads smoothly to S-methyl derivatives, which are betaines with a 1,4-dipole and an electron-rich 1,3-butadiene system (5). These compounds react with DMAD to give dihydrobenzothiopyranspiroimidazolidine and -hexahydropyrimidine derivatives 7 in high yields. The spiro compounds rearrange in acid medium or on chromatography on silica gel to compounds, which we previously incorrectly described as ''folded ethylenes'' A but which are now shown to be 4-(2-aminoethyl)amino-ethyl)amino- or 4-(3-aminopropyl)aminothiopyran derivatives 11. The 4-amino groups of 11 are twisted out of the thiopyran plane by the flanking substituents, and the barrier to rotation through the plane was found by NMR bandshape analysis to be 17.8 kcal/mol for the (2-aminoethyl)amino and 16.9 kcal/mol for the (3-aminopropyl)amino group. A 1:2 adduct of 5 and DMAD which we also previously incorrectly described as a folded ethylene (B), was shown to be an aminomaleic ester derivative 12 formed by addition of the NH group of 11 to DMAD.