Abstract
N-Cyano- or N-(p-toluenesulfonyl)-N'-(trimethylsilylmethyl)-S-methylisothioureas (3, 4), readily prepared by reactions of S, S'-dimethyl N-cyano- (1a)b and S, S'-dimethyl N-(p-toluenesulfonyl)- (1b) carbonimidodithioates with trimethylsilylmethylamine (2a), followed by N-alkylation, have been found to provide synthetic equivalents of iminoazomethine ylide. Treatment of these compounds with cesium fluoride in the presence of reactive hetero-dipolarophiles such as carbonyl compounds afforded 1, 3-dipolar cycloadducts, 4, 5-dihydro-2-iminooxazoles and 4, 5-dihydro-2-iminothiazoles, via the 1, 3-elimination of (methylthio)trimethylsilane.S-Methyl-S'-trimethylsilylmethyl N-cyano- (5a) and N-(p-toluene-sulfonyl)- (5b) carbonimidodithioates, also readily prepared from the corresponding 1a and 1b with (mercaptomethyl)trimethylsilane (2b), were used as new reagents for introducing a thioformaldehyde unit at a carbonyl carbon. Reactions of these compounds with aldehydes in the presence of cesium fluoride afforded thiiranes via the 1, 3-dipolar cycloaddition of iminothiocarbonyl ylide to the C=O double bond. Reactions of 5 with dimethyl fumarate and maleate in the presence of cesium fluoride in acetonitrile gave 1, 3-dipolar cycloadducts, dimethyl 2-(N-(p-toluenesulfonyl)imino)tetrahydrothiophene-3, 4-dicarboxylates.
