A novel type of ring closure of amino-substituted thiocarbonyl ylides

The reaction of 4,4-dimethyl-1,3-thiazole-5(4H)-thiones 7a-c with dimethyl 2-diazo-3-(phenylamino)butanoate (2), prepared from dimethyl fumarate and p henyl azide, in toluene at 80 degrees C yielded mixtures of dimethyl 2-(4,5 -dihydro-4,4-dimethyl-1,3-thiazol-5-ylidene)-3-(N-phenylomino)butanedioates of type 11 and four diastereoisomeric 4,4-dimethyl-9-phenyl-1,6-dithia-3,9 -diazaspiro[4.4]non-2-ene-7,8-dicarboxylates of type 12. The formation of t he products of type 12 is rationalized by a novel cyclization of intermedia te thiocarbonyl ylides 9. The structures of cis-12a, cis-12c, and trans-12c were established by X-ray crystallography.