Rearrangement of Derivatives of 1,3-Dithian-5-amineinto Bicyclic 2-Thiazolidines. Crystal Structures of cis- and trans-1-(2-Aryl-1,3-dithain-5-yl)-2-thioureas and cis- and trans-5-Aryl-3-imino-7,7a-dihydro-1H,3H,5H-thiazolo[3,4-c]thiazoles

TLDR: In this paper, a rearrangement of 5-aryl-3-imino-7,7a-dihydro-1H, 3H, 5H-thiazolo[3,4-c]-thiazol-3,1.

Abstract: Under conditions normally applied to transform thioureas into the corresponding carbodiimides, cis- and trans-1-(2-aryl-1,3-dithian-5-yl)-2-thioureas 7 and 8 undergo a rearrangement to 5-aryl-3-imino-7,7a-dihydro-1H, 3H, 5H-thiazolo[3,4-c]thiazoles 9/10 with cis- and trans-fused rings, respectively. The structures of these novel heterocycles were established by X-ray analysis of compounds 9a, 9d, and 10d. The cis-fused compounds 9 are the thermodynamically more stable ones. The stereochemical outcome of the rearrangement depends on the carbenium ion stabilizing capability of the aryl moiety and on the reagent system applied. With Ar = Ph, p-Cl-Ph, p-O2N-Ph, the reaction can be directed to deliver mainly either the cis-thiazolothiazoles 9 or the trans-thiazolothiazoles 10. With Ar = 5-methyl-4-imidazolyl or p-Me2N-Ph, formation of the cis-thiazolothiazoles (9a and 9b, resp.) is strongly favored independently of the reaction conditions, In contrast to it 2-aryl analogs, (1,3-dithian-5-yl)-2-thiourea 7g can be transformed into the carbodiimide 11. Under rigorous conditions, 11 also undergoes rearrangement to the corresponding thiazolothiazole 9g. Mechanisms explaining the above findings are discussed. Reaction of trans-2-phenyl-1,3-dithian-5-amine 6d with phosgene or trichloromethyl chloroformate gives the 5-phenyl-7,7a-dihydro-1H,3H,5H-thiazolo[3,4-c]-thiazol-3-ones 12 and 13, whereas the amine 5g lacking an aryl substitutent forms the sable isocyanate 14. Compound 14 is transformed into the corresponding thiazolothiazolone 15 by refluxing in diglyme. Syntheses are described for the 1,3-dithian-5-amines 5/6 and the thioureas 7/8 derived therefrom. The relative configuration of 7d and 8d was determined by X-ray analysis. NMR data then allowed to assign the configurations of all compounds of types 7 and 8.