The Behavior of (cyclic‐alkylidene)hydrazinecarbothioamides in Cyclization with Dimethyl acetylenedicarboxylate

A series of (Z)-methyl 2(Z)-3-substituted-2-(cycloalkylidenehydrazono)-4-oxothiazolidin-5-ylidene)-acetate derivatives were synthesized via condensation alkylidene-N-substituted hydrazinecarbothioamides with dimethyl acetylenedicarboxylate. The synthesized compounds were characterized by using different spectroscopic methods and confirmed by single crystal X-ray analysis. The behavior of (cyclic-alkylidene) hydrazinecarbothioamides in cyclization was presented. The mechanism of transformation of (Z)-methyl 2-((Z)-3-(cyclopentylideneamino)-4-oxo-2-(phenylimino)thiazolidin-5-ylidene)acetate (14) into the more stable (Z)-Methyl 2-[(Z)-2-(cyclopentylidenehydrazono)-4-oxo-3-phenylthiazolidin-5-ylidene]acetate (5a) was discussed and confirmed.