Synthesis of Thiophens by Ring-closure Reactions

Syntheses of Thiophens by Ring-closure Reactions.—The base-catalysed reaction between 3-amino-substituted dithioacrylate esters or amides (1), which are easily available from trithione, and a-halogenocarbonyl compounds yields 2,5-disubstituted thiophens (2). The same is true for 

The Gewald synthesis of 2-aminothiophen-3-carboxylic acid derivatives has been extended to cyanoacetic acid hydrazides. In the base-catalysed reaction with cyclohexanone and sulphur, the hydrazides yielded the thienopyrimidone derivative (24), which could be hydrolysed to the 2-aminothiophen-3-carboxylic acid hydrazide (24a). A series of substituted 2-aminothiophen-3-carboxylic esters have been prepared by a 

The reaction between esters of arylpropiolic acids and esters of thio-glycollic acids, using sodium methoxide in benzene as basic catalyst, leads to a mixture of the hydroxythiophencarboxylic acid esters (26) and (26a), in contrast to what had been reported earlier. Only (26), however, is 

Tilak and co-workers have continued their investigations on the synthesis of 2-ethoxycarbonyl-3-hydroxythiophanes, through the base-catalysed condensation of methyl vinyl ketone, chalcones, ethyl 2-benzoyl-acrylate, and Mannich bases with ethyl thioglycollate. Dehydration of the thiophanes with polyphosphoric add followed by dehydrogenation using chloranil or diphenyl disulphide affords thiophens. 

A new synthesis of 2-aminothiophen has been found in the cyclization of cw-y-benzylthiocrotononitrile with anhydrous hydrogen chloride in a 

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