From Thioamides and Acetylenedicarboxylic Acid

From Thioamides and Acetylenedicarboxylic Acid. The interaction of o-aminobenzenethioamides and dimethyl acetylenedicarboxylate does not yield the quinazoline-4(l )-thione (164) as might be expected from the behaviour of the corresponding o-aminobenzamides, but produces 2-(o-aminophenyl)-5-methoxycarbonylmethylidene-2-thiazolin-4-one (165) in high yield.  

The structure of the condensation products of thioureas and dimethyl acetylenedicarboxylate had not been assigned with certainty. This problem has now been resolved, in one case, by 2f-ray analysis. Thus the addition of iV-thiocarbamoylpiperidine to the acetylenic reagent, which may theoretically give rise to six isomeric products, yields in fact 5-methoxy-carbonylmethylene-2-piperidino-2-thiazolin-4-one, having the geometrical configuration shown in (166). Confirmation has also been provided that the reaction of thiourea with bromosuccinic, maleic, fumaric, or acetylenedicarboxylic acids yields, in each case, a 2-thiazoIine, e.g. (167).  

The results exclude possible alternative thiazine structures that have been considered from time to time. 

Further Syntheses from Thioamides (Linear and Cyclic). The acid-catalysed cyclization of A -allylthioureas provides a synthetic route to 2-thiazolines. The reaction, performed in 60—90% sulphuric acid, is initiated by protonation, producing the highly resonance-stabilized thiazolinium cations (168), and is completed by hydrolysis to (169). It is an example of 

The condensation of JViV-disubstituted thioureas and iminochlorides of oxalic acid (175) [including bis-sulphonyliminochlorides (175 R = S02ph)] in tetrahydrofuran affords 2-dialkyl(or aryl)aminothiazolidine-2,4-dione bisimides (176). Thiobenzamide generally yields linear adducts, e.g. PhCSNHC( NPh)C( NPh)Cl, but affords 2-thiazolines (177) under suitable conditions.  

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