Thiazolo-- and --sym-triazoles

Thiazolo-[2 c] and -[3,2-h] sym-triazoles (C2Nj-CjNS).—3-(2-Furyl)-5-phenylthiazolo[2,3-c]-sym-triazole (126) is obtainable from the appropriate triazole-5-thiol and phenacyl bromide by Hantzsch s synthesis.Members of the isomeric [3,2-b]-ring system (127) have been obtained by annelating 

Imidazo[2,l b]tliiazoles (C3NS C3N2) — The reaction of 2-mercaptoimida-zoline (128 R = H) with ethyl chloroacetate yields the expected 5,6-dihydro-4H-imidazo[2,l-b]thiazol-3(2H)-one (129 R = H). In the same reaction, 4-methyl-2-mercaptoimidazoline (128 R = Me) affords the substituted thiazolidine-2,4-dione (130 R = Me), presumably by ring-cleavage of the 

Imidaz6[2,l-b]thiazoles (132) are further obtainable in good yield from 2-aminothiazoles (131) by the action of phenylacyl bromide, or from 2-imino-3-(2-propynyl)-A -thiazolines (133) by alkahne cyclization. Thiocyanation of (132) and (134) yields the corresponding 5-thiocyanato-derivatives. The synthesis by established routes of further examples of this ring-system has been recorded.  

Pyrrolo[2,l-b]thiazoles (C3NS-C4N).— Pyrrolo[2,l-b]thiazoles have been thioformylated by a novel application of the Vilsmeier reaction. Treatment of the reactants (135) with phosphoryl chloride in DMF produces the Vilsmeier salts (136), which are convertible into the orange or red pyrrolo[2,l-b]thiazole-5-thioaldehydes (137) by thiohydrolysis, using sodium hydrogen sulphide. The isomeric 7-thioaldehydes (138) are similarly 

Thieno[2,3-d]thiazoles (C3NS-C4S).—2-Aminothieno[2,3-d]thiazoles (139) are accessible from 2-aminothiophen by way of 3-thiocyanato-derivatives, followed by cyclization.  

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