Reaction with thieno isothiazole

Thieno[2,3-c]isothiazole-3-carboxylic acid was the compound obtained by the reaction of ethyl 3-cyano-5,5-diethoxy-2-oxopentanoate with phosphorus pentachloride in refluxing toluene, previously assumed (55JA4069) to yield thieno[3,4-c ]isothiazole-4-carboxylic acid. The proposed mechanism involves the cyclization of the intermediate 3-cyano-2,5-dithioxopentanoate as shown in Scheme 20. The parent heterocycle, which is a weak base and fails to give quaternary salts with alkyl halides, was obtained by decarboxylation of the acid and also by independent synthesis (82AJC385). 

Thieno[2,3-c]isothiazoles. - The reaction of (78) with Na in liquid NH3 and then H2O gives 5-methoxythieno[2,3-c] isothiazole (79). ... 

Thieno[2,3-e]isothiazoles. - Reaction of ethyl 3-cyano-5,5-di-ethoxy-2-oxopentanoate with P2S5 in refluxing toluene gives a monoacid, C NO, in 24 yield. The N.M.R. spectrum and unambiguous synthesis showed thi3 to be thieno[2,3-cJisothia-zole-3-carboxylic acid (44) and not the isomeric thieno[3,4-d]-isothiazole (45) as previously suggested. Cyclisation to... 

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