The synthesis of some 4H-pyrimido[2,1-b]benzothiazol-4-ones

A series of 8-substituted and 7,8-disubstituted-4-oxo-3-(4H-pyrimido2,1-b]benzothiazole)carboxylic acids and esters including a 9-aza analog were synthesized from substituted 2-aminobenzothiazoles and diethyl ethoxymethylenemalonate. The 9-aza analog, ethyl 8-methoxy-4-oxo-3-(4H-pyrido3′,2′:4,5]thiazolo3,2-a]pyrimidine)carboxylate ( 56 ), represents the first preparation of this new heterocyclic ring. These compounds were examined for antiparasitic activity, however, no significant activity was detected.