A route to 6-functionalised 1,3-diaza-azulenes and aminotropones via hydride replacement from cycloheptatrienones

Abstract

4-Methylthiotropone regiospecifically cyclises with toluamidine in benzene, but less readily in dimethyl sulphoxide, to give 6-methylthio-2-p-tolyl-1,3-diaza-azulene. With dimethylamine hydride replacement occurs in dimethyl sulphoxide (but not in benzene) at both C(7) and C(2)(ca. 1 : 1 ratio) to give the corresponding amino(methylthio)tropones which are slowly de(methylsulphenyl)ated in the reaction medium. This reaction is favoured by oxidising agents such as potassium ferricyanide. In contrast, 4-methoxy-, 4-dimethylamino-, and 2-dimethylamino-substituents inhibit reactions by both amidines and amines with the cycloheptatrienone nucleus. Further attempts directed at obtaining 4-functionalized 1,3-diaza-azulenes failed because both 2-ethylthiotropone and 2-dimethylsulphoniotropone tetrafluoroborate cyclise with benzamidine to give the corresponding 1,3-diazaazulene with loss of sulphur.