Renzo Cabrino

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

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.

On the reactions of alkanedithiols with picryl halides

The reaction of picryl chloride with ethane-1,2-dithiol and base leads to a spiro-σ-adduct via the initially formed 2-picrylthioethanethiol. Similar behaviour has been found with propane-1,3-diol and picryl iodide. In contrast, with propane-1,3-dithiol in place of ethane-1,2-dithiol the initially formed 3-picrylthiopropane-1-thiol collapses via intramolecular displacement of an ortho-nitro-group; no spiro-σ-adduct was detected. With butane-1,4-dithiol or pentane-1,5-dithiol and picryl chloride only polymers were isolated.

General synthesis of tropolone ethers

Reaction of 2-chlorotropone with an excess of an alkoxide in dimethyl sulphoxide gives the gem-dialkoxy adduct (2) which on neutralization affords 2-alkoxytropone, failure only occurring for very bulky alkoxides.

Regiospecific amination of deactivated cycloheptatrienones via hydride replacement

3-Dialkylaminotropones and 3-alkoxytropones can be regiospecifically aminated at C-7 with either primary or secondary amines in benzene, whilst 3-alkyl-aminotropones resist amination.