Thermal reactivity of tricyclic 4,5-diacyltriazolines resulting from addition of aryl azides to 1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone

Abstract

Reaction of 4-methoxyphenyl azide 1a with 1,4-naphthoquinone 10 at 15–100 °C in benzene, dimethyl sulphoxide, or nitromethane leads mainly to the ring-contracted enamine 18a, the ring-expanded 2-benzazepine-1,5-dione 20a, and the aziridine 16a, the decomposition products of an intermediate triazoline 12a, to an extent largely independent of the solvent polarity and the temperature employed. However, the triazole 15a appears to be the main decomposition product of the triazoline 12a produced in hexamethylphosphoric triamide.

A comparable chemical trend is observed with thermal additions of 4-nitrophenyl azide 1b to the quinone 10. Cycloaddition of the azide 1a to 2-methyl-1,4-naphthoquinone 11 leads regioselectively to the formation of the triazoline adduct 13a, which undergoes preferential isomerization to an isolable diazo dione 23a. On the other hand the azide 1b leads to a mixture of the regioisomeric triazolines 13b and 14b. The triazoline 13b, analogously to 13a, rearranges to the ring-opened diazo dione 23b, whereas the triazoline 14b is converted into a mixture of the ring-contracted and ring-expanded products 24b and 21b. The possible reaction mechanisms involved in the decomposition of the triazolines 12a and 12b, 13a and 13b and 14b are discussed.