Some aspects of the chemistry of 1,2,3,-triazoles
In a wide rang1ng reaction dimethyl diazomalonate reacted with pr1mary amines to yield the corresponding ammonium salts of 5-hydroxy-I,2,3-triazoles in high yields. On acidification of these salts the free 5-hydroxy-I,2,3-triazoles were obtained quantitatively. When the 5-hydroxy-I,2,3-triazoles were isolated, they were found to be contaminated with «-diazoamides. These diazoamides arise from Dimroth Rearrangement of the 5-hydroxy-triazoles. This Rearrangement was thoroughly investigated and mechanisms were suggested for the base induced cyclisation of diazoamides ) salts of 5-hydroxy-triazoles, and for the thermally promoted decomposition of 5-hydroxy-triazoles-4)~ - diazoamides. The hydroxy-triazoles were converted to 5-chloro-derivatives, under mild conditions, in good yields, using phosphorus pentachloride. These 5-chloro-triazoles proved to be very inert to a variety of nitrogen nucleophiles. When 5-chloro-4-methoxycarbonyl-I,2,3-triazoles were reacted with ammon1a, ammonolysis of the 4-ester function results. The 5-azido-triazoles resulted from reaction of 5-chloro-derivative with sodium azide in moderate yields. Catalytic hydrogenation of 5-azido-I,2,3-triazole furnished excellent yields of 5-amino-I,2,3-triazoles. Attempted preparation of 8-azapurines from 5-hydroxy- and 5-chlorotriazoles with amidines or amides proved fruitless. 9-p-Methoxybenzyl-8-azapurin-6-one was prepared from formamide and l-p-methoxybenzyl-4-carboxamido-5-amino-l,2,3-triazole in a moderate yield. When the 5-amino function was methylated the pyrimidine ring formation is effected with acidified triethyl orthoformate. 9-p-Nethoxybenzyl-8-azaadenine was prepared by chlorination of 9-p-methoxybenzyl-8-azapurine-6-one followed by reaction with ethanolic ammonia. Attempted formation of the pyrimidine rlng uSlng imidates failed. 5-Diazo-l,2,3-triazoles were prepared and cycloaddition reactions were carried out on these compounds. The 5-diazo-triazoles proved unreactive and only decomposition was observed. 4-Aminomethyl-5-amino-l,2,3-triazoles were obtained by reduction of the 4-carboxamido-triazoles with diborane. A convenient preparation of 9-p-methoxybenzyl-l,6-dihydro-8-azapurine was described. A fully protected 1,6-dihydro-8-azapurine ribonucleoside is prepared using this methodology in a 10% yield. The deprotected form was not isolated. In an effort to synthesise truncated 8-azapurine ribonucleosides, allylic triazoles were prepared. After extensive investigations these triazoles were shown to be of no apparent use in the preparation of the target compound.