V-Triazolo[4,5-d]pyrimidines (8-azapurines). Part XIV. Synthesis of 6-unsubstituted 8-azapurines from ring N-alkylated 4-amino-1,2,3-tri-azole-5-carbaldehydes

Abstract

4-Amino-3-benzyl-1,2,3-triazole-5-carbaldehyde (6c), on treatment with phosphoryl chloride and dimethyl-formamide, gave 3-benzyl-4-dimethylaminomethyleneamino-1,2,3-triazole-5-carbaldehyde (7), which was cyclised by ammonium acetate to give 9-benzyl-8-azapurine (1b). Likewise, 7-(and 8-)methyl-8-azapurine were obtained from 4-amino-1 -(and 2-)methyl-1,2,3-triazole-5-carbaldehyde, respectively. The foregoing amino-aldehydes, heated with triethyl orthoformate, triethyl orthoacetate, and tetraethyl orthocarbonate, yielded (respectively) 4-ethoxymethyleneamino-, 4-(α-ethoxyethylideneamino)-, and 4-diethoxymethyleneamino-derivatives, which were cyclised by ammonia to give 7-methyl-, 9-benzyl-, 9-benzyl-2-methyl-, 2,7- and 2,8-dimethyl-, 9-benzyl-2-ethoxy-, and 2-ethoxy-8-methyl-8-azapurines.Fission of 9-benzyl-2-ethoxy-8-azapurine gave 9-benzyl-8-azapurin-2-one. 2-Amino-8-methyl(and 2-amino-9-benzyl)-8-azapurine were made from the corresponding 2-ethoxy-derivatives and ammonia. 4-Amino-3-benzyl-1,2,3-triazole-5-carbaldehyde was converted into 4-amino-3-benzyl-5-dimethoxymethyl-1,2,3-triazole (13) and a condensed product (14). The amino-acetal (13) and ethyl chloroformate yielded 3-benzyl-4-ethoxy-carbonylamino-1,2,3-triazole-5-carbaldehyde. An improved synthesis of 4-amino-2-methyl-1,2,3-triazole-5-carbaldehyde is given, I.r. and n.m.r. spectra are recorded and discussed.