Fused Dihydropyrimidines by a Tandem Aza-Wittig-Heterocumulene-Mediated Annulation Reaction: Synthesis of 4,5-Dihydropyrazolo[3,4-d]pyrimidine Derivatives
17 September 2002 (online)
4-Aminomethyl-3-methyl-1-phenyl-5-[(triphenylphosphoranylidene)amino] -1H-pyrazoles 2 (iminophosphoranes), prepared from 4-aminomethylene-3-methyl-1-phenyl-5-[(triphenylphosphoranylidene)amino] -1H-pyrazoles 1, react with aliphatic and aromatic isocyanates in refluxing toluene to give the corresponding 5-substituted 6-alkyl(aryl)amino-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazolo[3, 4-d]pyrimidines 4. Iminophosphoranes 2c and 2d also react with carbon dioxide and carbon disulfide to give 6-oxo- and 6-thioxo-4,5,6,7-tetrahydropyrazolo[3,4-d]pyrimidines 5 and 6 respectively. 4-(N-4-Methylphenyl)aminomethyl-3-methyl-1-phenyl -5-[(triphenylphosphoranylidene)amino]-1H-pyrazole (2d) reacts with acyl chlorides to give 4-[N-acyl(N-4-methylphenyl)amino]methyl-3-methyl -1-phenyl-5-[(triphenylphosphoranylidene)amino]-1H-pyrazoles 7, which by thermal treatment proved resistant to cyclization to give fused pyrimidines.