A modified, economical and efficient synthesis of variably substituted pyrazolo[4,3-d]pyrimidin-7-ones

Abstract

1-Methyl-3-propyl-1H-pyrazole-5-carboxylic acid (3) was exclusively brominated at the 4-position by bromine in the dark. Brominated product 8 was then converted into 1-methyl-3-propyl-1H-pyrazole-5-carboxamide 9 by successive treatment with thionyl chloride and ammonium hydroxide. Carboxamide 9 was treated with various aroyl amides under microwave (MW) irradiation to afford 4-aroylamino-1-methyl-3-propyl-1H-pyrazole-5-carboxamides 10-22 and 5-aryl-1-methyl-3-propyl-1,6-dihydro-1H-pyrazolo [4,3-d]pyrimidin-7-ones 23-35. The 1H-pyrazole-5-carboxamides 10-22 were also converted to pyrimidinones 23-35 either by conventional heating or by MW irradiation. However, MW irradiation method gives excellent yields in very short time.

An Alternative Approach to Synthesize Sildenafil via Improved Copper-Catalyzed Cyclization

“…. 30 The title compound (26.73 g, 91% yield as a brown solid) was obtained from 5 (20 g, 119 mmol) using N-bromosuccinimide (23.15 g, 131.0 mmol) by the same method that was used for the preparation of 16a: mp 158−161 °C; 1 H NMR (500 MHz, DMSOd 6 ) δ 13.78 (s, 1H), 4.01 (s, 3H), 2.63−2.36 (m, 2H), 1.59 (h, J = 7.4 Hz, 2H), 0.90 (t, J = 7.4 Hz, 3H); 13…”