Sulphonated graphene oxide catalyzed continuous flow synthesis of pyrazolo pyrimidinones, sildenafil and other PDE-5 inhibitors.

Sulphonated graphene oxide was used for cascade condensation and cyclization reactions towards accessing substituted pyrazolo pyrimidinones. Further, sulphonation and amination reactions were integrated through continuous flow chemistry to access PDE-5 inhibitors. Herein, we report a simple continuous synthetic platform that reduce tedious manual operations and accelerate the synthesis of several potent inhibitors of phosphodiesterase type-5. The developed platform enabled us to perform one-flow multi-step, multi-operational process to synthesize the PDE-5 inhibitors such as sildenafil and its analogues in 32.3 min of the reaction time, with minimal human intervention and single solvent.