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The synthesis of tri-substituted pyrazoles was achieved via direct N-heterocyclization of hydrazines with metal-acetylacetonate and -dibenzylideneacetonate without using any base or additives under microwave irradiation in a single step.

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A transition metal‐free protocol has been developed for the oxidative coupling of primary amines to imines and azobenzenes, thiols to disulfides, and 2‐aminothiophenols to benzothiazoles, offering excellent yields. The advantageous features of the present environmentally benign methodology include the usage of biocompatible and green reaction conditions such as, solvent, room temperature reactions and transition metal‐free approach. Moreover, it offers a broader substrate scope.

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A transition metal-free, one step approach has been developed for the synthesis of pyrazolopyrimidinones using in-situ condensation of benzylamines, benzylalcohol and benzaldehyde with 4-amino-2-methyl-5-propyl-2H-pyrazole-3-carboxylic acid amide promoted by K 2 S 2 O 8 and water at room temperature. Present protocol tolerated various functional groups such as halides (Cl, F, Br), methoxy, ethoxy, hydroxyl, nitro, trifluromethyl, trifluoromethoxy and was also applicable to heterocyclic moieties. Different arylated pyrazolopyrimidinones were prepared in good to excellent yields. In the present reaction, K 2 S 2 O 8 is catalyzing the formation of imine as well helping in the cyclization to the desired product. We also reduced the industrially used synthesis steps for sildenafil analogues and prepared in three steps using present method. Arylquinazolinones were also synthesized in high yields using anthranilamide and benzylamines by this methodology.

Continuing research with our earlier finding of sildenafil based analogs in the search of new inhibitors of PDE5 for erectile dysfunction suggested that there is a scope of modifications at N-methylpiperazine ring with hydrophobic region followed by hydrogen bond donor or acceptor region. However, the leads identified earlier had some limitations like poor pharmacokinetic (PK) profile, low aqueous solubility and poor bioavailability. In this direction, a new series of sildenafil based analogs were designed, synthesized and screened for their PDE5 inhibitory activity. In this series compound 18 was found to have excellent in vitro activity with selectivity towards PDE5 isozyme, also the in vivo activity and pharmacokinetic profile was excellent. The cyp inhibition and CaCO 2 permeability was also excellent for compound 18.

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