Arene Binuclear Ru(II)-Promoted Sustainable Synthesis of Substituted Pyrazoles from Alcohols via Acceptorless Dehydrogenative Annulation.

ABSTRACT

We report a selective and sustainable synthesis of substituted pyrazoles via an eco-friendly acceptorless dehydrogenative annulation (ADA) of greener alcohols, malononitrile, and various aromatic hydrazides by newly synthesized binuclear Ru(II) p-cymene complexes. A discrete set of binuclear Ru(II) complexes are fabricated and structurally characterized by analytical, spectral, and single-crystal X-ray diffraction methods. Further, the catalytic effectiveness of the complexes is explored for the construction of 5-amino-4-cyano-N-aroylpyrazoles (34 examples) under mild conditions and produces H2O/H2 as the only byproduct. A sequence of polysubstituted pyrazoles has been constructed in 62-95% yield using 1 mol % catalyst loading. Probable intermediates detected in the catalytic reaction have been isolated and confirmed by nuclear magnetic resonance and electrospray ionization mass spectrometry studies. Expediently, a therapeutically significant gout medicine "allopurinol" analogue has been derived successfully from the synthesized 5-amino-4-cyano-N-aroylpyrazoles.