Arene Binuclear Ru(II)-Promoted Sustainable Synthesis of Substituted Pyrazoles from Alcohols via Acceptorless Dehydrogenative Annulation
Tamilthendral Veerappan, Rengan Ramesh
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 H 2 O/H 2 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.