Synthesis and Mechanistic Investigation of Bipyrazolo[1,5-a]pyridines via Palladium-Catalyzed Cross-Dehydrogenative Coupling of Pyrazolo[1,5-a]pyridines

Abstract

The synthesis of a range of 3,3′-bipyrazolo­[1,5-a]­pyridine derivatives via direct cross-dehydrogenative coupling of pyrazolo­[1,5-a]­pyridine precursors is herein presented. This simple and efficient methodology involving palladium­(II)-catalyzed C–H bond activation showed good functional group tolerance and product yield (up to 94%). Through the mechanistic insights gained from both kinetic isotope effect experimental studies and density functional theory calculations, a plausible reaction mechanism was outlined. Furthermore, subsequent derivatizations of the resulting 7,7′-diaryl-3,3′-bipyrazolo­[1,5-a]­pyridines, executed by performing palladium-mediated ortho C–H bond activation followed by hypervalent iodine-induced chlorination, rendered this series of compounds more extended π-conjugation and twisted conformations. Our study on these bipyrazolo­[1,5-a]­pyridine-based luminogens provides new opportunities for tailor-made organic luminescent materials.

Palladium-Mediated C(sp3)–H Bond Activation of N-Methyl-N-(pyridin-2-yl)benzamide: Direct Arylation/Alkylation and Mechanistic Investigation

“…In transition-metal-mediated C–H bond activation, palladium is a common catalyst that generates robust palladacycle intermediates and introduces high functional group tolerance in the cross-coupling reactions . The cyclopalladation of C–H bonds with a directing auxiliary usually affords dinuclear palladacycles with five- and six-membered rings as the primary intermediates , in the C–H bond activation step. Although four-, seven-, and eight-membered metallacycles , are also found, they are usually less stable as a result of the high ring strain.…”

An eco‐efficient new path of mortar pestle grinding approach for the construction of methanol and ethylthio substituted pyridines with in silico studies

“…The use of multiple reactants in a single step to produce heterocyclic compounds has attracted interest because, it avoids a number of steps and produces more significant results by utilizing a variety of heterogeneous and homogeneous catalysts [12][13][14][15][16][17]. The main drawbacks of heterogeneous catalyst in the organic reactions include, expensive, difficulties in product separation, and recollecting the catalyst for extended periods of time.…”