Pd(ii)-catalyzed annulation of terminal alkynes with 2-pyridinyl-substituted p-quinone methides: direct access to indolizines

Abstract

A Pd-catalyzed direct method has been developed to access 1,3-disubstituted indolizines. This reaction proceeds through a regiospecific annulation of terminal alkynes with 2-pyridinyl-substituted p-quinone methides and, in most of the...

Cu(I)-Catalyzed Three-Component Annulation for the Synthesis of 3-Acyl Imidazo[1, 5-a]Pyridines from 2-Pyridinyl-Substituted p-Quinone Methides, Terminal Alkynes, and TsN3 Using O2 as the Oxygen Source

“…According to these control experiments and previous reports, 12 we propose the possible mechanism for the reactions, as shown in Scheme 4. First, phenylacetylene (2a) reacts readily with TsN 3 (3a) to give a ketenimine intermediate A in the presence of CuI and Et 3 N, 13…”

“…10c As one of the important members of p-QM families, 2pyridinyl-substituted p-QMs, which have a potential nucleophilic pyridine group, might be able to be used as unique precursors for the synthesis of 3-acyl-imidazo [1,5-a]pyridines by reacting with other suitable substrates. 12 We will herein disclose a new and unprecedented strategy to access 3-acyl imidazo [1,5-a]pyridines by involving a Cu(I)-catalyzed intermolecular three-component annulation multicomponent reactions (MCRs) from 2-pyridinyl substituted p-QMs, terminal alkynes and sulfonyl azides. (Scheme1e)…”

“…Among them, p -QMs exhibited obvious advantages in diverse annulation reactions to form carbocycles/heterocycles, which provided a facile method for constructing large functionalized cyclic molecular libraries with precisely defined stereochemical features from various simple synthons with high step economy, efficiency, and scalability . As one of the important members of p -QM families, 2-pyridinyl-substituted p -QMs, which have a potential nucleophilic pyridine group, might be able to be used as unique precursors for the synthesis of 3-acyl- imidazo­[1,5- a ]­pyridines by reacting with other suitable substrates . We will herein disclose a new and unprecedented strategy to access 3-acyl imidazo­[1,5- a ]­pyridines by involving a Cu­(I)-catalyzed intermolecular three-component annulation multicomponent reactions (MCRs) from 2-pyridinyl substituted p -QMs, terminal alkynes and sulfonyl azides.…”

Nanoarchitectonics of Non-Noble-Metal-Based Heterogeneous Catalysts for Transfer Hydrogenation Reactions: Detailed Insights on Different Hydrogen Sources

“…But there are some other hydrogen sources which are not much explored, like ammonium formate (HCOONH 4 ), ethylene glycol (C 2 H 6 O 2 ), 2-butanol, etc. Conventionally, water gas (CO/H 2 O) were used for the hydrogenation of nitroarenes; however, because of its toxic nature, it was not recommended and, as a result, HCOONH 4 comes into play, which is a renewable reductant and decomposed thermally to produce ammonia, hydrogen, and carbon dioxide. − Moreover, ethylene glycol is also used a H-source which is an odorless and colorless liquid. It is inexpensive, renewable, and has a hydrogen storage capacity of 6.5 wt %.…”

Cu(II)‐Catalyzed [3+2]‐Annulation of 2‐Pyridinyl‐substituted p‐Quinone Methides with Enaminones: Access to Functionalized Indolizine Derivatives

“…In line with this, very recently, our research group developed a palladium‐catalyzed [3+2]‐annulation of terminal alkynes with 2‐pyridinyl‐substituted p‐ QMs to synthesize 1,3‐disubstituted indolizine derivatives ( d , Scheme 1). [14] In fact, this was the first and only report available on the utilization of 2‐pyridinyl‐substituted p‐ QMs as synthons for fused N ‐heterocycles. Since our primary interest is inclined towards developing new protocols to access various O ‐ and N ‐heterocycles from p ‐QMs, we hypothesized that it could be possible to access indolizine derivatives through [3+2] annulation of 2‐pyridinyl substituted p ‐quinone methides and enaminones ( e , Scheme 1).…”