Well-Defined Phosphine-Free Manganese(II)-Complex-Catalyzed Synthesis of Quinolines, Pyrroles, and Pyridines

Abstract

Herein, we report a simple, phosphine-free, and inexpensive catalytic system based on a manganese­(II) complex for synthesizing different important N-heterocycles such as quinolines, pyrroles, and pyridines from amino alcohols and ketones. Several control experiments, kinetic studies, and DFT calculations were carried out to support the plausible reaction mechanism. We also detected two potential intermediates in the catalytic cycle using ESI-MS analysis. Based on these studies, a metal–ligand cooperative mechanism was proposed.

Biogenic synthesis of δ‐MnO2 nanoparticles: A sustainable approach for C‐alkylation and quinoline synthesis via acceptorless dehydrogenation and borrowing hydrogen reactions

“…The implementation of the hydrogen autotransfer (HA) or acceptorless dehydrogenative coupling (ADC) strategy for the alkylation of ketones and its subsequent cyclization has emerged as an eco-friendly approach for the construction of C-C or C-N bonds compared with the traditional methods. [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] Therefore, the HA/ADC strategy has earned enormous attention because of (a) the use of alkylating agents such as feedstock alcohol; (b) the one-pot reaction as well as high atom and step economy; (c) substrate pre-activation is not required; and (d) only water and H 2 gas as side-products. The catalytic acceptorless dehydrogenation of an alcohol to form a carbonyl compound, which can easily undergo aldol condensation or imine formation, is one of the key advantages of this strategy.…”

“…Notably, the reaction with a decrease in catalyst loading works with lesser yields. [55][56][57][58][59][60][61][62][63][64][65][66][67][68] After having the optimal condition in hand (Table 2, entry 5, S4), the scope of various acetophenone derivatives (1a-1e) with benzyl alcohol (2a) was examined to achieve the corresponding alkylation derivatives (3a-3e) (Table 3). The acetophenone bearing electron-donating 4-methoxy, 4-methyl, and electron-withdrawing 4-bromo groups smoothly delivers the desired product from 3b to 3d in excellent yield.…”

“…[101][102][103] The plausible mechanism is depicted for the δ-MnO 2 NPs catalyzed alkylation and the cyclization reaction with the help of literature presidents and control experiments (Scheme 5). [55][56][57][58][59][60][61][62][63][64][65][66][67][68][92][93][94][95] The biogenically synthesized δ-MnO 2 NPs facilitate the dehydrogenation of benzyl alcohol via HA strategy to form a benzaldehyde, which subsequently gets coupled with the enolate of acetophenone, leading to the aldol product 3 0 upon elimination of water. Further, hydrogen shuttling by catalyst helps to deliver alkylation product 3 completing the ADC reaction with the elimination of catalyst for the next cycle.…”

Orthometallated Pd(ii) C^N^S pincer complex catalyzed sustainable synthesis of bis(indolyl)methanesviaacceptorless dehydrogenative coupling of alcohols

“…Unlike the aforementioned conventional methodologies, acceptorless dehydrogenative coupling reactions (ADC) do not necessitate the consumption of strong oxidants or sacrificial acceptors, and they do not generate stoichiometric amounts of undesirable by-products. [19][20][21][22][23][24][25][26][27][28] In addition, alcohols have several advantages, including their low cost, low environmental impact, and ease of production from biomass derived from lignocellulose. Utilizing alcohol as a principal feedstock in chemical reactions lessens the reliance on finite carbon fossil fuel resources and lowers carbon dioxide emissions.…”

Sustainable synthesis of azobenzenes, quinolines and quinoxalines via oxidative dehydrogenative couplings catalysed by reusable transition metal oxide–Bi(iii) cooperative catalysts

“…By developing pincer-type transition metal catalysts and their phosphine-free alternatives, these goals can be achieved more or less readily, which has made the production of quinolines and quinoxalines more efficient and sustainable than before. [54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72] However, these ADCs have numerous limitations that are very similar to those of their noble metal-based counterparts. When using these complex systems, the only way to obtain the desired product is to use special ligands, additives and/or stoichiometric amounts of bases, inert atmosphere in most of the cases, and usually in non-green solvents (e.g., toluene).…”