Herein the first sustainable synthesis of quinoxalines, pyrazines and benzothiazoles catalysed by a phosphine free Mn(i) complex via acceptorless dehydrogenative coupling (ADC) is reported. This method is also applied successfully to synthesize quinolines via the dehydrogenation (removal of H2) and condensation (removal of H2O) reaction between 2-aminobenzyl alcohols and secondary alcohols.
Herein, we present a selective synthesis of 2-substituted and 1,2-disubstituted benzimidazoles by acceptorless dehydrogenative coupling of aromatic diamine with primary alcohols. The reaction is catalyzed by a phosphine-free tridentate NNS ligand-derived manganese(I) complex.
The application of nontoxic, earth-abundant transition metals in place of costly noble metals is a paramount goal in catalysis and is especially interesting if the air-and moisture-stable ligand scaffold is used. Herein, we report the synthesis of amines/imines directly from alcohol and amines via hydrogen autotransfer or acceptorless dehydrogenation catalyzed by welldefined phosphine-free Mn complexes. Both imines and amines can be obtained from the same set of alcohols and amines using the same catalyst, only by tuning the reaction conditions. The amount and nature of the base are found to be a highly important aspect for the observed selectivity. Both the primary and secondary amines have been employed as substrates for the Nalkylation reaction. As a highlight, we showed the chemoselective synthesis of resveratrol derivatives. Furthermore, the Mncatalyzed dehydrogenative synthesis of structurally important 2,3-dihydro-1H-perimidines has also been demonstrated. Density functional theory calculations were also carried out to model the reaction path and to calculate the reaction profile.
A sustainable synthesis of quinazoline and 2aminoquinoline via acceptorless dehydrogenative annulation is presented. The reaction is catalyzed by earth-abundant welldefined manganese complexes bearing NNS ligands. Furthermore, a one-pot synthetic strategy for the synthesis of 2-alkylaminoquinolines through sequential dehydrogenative annulation and Nalkylation reaction has also been demonstrated.
Visible‐light‐induced reactions have allowed researchers to attain unorthodox bond formation and elusive chemical processes under mild and inherently safe reaction conditions. However, these methods have relied heavily on Ru‐ and Ir‐based complexes or metal‐free chromophores. While the heavy transition metal complexes are limited by their high cost, toxicity, and adverse environmental effects. Metal‐free photo‐redox catalysts are restricted due to their poorer photo‐stability. In order to overcome these shortcomings, extensive research aimed towards utilizing 3d‐transition metals has come to the forefront. Manganese, in this regard, holds great promise as a versatile and economically sustainable 3d‐transition metal catalyst. Hence, it is not surprising that recent years have witnessed several advances in visible‐light‐mediated manganese catalysis in areas of organic, polymer, and materials chemistry. Manganese‐based heterogeneous systems have also been utilized to effect dimerization and oxygenation reactions showcasing the versatility of manganese. Moreover, manganese has enabled late‐stage functionalization of valuable medicinal compounds and natural products, which are all important from the viewpoint of medicinal and pharmaceutical chemistry. In the present review, comprehensive discussions on the advances, significance, approaches, and mechanistic aspects have been added for each photochemical reaction process. Further, the reaction scope, limitations, and future prospects of visible‐light‐induced manganese catalysis have also been reviewed.
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