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.
Herein, we demonstrated Mn-catalyzed selective C-3 functionalization of indoles with alcohols. The developed catalyst can also furnish bis(indolyl)methanes from the same set of substrates under slightly modified reaction conditions. Mechanistic studies reveal that the C-3 functionalization of indoles is going via a borrowing hydrogen pathway. To highlight the practical utility, a diverse range of substrates including nine structurally important drug molecules are synthesized. Furthermore, we also introduced a one-pot cascade strategy for synthesizing C-3 functionalized indoles directly from 2-aminophenyl ethanol and alcohol.
The synthesis of N-heterocycles has been considered an emerging topic of chemical research due to its widespread usage in medicinal chemistry, materials science, and natural product synthesis.
Development in the area of acceptorless dehydrogenation (AD) and borrowing hydrogen (BH) catalysis emerge as one of the potential tools for various CÀ C and C-heteroatom bond forming reactions. Alcohols, which are important lignocellulosic biomass products, act as pivotal electrophilic coupling partners in such processes and interestingly only H 2 or H 2 O is eliminated as a byproduct. Initially, the area was developed by the use of noble metal catalysts. Recently, base metals such as Mn, Fe, Co, and Ni proved to be environmentally benign and inexpensive alter-natives for the noble metals in the application of AD and BH methods. This transition metal catalyzed AD and BH approaches also allow access toward a plethora of structurally important heterocyclic molecules via environmentally benign and atom economical strategy. Herein, we summarize the current and rising expansion of base metal catalyzed heterocycles synthesis through acceptorless dehydrogenation and borrowing hydrogenation strategy.
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