Borrowing Hydrogen and Acceptorless Dehydrogenative Coupling in the Multicomponent Synthesis of N‐Heterocycles: A Comparison between Base and Noble Metal Catalysis

Abstract

In memory of Klaus HafnerAcceptorless dehydrogenative coupling reactions (ADC) and hydrogen transfer strategies (HT) provide a powerful tool in the multicomponent formation of N-heterocycles. A broad variety of complex products can be obtained starting from simple, cheap and commercially available reagents. The protocols are highly atom-efficient, as water, dihydrogen, or in some cases hydrogen peroxide, are the only by-products. Moreover, neither further reducing or oxidizing agents, nor external hydrogen are in general required. Especially base metal-catalyzed strategies become ever more important. Therefore, in recent years, various different manganese, iron, cobalt, nickel and copper catalysts have been developed. This Minireview highlights the progress that has been made by using abundant metal complexes to promote multicomponent cyclizations for the formation of Nheterocycles and compares their performance with available noble metal catalyst systems.

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

“…The development of sustainable catalytic systems for alcohol dehydrogenation and related coupling reactions using earth-abundant transition metals is exciting and highly desirable. − In the past decade, significant progress has been made on 3d transition-metal (Fe, Co, Mn, Ni, etc. )-catalyzed alcohol dehydrogenation and associated reactions because of its higher abundance, lower toxicity, and lesser cost of these metals.…”

Ruthenium pincer complex catalyzed efficient synthesis of quinoline, 2-styrylquinoline and quinazoline derivatives via acceptorless dehydrogenative coupling reactions

“…17,24 Then, 2-aminobenzaldehyde undergoes cyclocondensation with acetophenone to form the quinoline. 14 d , e Likewise, the base promoted cyclocondensation of 2-aminobenzaldehyde with benzonitrile produces the desired quinazoline 7 b , c ,14 b , c and condensation of 2-methylquinoline with benzaldehyde leads to 2-styrylquinoline. 12 c…”

“…6 The process does not rely on any external oxidant source, and by-products are only molecular H 2 and H 2 O, making it green, atom economical, and environmentally benign. Using this dehydrogenative annulation strategy, a variety of pyridine, quinoline, and quinazoline derivatives 7 have been synthesized, catalysed by iridium, 8 ruthenium, 9,10 rhenium, 11 manganese, 12 cobalt, 13 nickel 6 h ,14 and copper 15 complexes. Among transition metal catalysts, ruthenium complexes have been the most efficient to date due to their tunable oxidation states and high catalytic efficacy (Scheme 1).…”

Recent advances in C/N-alkylation with alcohols through hydride transfer strategies

“…The emerging asymmetric versions of BH and ADC catalysis have provided synthetic chemists with reliable procedures to construct C-N and C-C bond stereoselectively, starting with achiral rudimentary alcohols. 4 Established pioneers of hydrogen shuttle catalysis have covered these methodologies to some extent in previous reviews focusing on relevant subtopics such as synthesizing heterocycles 5,6 and designing ligands. 7,8 Additionally, previous reviews have been published introducing the background and perspective of each individual metal separately: Co by Kundu 9 and Young, 10 Mn (Mukherjee), 11 Ru and Ir (Rit), 12 and Fe (Anilkumar), 13 to name but a few.…”