Simple, straightforward, and atom economic methods for the synthesis of quinolines, 2-aminoquinolines, and quinazolines via biomimetic dehydrogenative condensation/coupling reactions, catalyzed by well-defined inexpensive and easy to prepare singlet diradical Ni(II)-catalysts featuring two antiferromagnetically coupled singlet diradical diamine type ligands are described. Various polysubstituted quinolines, 2-aminoquinolines, and quinazolines were synthesized in moderate to good yields from different low-cost and readily accessible starting materials. Several control experiments were carried out to get insight into the reaction mechanism which shows that the nickel and the coordinated diamine ligands participate in a synergistic way during the dehydrogenation of alcohols.

A simple and efficient approach of C–S cross-coupling of a wide variety of (hetero)­aryl thiols and (hetero)­aryl halides under mild conditions, mostly at room temperature, catalyzed by well-defined singlet diradical Ni­(II) catalysts bearing redox noninnocent ligands is reported. Taking advantage of ligand centered redox events, the high-energetic Ni(0)/Ni­(II) or Ni­(I)/Ni­(III) redox steps were avoided in the catalytic cycle. The cooperative participation of both nickel and the coordinated ligands during oxidative addition/reductive elimination steps allowed us to perform the catalytic reactions under mild conditions.

A general, efficient and environmentally benign, one-step synthesis of substituted quinoline derivatives was achieved by acceptorless dehydrogenative coupling of o-aminobenzylalcohols with ketones and secondary alcohols catalyzed by a cheap, earth abundant and easy to prepare nickel catalyst [Ni(MeTAA)], featuring a tetraaza macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)). A wide variety of substituted quinolines were synthesized in high yields starting from readily available o-aminobenzylalcohols and ketones or secondary alcohols. A few controlled reactions were carried out to establish the acceptorless dehydrogenative nature of the reactions.

A simple metal–ligand cooperative approach for the dehydrogenative functionalization of alcohols to various substituted quinolines and quinazolin-4­(3H)-ones under relatively mild reaction conditions (≤90 °C) is reported. Simple and easy-to-prepare air-stable Cu­(II) complexes featuring redox-active azo-aromatic scaffolds, 2-arylazo-(1,10-phenanthroline) (L 1,2 ), are used as catalyst. A wide variety of substituted quinolines and quinazolin-4­(3H)-ones were synthesized in moderate to good isolated yields via dehydrogenative coupling reactions of various inexpensive and easily available starting materials under aerobic conditions. A few control experiments and deuterium labeling studies were carried out to understand the mechanism of the dehydrogenative coupling reactions, which indicate that both copper and the coordinated azo-aromatic ligand participate in a cooperative manner during the catalytic cycle.