Collaborative Interaction of Carbon–Carbon Unsaturated Bond Groups with Transition-metal Catalysts for C–H Bond Functionalization

Abstract

Alkynes, alkenes, and thiophenes are found to behave as a directing group for CH bond activation by a transition-metal catalyst. This collaborative interaction led to the discovery of not only simple intramolecular cyclizations but also carboncarbon bond formation or annulation reactions with other reactants involving such unsaturated bond-directing groups. This highlight review discusses the recent progress in this sort of novel synthetic tools.

Cobalt(II)-Catalyzed Acyloxylation of C–H Bonds in Aromatic Amides with Carboxylic Acids

“…Transition-metal-catalyzed C–H functionalization has received increasing attention in organic synthesis because of its step- and atom-economy advantages, environmental friendliness, and the fact that prefunctionalized substrates are not needed . The efficiency and scope of C–H functionalization reactions at the ortho-position of arenes has been substantially improved in the past decades.…”

Allyl Monitorization of the Regioselective Pd-Catalyzed Annulation of Alkylnyl Aryl Ethers Leading to Bismethylenechromanes

“…Then, the formation of the carbon−carbon bond to give product P is mediated by the metal with a TS lower in energy than the previous intermediate, which is associated with the dispersion correction effects. 17 Going to the green path, first, the metalmediated carbon−carbon bond-forming insertion occurs, with a kinetic energy cost from VI of only 3.6 kcal/mol. Afterward, a transformation of the terminal alkene moiety to a methylenic group directly bonded to palladium occurs, leading to intermediate VII−2.…”

“…This finding is not unprecedented, because the stabilizing effect of the electron-withdrawing group of η 1 -allyl-Pd complexes has already been reported by Solin and Szabo. 17 As an exception, the bulky tBu group destabilizes TS III−IV enough to make it higher in energy than TS II−III, leading to a higher energy barrier of 39.3 kcal/mol.…”

Nickel-Catalyzed C−H Functionalization Using A Non-directed Strategy

“…In the last few decades, late and noble transition-metal catalysts have been extensively used in C-H bond functionalization because of the straightforward approach in organic synthesis. [35][36][37][38][39][40][41][42] Ni-catalyzed C-C bond formation has recently become a subject of great interest, because of the low cost, ready availability, and the uniqueness of such catalysis. [43][44][45][46] Moreover, nickel is capable of existing in various oxidation states, such as Ni(0)ÀNi(IV), which provides different redox pathways such as Ni(0)/Ni(II), Ni(I)/Ni(III), 47 and Ni(0)/Ni(II)/Ni(III)/Ni(I) 48,49 during reactions.…”