Visible Light Induced Aerobic Coupling of Arylboronic Acids Promoted by Hydrazone

Abstract

A visible-light-induced oxidative coupling of arylboronic acids has been developed for the synthesis of biaryls. The reaction that employs polydentate hydrazones as the bifunctional catalyst works smoothly under room temperature. It is compatible with a wide range of functional group. The study of UV-Vis spectrum indicated that hydrazone and its complex with CuI show major absorptions upon visible-light, which secures the dual role of hydrazone as both ligand and photocatalyst in this reaction. Hence, the reaction is proposed to involve stepwise transmetallations, photo-induced oxidations, and reductive elimination.

Photoactive Copper Complexes: Properties and Applications

“…Transmetallation between the two aforementioned copper species would lead to a copper­(III)–acetylide complex that would undergo reductive elimination, affording the desired product 164 and restoring the catalytic copper­(I) species (Scheme ). As a note, an in situ generated photoactive copper complex resulting from the coordination of polydentate hydrazones to copper­(I) iodide has been shown to promote the visible light-induced, copper-catalyzed aerobic coupling of arylboronic acids …”

Alkylation/Ipso-cyclization of Active Alkynes Leading to 3-Alkylated Aza- and Oxa-spiro[4,5]-trienones

“…Green development has always been an eternal topic in the field of chemistry. − The radical reactions, a class of new and developing reactions, have received extensive attention of chemists because of their mild conditions, rapid reactions, and diverse reaction forms. , Combining the requirements of green development and our interest in radical reactions, we develop a transition-metal-free alkylation/ipso-cyclization of activated alkynes with 4-alkyl-1,4-dihydropyridines for the preparation of 3-alkylated aza - and oxa -spiro­[4,5]-trienones, in which H 2 O provides an oxygen atom for the construction of the newly generated carbonyl group (Scheme ).…”

Polydentate hydrazones as multitasking catalysts in visible-light-induced coupling reactions of amines

“…Based on the above experimental observations and our previous study on Cu/hydrazone catalysis, 21 a plausible reaction mechanism is proposed, as shown in Scheme 1. For the cross-coupling between anilines and arylboronic acids, complex 5 is generated by the reaction of CuCl 2 and hydrazone L 1 in the presence of a base.…”

“…As a continuation of our interest in hydrazine/hydrazone chemistry, we discovered that polydentate hydrazone together with Cu could promote visible-light-induced oxidative coupling of arylboronic acids. 21 Hydrazone/Cu complexes were proposed as active photochemical intermediates, which is supported by UV/Vis analysis. This methodology worked for a wide range of arylboronic acids, leading to the formation of various biaryl compounds (Fig.…”

“…Both L 2 and L 3 are inferior to L 1 , probably due to their poor coordination with copper and shorter absorption wavelength (entries 5 and 6). 21 Replacing DBU with potassium carbonate or DABCO led to trace product (entries 7 and 8). DIPEA could work for the reaction, however, with a much lower yield (entry 9).…”