Forging C–C Bonds through Intramolecular Oxidative Coupling of Organoborates – An Overview

Abstract

C-C bond formation has challenged the community of synthetic organic chemists for a few decades. Organoboron derivatives represent a mild and functional group tolerant class of reagents that can be handled without the need for inert conditions, being therefore adequate scaffolds for further studies towards the development of efficient methods that would increase the sustainability of current processes for coupling reactions. This short review summarizes the different approaches that have been developed to undergo C-C bond formation through intramolecular rearrangements of organoborate species.

Hydroalkylation of styrenes enabled by boryl radical mediated halogen atom transfer

“…Differently functionalized styrenes were efficiently alkylated. Despite the lower yield for styrene (28), which afforded the desired product in 37% yield, methyl (29), phenyl (35), acetoxy (38), -F (30-32), cyano (37), methylthio (39) and -BPin (43) substituents were tolerated. 2-Vinylnaphthalene (34) was functionalized as well.…”

“…37 More recently, Lan, Xia and co-workers employed NaBPh4 as a source of diphenylboryl radical rather than well documented biaryl synthesis to accomplish C-O bond homolytic cleavage. 38,39 Aware of the central role of the solvent (dimethylformamide, DMF) in stabilizing the highly reactive diphenyl boryl radical, we wondered if it could be possible to explore the XAT ability of this reactive intermediate.…”

The Impact of Boron Hybridisation on Photocatalytic Processes

“…The merger of organoboron and photochemistry has a rich history in synthetic chemistry, with the direct excitation of tetraphenylboronate [29] by Williams and co-workers in 1967 serving as a blueprint for future catalytic strategies involving boronates. [30] Building on these seminal contributions, in 2012, Akita and co-workers demonstrated the synthetic potential of potassium trifluoroborates and triolborates as radical precursors in photoredox catalysis (Scheme 1). [31] Gathered knowledge on redox potentials by cyclic voltammetry enabled strategic reaction design, employing [Ir(dF-(CF 3 )ppy) 2 (bpy)](PF 6 ) as a suitable catalyst under blue light irradiation to reductively quench the boronates to form alkyl and aryl radicals.…”

Hydroalkylation of styrenes enabled by boryl radical mediated halogen atom transfer

“…Differently functionalized styrenes were efficiently alkylated. Despite the lower yield for styrene (28), which afforded the desired product in 37% yield, methyl (29), phenyl (35), acetoxy (38), -F (30-32), cyano (37), methylthio (39) and -BPin (43) substituents were tolerated. 2-Vinylnaphthalene (34) was functionalized as well.…”

“…37 More recently, Lan, Xia and co-workers employed BPh 4 Na as a source of diphenylboryl radicals rather than the well-documented biaryl synthesis to accomplish C–O bond homolytic cleavage. 38,39 Aware of the central role of the solvent ( N , N -dimethylformamide, DMF) in stabilizing the highly reactive diphenyl boryl radical, we wondered if it could be possible to explore the XAT ability of this intermediate.…”