Formation of C–B, C–C, and C–X Bonds from Nonstabilized Aryl Radicals Generated from Diaryl Boryl Radicals

Abstract

With the development of organoboron chemistry, boron-centered radicals have become increasingly attractive. However, their synthetic applications remain limited in that they have been used only as substrates for addition reactions or as initiators for catalytic reactions. We have achieved a new reaction pathway in which tetraarylborate salts are used as precursors for aryl radicals via boron radicals, by introducing a simple activation reagent. In addition, we carried out a diverse array of transformations involving these aryl radical precursors, which allowed the construction of new C−B, C−C, and C−X bonds in the presence of visible light.

Hydroalkylation of styrenes enabled by boryl radical mediated halogen atom transfer

“…Tetraphenylborates have historically been used in the generation of biphenyls through electrochemical, [31][32][33][34] thermal 35 or photoredox methodologies 36 and in the formation of aryl radicals 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.…”

“…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.…”