An Olefinic 1,2‐Boryl‐Migration Enabled by Radical Addition: Construction ofgem‐Bis(boryl)alkanes

Abstract

As eries of in situ formed alkenyl diboronate complexes from alkenyl Grignard reagents (commercially available or prepared from alkenyl bromides and Mg) with B 2 Pin 2 (bis(pinacolato)diboron) react with diverse alkyl halides by aR up hotocatalyst to give various gem-bis-(boryl)alkanes.A lkyl radicals add efficiently to the alkenyl diboronate complexes,and the adduct radical anions undergo radical-polar crossover,s pecifically,a1,2-boryl-anion shift from boron to the a-carbon sp 2 center.T his transformation shows good functional-group compatibility and can serve as ap owerful synthetic tool for late-stage functionalization in complex compounds.M easurements of the quantum yield reveal that aradical-chain mechanism is operative in whichthe alkenyl diboronates acts as reductive quencher for the excited state of the photocatalyst.

Versatile cobalt-catalyzed regioselective chain-walking double hydroboration of 1,n-dienes to access gem-bis(boryl)alkanes

“…7a). Similarly, the reaction between (E)-but-2-en-1-ylbenzene (17) and HBpin under standard conditions afforded alkylboroante products 15 and 16, albeit with a low regioselectivity (15:16 = 61:39), and both products were resulted from chain-walking hydroboration (Fig. 7b).…”

“…Interestingly, gem-bis(boryl)alkanes can generate two types of carboanions, monoboryl-or gem-bis(boryl)-functionalized carboanions, via deprotonation by LiTMP (lithium tetramethylpiperidide) or alkoxide-induced deborylation 11,12 . Over past decades, series of catalytic reactions have been developed to access these gem-bis(boryl) compounds [13][14][15][16][17] , such as double hydroboration of alkynes [18][19][20] , diborylation of alkenes 21,22 , hydroboration of 1-borylalkene [23][24][25] , or C-H borylation reactions [26][27][28][29] . Nevertheless, a general and practical approach that combines high catalytic activity, easy accessibility and handling of starting materials, and structural diversity of gem-bis(boryl) products is still lacking.…”

Radical‐Induced 1,2‐Migrations of Boron Ate Complexes

“…In additional mechanistic experiments, the authors could further support that the mechanism likely proceeds via an outer‐sphere electron transfer process (see Scheme a). More recently, Shi and co‐workers demonstrated that in situ generated alkenyl diboron ate complexes derived from alkenyl‐Grignard reagents and bis(pinacolato)diboron undergo efficient radical‐induced 1,2‐boron to carbon shifts of a boron group to give various gem ‐bis(boryl)alkanes (Scheme d) . Of note, the quantum yield of this process was determined to be Φ=49.8, clearly showing that the Ru complex mainly acts to initiate an innate radical chain reaction.…”

Wet carbonate-promoted radical arylation of vinyl pinacolboronates with diaryliodonium salts yields substituted olefins

“…Ph 2 I + OTf − 1e was triggered by CO 3 2− to give I, which accelerated radicals 8e and PhI-CO 3 − formed via homo cleavage. The intermediate II formed from vinylboronate 2a and CO 3 2− enabled the addition of radicals 8e to form the C-C bond [45][46][47] , generating the "ate" α-boronate adduct radical species III [48][49][50][51][52] . Species III was capable of occurring SET reaction with radical CO 3 − to give the intermediate moiety IV and intramolecular dehydrocarbonate give the "ate" intermediate VI, which further eliminated to give the desired product 3e.…”