Direct and Base-Catalyzed Diboration of Alkynes Using the Unsymmetrical Diborane(4), pinB-BMes₂

Abstract

In the absence of transition metal catalysts, the unsymmetrical diborane(4), pinB-BMes2, reacted with alkynes to afford diborylalkenes. The isomer ratio of the products could be controlled via temperature, solvent, and additive(s). A reaction mechanism was proposed on the basis of two isolated intermediates, and this reaction could furthermore be applied to synthesize a luminescent molecule.

Selective Boryl‐Anion Migration in a Vinyl sp2−sp3 Diborane Induced by Soft Borane Lewis Acids

“…Thes ubsequent addition of BPh 3 to [7] À resulted in suppression of 1,2-boryl migration, with [8] À detected only in trace amounts (Scheme 6). Thes ubsequent addition of BPh 3 to [7] À resulted in suppression of 1,2-boryl migration, with [8] À detected only in trace amounts (Scheme 6).…”

“…The coordination of aL ewis base (LB) to diborane (4) compounds,such as B 2 Pin 2 (1), generates an sp 2 Àsp 3 diborane in which the boron-boron bond is polarised, [1] which imparts nucleophilic character to the sp 2 boron atom, thereby enabling the mild generation of af unctional equivalent of {BPin} À . [1,2] This strategy has become ap owerful transitionmetal-free method to borylate organic substrates and generate desirable organoboronate esters.A lkoxides or Nheterocyclic carbenes (NHCs) are the typical LBs employed in the activation of 1, [1][2][3] with the use of carbanions (R À ) having much less precedent, [4][5][6][7][8][9] despite the ability of carbanions to generate amore nucleophilic {BPin} moiety owing to their greater basicity relative to alkoxides and NHCs.Among the limited examples in this area, recent studies have shown that complex A synthesised from 1 and nBuÀMgL (L = bdiketiminato) transfers aboryl anion to boranes to form new unsymmetrical sp 2 Àsp 3 diboranes (Scheme 1a). [10] Indeed, transfer of ab oryl nucleophile to an external electrophile is the dominant reactivity pathway reported for B 2 Pin 2 activated by simple carbanions.…”

Reaction of B2(o‐tol)4 with CO and Isocyanides: Cleavage of the C≡O Triple Bond and Direct C−H Borylations

“…[3p, 6] Bis(pinacolato)diborane (B 2 pin 2 ), which is stabilized by pp-pp interactions from four adjacent oxygen atoms,h as been widely used for transition-metal-catalyzed borylations of organic molecules. [8] Thea bsence of heteroatoms at one of the two boron atoms renders this molecule highly electrophilic.Infact, pinBÀBMes 2 reacts with tert-butylisocyanide leading to cleavage of the NCt riple bond, [8] with CO to provide aC O-coordinated boraalkene, [8] with alkynes to form diborylalkenes, [9] with 2,6-dimethylphenylisocyanide to furnish a1 ,2-oxaboretane ring, [10] with pyridine to give C À Hf unctionalized pyridines, [11] and with electrons to afford the corresponding radical anion. [8] Thea bsence of heteroatoms at one of the two boron atoms renders this molecule highly electrophilic.Infact, pinBÀBMes 2 reacts with tert-butylisocyanide leading to cleavage of the NCt riple bond, [8] with CO to provide aC O-coordinated boraalkene, [8] with alkynes to form diborylalkenes, [9] with 2,6-dimethylphenylisocyanide to furnish a1 ,2-oxaboretane ring, [10] with pyridine to give C À Hf unctionalized pyridines, [11] and with electrons to afford the corresponding radical anion.…”

Substrate‐Assisted, Transition‐Metal‐Free Diboration of Alkynamides with Mixed Diboron: Regio‐ and Stereoselective Access to trans‐1,2‐Vinyldiboronates

“…As such, vinylboronic acid derivatives bearing multiple boron moieties with chemoselective reactivity are highly desirable. For example,p hotocatalyzed diborations in the presence of ac atalytic amount of diphenyl disulfide under light irradiation, [7] and diborations employing strongly Lewis acidic, unsymmetrical diborane (pinBBMes 2 ), [8] afford the 1,2-diborylalkenes as amixture of E-and Z-configured products. [6] Recently,m etal-free conditions have been reported.…”

“…[6] Recently,m etal-free conditions have been reported. For example,p hotocatalyzed diborations in the presence of ac atalytic amount of diphenyl disulfide under light irradiation, [7] and diborations employing strongly Lewis acidic, unsymmetrical diborane (pinBBMes 2 ), [8] afford the 1,2-diborylalkenes as amixture of E-and Z-configured products.…”