Trans-Diborylation of Alkynes:Pseudo-Intramolecular Strategy Utilizing a Propargylic Alcohol Unit

Abstract

We present the first trans-selective diborylation reaction of alkynes. By means of theoretical calculation-assisted reaction analysis, we designed a pseudo-intramolecular reaction of diboron, propargyl alcohol, and a base to facilitate B-B bond activation and C-B bond formation with high efficiency. This approach provides synthetically versatile and densely functionalized 4-borylated 1,2-oxaborol-2(5H)-oles (vinyldiboronates) in a straightforward manner. Detailed computational analysis showed that the directing alkoxide functionality markedly lowers the activation energy of B-C bond formation.

Mechanism of NHC-Catalyzed Conjugate Additions of Diboron and Borosilane Reagents to α,β-Unsaturated Carbonyl Compounds

“…22 Activation of B–B bonds by an external 23 and then a neighboring Lewis basic alkoxide 24 were later exploited to effect diboron additions to unactivated alkenes, and related transformations involving propargyl alcohols were outlined. 25 Metal alkoxides have been shown to catalyze reactions of silylboron reagents with organohalide substrates, affording the corresponding silanes. 26 In the significant majority of Lewis base catalyzed boryl and silyl additions, the presence of a proton source (typically MeOH) is necessary; 16a in many instances, excess base is needed for optimal efficiency and/or stereoselectivity.…”

Homolytic Cleavage of a B−B Bond by the Cooperative Catalysis of Two Lewis Bases: Computational Design and Experimental Verification

“…[3,4] On the other hand, transitionmetal-free catalytic systems for activating the BÀB bond of diborane compounds have also attracted much attention. [5][6][7][8][9] It has been shown that diborane compounds became asource of nucleophilic boryl moiety,w hen one of the boron atoms of the diborane was tetracoordinated to as trong base (Scheme 1a). [5][6][7][8][9] It has been shown that diborane compounds became asource of nucleophilic boryl moiety,w hen one of the boron atoms of the diborane was tetracoordinated to as trong base (Scheme 1a).…”

“…When B 2 (pin) 2 (2)w as added to aT HF solution of 4-cyanopyridine,aspectrum at g = 2.00319 (298 K) was obtained, as shown in Figure 2. Interestingly,i nt he chemistry of frustrated Lewis pairs (FLP) [15] or chemistry containing Lewis adduct of sp 2 -sp 3 diboranes, [5][6][7][8][9] the Lewis bases are always regarded as an electron donor. Interestingly,i nt he chemistry of frustrated Lewis pairs (FLP) [15] or chemistry containing Lewis adduct of sp 2 -sp 3 diboranes, [5][6][7][8][9] the Lewis bases are always regarded as an electron donor.…”

Allylic borylation of tertiary allylic alcohols: a divergent and straightforward access to allylic boronates

“…6 This unique reactivity of electronically unactivated alkynes with a boryl anion equivalent was achieved 6 This unique reactivity of electronically unactivated alkynes with a boryl anion equivalent was achieved…”