Transition-Metal-Free Borylation of Allylic and Propargylic Alcohols

Transition-metal-free synthesis of vicinal triborated compounds and selective functionalisation of the internal C–B bond

1,2,3-Triborated compounds can be prepared by simple nucleophilic borylation of 1,3-dienes, without the assistance of metal catalysts.

Collective Syntheses of 2-(3-Methylbenzofuran-2-yl)phenol-Derived Natural Products by a Cascade [3,3]-Sigmatropic Rearrangement/Aromatization Strategy

A cascade [3,3]-sigmatropic rearrangement/aromatization strategy to the synthesis of 2-(3-methylbenzofuran-2-yl)phenol derivatives was developed and applied to the collective syntheses of seven 2-arylbenzofuran-containing natural products, namely glycybenzofuran, glycyuralin E, lespedezol A₁, puerariafuran, 7,2',4'-trihydroxy-3-benzofurancarboxylic acid, coumestrol, and 4'-O-methylcoumestrol. Among them, the total syntheses of glycybenzofuran, glycyuralin E, puerariafuran, 7,2',4'-trihydroxy-3-benzofurancarboxylic acid, and 4'-O-methylcoumestrol were reported for the first time. The practicality of this novel strategy in preparation of the key intermediates was demonstrated by performing the reaction on gram scale and by synthesizing a series of natural products with 2-(3-methylbenzofuran-2-yl)phenol scaffolds in a common strategy.

Synthesis and Reduction of Sterically Encumbered Mesoionic Carbene-Stabilized Aryldihaloboranes

Sterically hindered, in situ generated 1,3,4-substituted 1,2,3-triazol-5-ylidene mesoionic carbenes (MICs) were employed to stabilize a number of aryl- and heteroaryldihaloboranes, as well as the first MIC-supported diborane. Reduction of borane adducts of the 1-(2,6-diisopropylphenyl)-3-methyl-4-tert-butyl-1,2,3-triazol-5-ylidene ligand with KC₈ in non-coordinating solvents led to intramolecular C-H- and, C-C-activation at an isopropyl residue of the supporting ligand. DFT calculations showed that each of these activation reactions proceeds via a different isomer of a borylene intermediate.

Iron-catalyzed boration of allylic esters: an efficient approach to allylic boronates

The first general iron-catalyzed boration of allylic esters has been developed.

Copper-catalyzed/mediated borylation reactions of epoxides with diboron reagents: access to β-hydroxyl boronic esters

We report the first copper-catalyzed/mediated borylative ring opening reaction of epoxides.

An expedient E-stereoselective synthesis of multi-substituted functionalized allylic boronates from Morita–Baylis–Hillman alcohols

Various functionalized tri-substituted allylic boronates were synthesized through borylation of Morita–Baylis–Hillman alcohols under the catalysis of Cu(OTf)₂ at ambient temperature_.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.

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

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.

Transition-Metal-Free Borylation of Allylic and Propargylic Alcohols

The base-catalyzed allylic borylation of tertiary allylic alcohols allows the synthesis of 1,1-disubstituted allyl boronates, in moderate to high yield. The unexpected tandem performance of the Lewis acid-base adduct, [Hbase](+) [MeO-B2 pin2 ](-) favored the formation of 1,2,3-triborylated species from the tertiary allylic alcohols and 1-propargylic cyclohexanol at 90 °C.