Chromium-Catalyzed Selective Borylation of Vinyl Triflates and Unactivated Aryl Carboxylic Esters with Pinacolborane

Abstract

The use of pinacolborane to borylate abundant vinyl triflates and unactivated aryl carboxylic esters was enabled by chromium catalysis via the selective formation of vinyl and aryl boronate esters. The competing hydrided reduction or allylic borylation proceeds sluggishly or does not occur, therefore providing a selective strategy for the incorporation of boronate into olefins and arenes. Mechanistic studies indicate that the σ-bond metathesis or oxidative addition mechanism may be considered to be responsible for the cleavage of ester scaffolds.

Access to C(sp3) borylated and silylated cyclic molecules: hydrogenation of corresponding arenes and heteroarenes

“…The solution was concentrated by rotary evaporation, puried using ash column chromatography with hexane/ethyl acetate (2-4% gradient) solvents and concentrated and dried by rotary evaporation to yield a white solid (193 mg, 66% yield). 1 64 Synthesis of starting materials via lithiation, silylation and borylation (1y, 1x, 1ab, 1ac, 1ad) 2-Chloro-6-(triuoromethyl)-3-(trimethylsilyl)pyridine (1y). Synthesis of 1y was carried out using the reported literature procedure.…”

Iron‐Catalyzed Reductive C(aryl)—Si Cross‐Coupling of Diaryl Ethers with Chlorosilanes

“…[ 35‐41 ] In particular, the direct functionalization of C(aryl)—O bond of aryl ethers is important for the transformation of oxygen‐rich lignocellulosic plant biomass like lignin to well‐defined aromatic compounds. Despite great interest and recent advance on catalytic C(aryl)—O activation of aryl alkyl ethers [ 42‐52 ] and hydrogenolysis of diaryl ether C(aryl)—O bonds (Scheme 1b), [ 53‐57 ] the chemo‐ and regioselective functionalization of the C(aryl)—O bonds of diaryl ethers, especially highly substituted biaryl ethers relevant to those found in lignin, has remained a challenge. Therefore, the development of a selective and efficient catalysis for tackling this challenge is an attractive research object.…”

Bipyridine Ligand-Promoted cis-Selective Hydroboration of Alkynes with Chromium Catalysis

“…[14] We recently disclosed that the in-situ formed low-valent Cr species shows the ability in promoting the borylation of aryl and vinyl esters by reaction with pinacolborane. [15] It is anticipated that the addition of pinacolborane to alkynes may occur with Cr catalysis by initially insertion of H-Bpin bond and followed by addition across triple bonds in affording vinylboronate esters. Herein, we report the hydroboration of alkynes that could be catalyzed chromium by using catalytic amount of metallic magnesium as reductant for the in-situ generation of reactive species, providing a strategy to access to olefinated boronate esters at ambient temperature (Scheme 1b).…”