Palladium-catalyzed regioselective hydroboration of aryl alkenes with B₂pin₂

Abstract

A palladium(ii)-catalyzed hydroboration of aryl alkenes with stable and easy-to-handle (pinacolato)diboron (Bpin) under mild conditions has been developed. Acetic acid acted as the solvent and the hydrogen source, which has been identified by deuterium experiments. Notably, isomerization-hydroboration of allyl benzene derivatives was observed. As a result, a series of benzyl boronic esters were obtained in moderate to excellent yields with exclusive regioselectivity.

H2‐Acceptorless Dehydrogenative Boration and Transfer Boration of Alkenes Enabled by Zirconium Catalyst

“…Alternatively,t he direct dehydrogenative boration of readily available alkenes is an attractive methodology to prepare VBEs. [5,11] Yetless successful examples were reported due to the overwhelming hydroboration activities of borane using Rh, [12] Ir, [13] Pd, [14] Ni, [15] Co, [16] and Fe catalysts [17] to produce saturated alkyl boronate esters.N evertheless,w hen aRhcatalyst [18] was chosen, the dehydrogenative boration of alkenes was achieved in the presence of sacrificial alkenes or at higher temperatures (50-150 8 8C) (Scheme 1a). Recently,an iron-catalyzed dehydrogenative boration was reported, in which 2equivalents of norbornene were required.…”

Cu-catalyzed deoxygenative gem-hydroborylation of aromatic aldehydes and ketones to access benzylboronic esters

“…Directly utilizing benzylic C-H as the electrophile under the transition metal catalyzed borylation condition is an ideal approach, while it currently still suffers from the chemoselectivity issues on benzylic or aromatic C-H borylation and mono-or di-borylation [28][29][30]. Styrenes could also be used for the syn-thesis of benzylboronic esters via unusual transition metal catalyzed Markovnikov selective hydroborations [31][32][33][34][35][36][37]. Through 1,2-metelate rearrangement, benzylboronic esters could be synthesized from tosylhydrazones and HBpin or B2pin2 under a metal-free condition [38].…”

Hydroboration of Alkenes and Alkynes Employing Earth‐Abundant Metal Catalysts

“…Metal‐catalyzed hydroboration employing boronic esters is an attractive alternative because of the relative stability of the products formed while still retaining subsequent reactivity. Excellent regio‐ and chemoselectivity have been achieved using precious metal catalysts based on Ir, Rh, Ru, and Pd and even main group metals like Al in the hydroboration of alkenes and alkynes. The limited availability, high and volatile cost of precious metal catalysts, and their toxicity has shifted the focus more recently towards the development of cheap, sustainable and environmentally benign first row metal alternatives…”