α-Borylalkyl radicals: their distinctive reactivity in modern organic synthesis

Abstract

In this review, we emphasise the importance of the generation of α-boryl carbon-centred radicals and their utilisation in synthesis.

Photoredox‐Mediated Reaction of gem‐Diborylalkenes: Reactivity Toward Diverse 1,1‐Bisborylalkanes

“…We posit that one efficient way to form gem ‐diboryl radical ( II ) can be achieved by adding carbon‐centered radicals to gem ‐diborylalkenes 2 as described in Scheme F. An analogous alkylation via generating α‐monoboryl carbon‐centered radicals IV using vinyl‐boron species III by adding a variety of carbon‐centered radicals to vinyl‐borons III has been reported by Aggarwal, Zard, Morken, Studer, Shi, Molander, and others (See Scheme E) . Considering the fact that gem ‐diboryalkenes ( 2 ) are more electron deficient than vinyl‐borons III are, they ( 2 ) are expected to be suitable candidates for this type of radical addition scenario.…”

“…It is worth emphasizing that the concept of having a radical and an organo‐bismetallic species on the same carbon center, e.g., ( II′ ) is conceptually new, and it has not yet been thoroughly explored. The resulting radical intermediates II are expected to be highly stabilized, since they are flanked by two boronate groups, respectively, each providing one empty p‐orbital (Scheme C) . According to our theoretical calculations of their radical stabilization energy (RSE), one boronate group, e.g., in 3 and 3′ is expected to stabilize an adjacent radical by at least 6.7 kcal mol −1 (Scheme D).…”

“…In all of these cases, they act as a nucleophilic counterpart (e.g., I , Scheme B) that also includes various electrophilic counterparts that participate in alkylation and cross‐coupling reactions using super stoichiometric amounts of strong bases, metals, or transition metal catalysts . However, their radical chemistry (e.g., II ) has rarely been explored, and it can indeed be used to overcome these limitations (Schemes B–C). The novel reactivity of these species toward the radical scenario will create a new class of transformations, leading to a wider diversity of organoborones that could operate under mild and benign conditions, where research is still beginning to develop.…”

“…While we can propose an array of radical generation strategies by adding an R‐radical to the double bond of II (Scheme F), we envisioned that the photoredox chemistry of carboxylic acids may offer a unique reactivity to create a wider diversity of gem ‐diboryl compounds ( 6 ) that could operate under more benign conditions (Scheme F). One more advantage of this method over the other processes is that carboxylic acids are abundant and can be found in natural products, drugs, and bioactive organic molecules.…”

Synthesis of 1,3‐Bis‐(boryl)alkanes through Boronic Ester Induced Consecutive Double 1,2‐Migration

“…1,2-migrations of boron ate complexes have been shown to be highly reliable for CÀC bond construction while retaining the valuable boron moiety in the product. [6,7] In 1967, Zweifel and co-workers first reported 1,2-alkyl/aryl migrations of vinylboron ate complexes induced by electrophilic halogenation (Scheme 1 a). [8] In 2016, Morken and coworkers disclosed the electrophilic palladation-induced 1,2alkyl/aryl migration of vinylboron ate complexes.…”