Radical-polar crossover reactions of vinylboron ate complexes

Abstract

Vinyl boronic esters are valuable substrates for Suzuki-Miyaura cross-coupling reactions. However, boron-substituted alkenes have drawn little attention as radical acceptors, and the radical chemistry of vinylboron ate complexes is underexplored. We show here that carbon radicals add efficiently to vinylboron ate complexes and that their adduct radical anions undergo radical-polar crossover: A 1,2-alkyl/aryl shift from boron to the α-carbon sp center provides secondary or tertiary alkyl boronic esters. In contrast to the Suzuki-Miyaura coupling, a transition metal is not required, and two carbon-carbon bonds are formed. The valuable boronic ester moiety remains in the product and can be used in follow-up chemistry, enlarging the chemical space of the method. The cascade uses commercial starting materials and provides access to perfluoroalkylated alcohols, γ-lactones, γ-hydroxy alkylnitriles, and compounds bearing quaternary carbon centers.

Enabling the Cross-Coupling of Tertiary Organoboron Nucleophiles through Radical-Mediated Alkyl Transfer

“…The clear absence of methods predicated on the use of bench-stable partners inspired the laboratory to explore tertiary organoboron nucleophiles more closely – especially given the recent surge in methods for their preparation. 10 …”

“…Given the growing suite of methods for the synthesis of tertiary organoboron compounds, 10 this photoredox cross-coupling serves as a timely addition, enabling tertiary organoboron reagents as partners in the installation of arylated quaternary centers. Although limitations remain, the ligand screening data and mechanistic interrogation will allow practitioners seeking to employ other tertiary radical feedstocks (carboxylic acids, halides, aldehydes, silicates, etc.)…”

Intermolecular Formation of Two C−C Bonds across Olefins Enabled by Boron‐Based Relay Strategies

“…[6] In comparison to reactions with sp 2 -electrophiles,t ransition-metal-catalyzed coupling reactions with sp 3 -electrophiles are significantly more difficult because of slower oxidative addition and significantly more facile b-hydride elimination. Therefore,o ther means based on different reactive species appear more promising.T he Studer [7] and Aggarwal [8] groups have now shown independently that direct alkylarylation or dialkylation reactions of vinylboronates are indeed possible by applying aradical-polar crossover strategy (Schemes 3a nd 4).…”

Aus Drei mach Eins

“…Das so entstehende Radikalanion unterliegt einer radikalisch‐ionischen Kreuzungsreaktion und lagert sich dabei um. Diese 1,2‐R‐Wanderung eines Alkyl‐ oder Aryl‐Restes vom Bor‐Atom zum α‐Kohlenstoff‐Atom eröffnet den Zugang zu sekundären oder tertiären Alkylboronsäureestern .…”