Divergent Synthesis of Vinyl‐, Benzyl‐, and Borylsilanes: Aryl to Alkyl 1,5‐Palladium Migration/Coupling Sequences

Abstract

Organosilicon compounds have been extensively utilized both in industry and academia. Studies on the syntheses of diverse organosilanes is highly appealing. Through‐space metal/hydrogen shifts allow functionalization of C−H bonds at a remote site, which are otherwise difficult to achieve. However, until now, an aryl to alkyl 1,5‐palladium migration process seems to have not been presented. Reported herein is the remote olefination, arylation, and borylation of a methyl group on silicon to access diverse vinyl‐, benzyl‐, and borylsilanes, constituting a unique C(sp3)−H transformation based on a 1,5‐palladium migration process.

Borylation of Unactivated C(sp3)–H Bonds with Bromide as a Traceless Directing Group

“…Among the used TDGs, halide is an important member and has been successfully applied in several transformations . Very recently, Zhao and coworkers demonstrated an alkyl C–H borylation reaction directed by naphthyl bromide (Scheme b) . In their work, the C–H bond is supposed to be activated by the α-effect of the silicon atom, and no borylation product was observed with the more inert C–H bond of the carbon analogue.…”

Metal-catalysed C–H bond activation and borylation

“…In 2020, Zhao and co-workers demonstrated 193 a palladium-catalysed approach for the preparation of various important borosilanes that are otherwise difficult to make (Scheme 78).…”

“…Very recently, the Lin group, inspired by Zhao's work, 193 reported a similar type of Pd-catalysed aliphatic borylation using bromine as a traceless directing group (Scheme 79). 194 The reaction was said to proceed via a 1,5-Pd migration.…”

Quadruple Role of Pd Catalyst in Domino Reaction Involving Aryl to Alkyl 1,5‐Pd Migration to Access 1,9‐Bridged Triptycenes

“…1,5‐Pd migration is considered to involve both the concerted Pd II and stepwise Pd IV pathways, the latter proceeding via pallada IV cycle B . Although reactions occurring via Pd migration have been widely reported, [14] the majority of these involve 1,4‐Pd migration, [15] with 1,5‐Pd migration being limited to only three examples, [16] namely vinylic to aryl, [16a,b] aryl to aryl, [16c–e,g] and aryl to Si‐alkyl migration [16f] . This is likely due to the difficulty in forming six‐membered palladacycles, and/or because reductive elimination of the five‐membered product occurs more readily than 1,5‐Pd migration.…”