Photochemically Promoted Transition Metal-Free Cross-Coupling of Acylsilanes with Organoboronic Esters

Abstract

Intermolecular carbon-carbon bond formation between acylsilanes and organoboronic esters was achieved by photoirradiation under almost neutral, transition metal-free conditions. In this reaction, siloxycarbenes generated by photoisomerization of acylsilanes reacted with boronic esters to give the formal B-C bond insertion intermediates, which underwent unique rearrangement to afford the cyclic R-alkoxyboronic esters. Acidic treatment of the resulting crude products under air furnished the crosscoupled ketones in good yields.

Lewis Acid‐Assisted Photoinduced Intermolecular Coupling between Acylsilanes and Aldehydes: A Formal Cross Benzoin‐Type Condensation

“…This carbene formation is potentially useful for carbene‐mediated synthetic reactions, but applications of this methodology to intermolecular carbon–carbon bond‐forming reactions are rather limited. On the other hand, we have reported novel photoinduced intermolecular cross coupling of acylsilanes 1 with boronic esters, which involves nucleophilic addition of photochemically generated siloxycarbenes 2 onto electrophilic boron centers . This result prompted us to develop photoinduced cross benzoin‐type reaction for preparation of α‐hydroxyketones by utilizing siloxycarbenes as an acyl anion equivalent.…”

Transition Metal‐Free ipso‐Functionalization of Arylboronic Acids and Derivatives

“…[42] The reaction was irradiated by a 500-W super high-pressure Hg lamp. The authors hypothesized a carbene-involved pathway.…”

Synthesis of silacyclopent-2-en-4-ols via intramolecular [2 + 2] photocycloaddition of benzoyl(allyl)silanes

“…The handling of acylsilanes requires special precautions as they are known to undergo Brook rearrangement to a reactive carbene after photoirradiation or thermal conditions. This carbene has been shown to undergo insertion reactions in polarised heteroatomhydrogen bounds, 48,49 cycloadditions to aldehydes 50 and alkynes, 51,52 cross-coupling reaction with organoboronic esters 53 and even C-H insertions [54][55][56] under harsher conditions. Carbene formation and its subsequent reactions are then possible competitive destructive pathways to the [2 + 2] photocycloaddition.…”