The Impact of Boron Hybridisation on Photocatalytic Processes

Abstract

Recently the fruitful merger of organoboron chemistry and photocatalysis has come to the forefront of organic synthesis, resulting in the development of new technologies to access complex (non)borylated frameworks. Central to the success of this combination is control of boron hybridisation. Contingent on the photoactivation mode, boron as its neutral planar form or tetrahedral boronate can be used to regulate reactivity. This Minireview highlights the current state of the art in photocatalytic processes utilising organoboron compounds, paying particular attention to the role of boron hybridisation for the target transformation.

A General Three-Component Alkyl Petasis Boron–Mannich Reaction

“…Benzene isosteres, such as bicyclo[1.1.1]pentane (BCP) (39), adamantane (40) could also be efficiently installed, which can potentially provide an approach for rapid scaffold hopping of bioactive phenyl amines synthesized with classic PBM reaction using phenyl boronic acids. Sterically hindered quaternary carbons and architecturally complex structures, often incorporated in bioactive small molecules to enhance potency, selectivity, and metabolic stability through enriching threedimensionality, 11 were also addressed.…”

“…This tactic aims to provide a universal solution for the APBM reaction (Figure D). On investigating the oxidative potentials of various alkylboron ate-complex species (Figure E), − catechol installation was identified as a mild method to activate boron without the need for strong bases. − Therefore, the corresponding alkyl boronate complexes with low oxidative potentials ( E p = ∼0.49 V, versus a saturated calomel electrode (SCE)) were anticipated to undergo facile single-electron oxidation (Figure E). Since the photoexcited iminium ions were found to function as strong oxidants, , it was postulated that the in situ generated catechol boron ester ate-complexes could be oxidized, resulting in the generation of alkyl radicals.…”

Electrochemical Generation of Aryl Radicals from Organoboron Reagents Enabled by Pulsed Electrosynthesis

“…[13] However, the quaternization of the boron center to a boronate complex significantly lowers their oxidation potential and had found successful application in photoredox reactions. [26] Our initial cyclic voltammetry studies (Figure 2B) using p-anisyl potassium trifluoroborate S2, for details.…”