Photocatalytic Difunctionalization of Vinyl Ureas by Radical Addition Polar Truce–Smiles Rearrangement Cascades

Abstract

We report tandem alkyl‐arylations and phosphonyl‐arylations of vinyl ureas by way of a photocatalytic radical‐polar crossover mechanism. Addition of photoredox‐generated radicals to the alkene forms a new C−C or C−P bond and generates a product radical adjacent to the urea function. Reductive termination of the photocatalytic cycle generates an anion that undergoes a polar Truce–Smiles rearrangement, forming a C−C bond. The reaction is successful with a range of α‐fluorinated alkyl sodium sulfinate salts and diarylphosphine oxides as radical precursors, and the conformationally accelerated Truce–Smiles rearrangement is not restricted by the electronic nature of the migrating aromatic ring. Formally the reaction constitutes an α,β‐difuctionalisation of a carbon–carbon double bond, and proceeds under mild conditions with visible light and a readily available organic photocatalyst. The products are α,α‐diaryl alkylureas typically functionalized with F or P substituents that may be readily converted into α,α‐diaryl alkylamines.

Radical and Ionic Mechanisms in Rearrangements of o-Tolyl Aryl Ethers and Amines Initiated by the Grubbs–Stoltz Reagent, Et3SiH/KOtBu

“…Generally, Smiles and Truce-Smiles rearrangements proceed through the formation of a spiro intermediate, which subsequently undergoes a ring-opening to yield the product [6,17]. Mechanisms featuring a spiro transition state rather than a spiro intermediate have been proposed [7], with several examples being identified by Clayden et al for the Smiles and Truce-Smiles rearrangements [56][57][58][59][60][61][62]. Concerted reaction pathways have also been identified for other Smiles-type rearrangements [63][64][65].…”

Organic thermally activated delayed fluorescence (TADF) compounds used in photocatalysis

“…155). 345 The excited photocatalyst is proposed to oxidise the trifluoromethylsulfinate anion, yielding the electrophilic trifluoromethyl radical (Fig. 156).…”

Recent Advances in the Smiles Rearrangement: New Opportunities for Arylation

“…Overall, the reaction constructs a quaternary center through the carboarylation of an alkene. [47] Scheme 14 Truce-Smiles rearrangement via a radical-polar crossover reaction…”