Photocatalytic Generation of β-Fluoroalkylated α-Carbonyl Carbocations

Abstract

Nucleophilic addition to α,β-unsaturated carbonyl compounds normally occurs at the carbonyl carbon or β-carbon. The direct α-nucleophilic addition at the α-carbon can hardly be achieved due to electronic mismatch. In this work, we report the nucleophilic addition of β-fluoroalkyl α-carbonyl carbocations that are prepared via CBZ6-induced redox-neutral photocatalysis. In this process, the photocatalytic oxidation of the β-fluoroalkyl α-carbonyl radical to the corresponding carbocation is the key step. The β-fluoroalkyl α-carbonyl radical is generated in situ by the addition of a polyfluoroalkyl radical, which is generated by the photocatalytic fragmentation of polyfluoroalkyl sulfonyl chloride, to α,β-unsaturated carbonyls. The high E₀₀ value of CBZ6 (3.19 V vs the saturated calomel electrode), which corresponds with the absorbed photoenergy, contributes to the high catalytic reactivity.