β‐Selective Aroylation of Activated Alkenes by Photoredox Catalysis

Abstract

Late-stage synthesis of a,b-unsaturated aryl ketones remains an unmet challenge in organic synthesis.R eported herein is aphotocatalytic non-chain-radical aroyl chlorination of alkenes by a1,3-chlorine atom shift to form b-chloroketones as masked enones that liberate the desired enones upon workup.T his strategy suppresses side reactions of the enone products.T he reaction tolerates aw ide array of functional groups and complex molecules including derivatives of peptides,s ugars,n atural products,n ucleosides,a nd marketed drugs.N otably,a ddition of 2,6-di-tert-butyl-4-methyl-pyridine enhances the quantum yield and efficiency of the crosscoupling reaction. Experimental and computational studies suggest amechanism involving PCET,formation and reaction of an a-chloro-a-hydroxy benzyl radical, and 1,3-chlorine atom shift.

Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

“…A reaction quantum yield of 0.15-0.3 is in good agreement with other studies on non-radical chain propagation reactions, where typical quan-Quantum Yield = moles of product moles of incident photons tum yields of photoredox reactions can range from .19 to .43. [48][49][50] Ellman and coworkers partly explored the mechanism of a closely related αamino arylation reaction involving substituted piperidine analogues and observed 0.4-0.6 at early timescales, 46 which is in relatively good agreement with our quantum yields. These results were collected without the use of insoluble sodium acetate, which actinometry experiments suggest scatter 10-20% of incoming photons.…”

Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

“…A reaction quantum yield of 0.15-0.3 is in good agreement with other studies on non-radical chain propagation reactions, where typical quantum yields of photoredox reactions can range from 0.19 to 0.43. [46][47][48] Ellman and coworkers partly explored the mechanism of a closely related α-amino arylation reaction involving substituted piperidine analogues and observed 0.4-0.6 at early timescales, 44 which is in relatively good agreement with our quantum yields. These results were collected without the use of insoluble sodium acetate, which may explain the higher quantum yield.…”

Visible‐Light Photoredox‐Catalyzed Acyl Lactonization of Alkenes with Acyl Chlorides

“…Later, the same group developed an elegant organic photoredox‐catalyzed α ‐C(sp 3 )−H aroylation of amines with acyl chlorides [9] . Ngai and coworkers reported a photocatalytic regioselective chloro aroylation of activated alkenes to form β ‐chloroketones as masked enones that delivered aryl enones upon workup [10] . Oh and coworkers reported a photocatalytic chloroacylation of alkenes with acyl chlorides [11] .…”