Visible-light-induced radical cascade reaction to prepare oxindoles via alkyl radical addition to N-arylacryl amides

Abstract

A photochemical approach towards oxindoles with C3 quaternary centers by the radical cascade reaction of α,β-unsaturated N-arylacryl amides with alkyl bromides or iodides upon visible light irradiation under mild reaction conditions was developed.

Visible-Light-Induced Photoredox 1,2-Dialkylation of Styrenes with α-Carbonyl Alkyl Bromides and Pyridin-1-ium Salts

“…Consequently, the possible mechanism for this alkene dialkylation protocol was proposed (Scheme ). − The alkyl radical intermediate A is formed directly by single-electron transfer between α-carbonyl alkyl bromide 2a and the [Ru­(bpy) 3 ] 2+ * intermediate, which is irradiated of the [Ru­(bpy) 3 ] 2+ species by blue LED light. , Addition of the alkyl radical intermediate A across the CC bond of alkene 1 affords the new alkyl radical intermediate B , followed by addition to pyridin-1-ium salt 3 to form the alkylated pyridin-1-ium radical cation intermediate C . , Finally, single electron oxidation and dealkylation of intermediate C afford the desired product 4 .…”

“…α-Carbonyl alkyl bromides are commonly versatile synthetic building blocks that can be applied to a wide spectrum of reliable derivatizations, which have been utilized as the alkyl radical precursors to allow various alkene difunctionalization reactions, including alkylarylation, alkylamination, alkyloxygenation, and others . To the best of our knowledge, however, examples of alkene dialkylation with α-carbonyl alkyl bromides as the alkyl radical precursors have never been reported.…”

Annulation Cascades of Cyclosulfonium Salts and Alkenes towards Sulfur‐Containing N‐Heterocycles by Visible Light/Copper Catalysis

“…[ 11 ] Nevertheless, developing alkyl radical addition/cyclization of N ‐arylacrylamides with readily available materials still remains a huge challenge. In this respect, the alkyl electrophiles mainly focus on alkanes, [ 12 ] alkyl halides, [ 13 ] hypervalent iodine derivative, [ 14 ] carboxylic acids, [ 15 ] aldehydes, [ 16 ] cycloketone oxime esters, [ 17 ] and katritzky salts [ 18 ] (Scheme 1b). Therefore, it is still highly desirable to develop new alkyl electrophiles for the synthesis of oxindoles through a radical addition/cyclization reaction.…”