Visible‐Light‐Mediated Charge Transfer Enables C−C Bond Formation with Traceless Acceptor Groups

Abstract

The development and application of traceless acceptor groups in photochemical CÀCb ond formation is described. This strategy was enabledb yt he photoexcitation of electron donor-acceptor (EDA) complexes with visible light. The traceless acceptors,w hich were readily prepared from amino acid and peptide feedstocks, could be used to alkylate aw ide range of heteroarene and enamine donors under metal-a nd peroxide-free conditions. The crucial role of the EDA complexes in the mechanism of these reactions was explored through combined experimental and computational studies.Scheme1.Photochemical CÀCb ond formationw ith EDA complexes.[a] Dr.

Visible‐Light‐Promoted C(sp3)−H Alkylation by Intermolecular Charge Transfer: Preparation of Unnatural α‐Amino Acids and Late‐Stage Modification of Peptides

“…In the past few years, photoinduced radical reactions through intermolecular charge transfer have attracted much attention . Very recently, Glorius and co‐workers disclosed a novel photoinduced radical addition‐elimination process for alkylation of indole C(sp 2 )−H bonds . In the reaction, SET is mediated by a photoactive Katritzky‐salt‐based electron donor‐acceptor (EDA) complex under catalyst‐free conditions (Scheme b).…”

Pyridinium Salts as Redox‐Active Functional Group Transfer Reagents

“…In principle,t he concept of PET could be applicable to adiverse array of substrates which form EDAcomplexes with pyridinium salts.A ne xample of this is the recently reported alkylation of indoles using amino acid derived pyridinium salts in the presence of an amine base, [55] as well as the use of 1 in the ipso-alkylation of vinylboronic acids. [56]…”

Visible‐Light‐Promoted C(sp3)−H Alkylation by Intermolecular Charge Transfer: Preparation of Unnatural α‐Amino Acids and Late‐Stage Modification of Peptides

“…Based on the above investigations and previous reports, [12][13][14][15] we proposed a possible mechanism for this reaction (Scheme 4). Firstly, a colored EDA complex was formed in the presence of 1 a and 2 a (a ternary EDA complex might form in the presence of DBU).…”

“…[12] Very recently, Glorius and co-workers disclosed a novel photoinduced radical addition-elimination process for alkylation of indole C(sp 2 ) À H bonds. [13] In the reaction, SET is mediated by a photoactive Katritzky-salt-based electron donor-acceptor (EDA) complex under catalyst-free conditions (Scheme 1 b). At the same time, the group of Aggarwal reported a series of photoredox reactions, such as Giese-type Michael addition and radical addition-elimination of unsaturated sulfone reagents, induced by Katritzky-saltbased EDA complexes (Scheme 1 b).…”