Radical Strategy for the Transition-Metal-Catalyzed Synthesis of γ-Lactones: A Review

Abstract

The γ-lactone skeleton is very important component of various natural products, biological molecules, food additives, and perfumes. As a result, much effort has been made towards such compounds. In this review, we summarize recent progress in transition-metal-catalyzed annulation reactions for the formation of γ-lactone derivatives through a radical pathway. Various reagents, such as anhydrides, Togni’s reagent, TMSN3, arenesulfonyl chlorides, arenediazonium salts, dibenzoyl peroxides, O-benzoylhydroxylamine, NFSI, and α-halocarboxylic compounds, used in radical cyclization reactions are described, and the mechanisms of these radical annulation reactions are also discussed.1 Introduction2 Annulations of Alkenes with Anhydrides3 Annulations of Unsaturated Carboxylic Acids with Nucleophiles4 Annulations of Alkenes with α-Halocarboxylic Compounds5 Conclusions and Outlook

Metal-Catalyst-Controlled Divergent Synthesis of γ-Butyrolactones via Intramolecular Coupling of Epoxides with Alcohols

“…Additionally, the construction of γ-butyrolactones from the cyclization of alkenyl carboxylic acids also provides a powerful avenue, affording the desired γ-lactones with high efficiency and good functionality tolerance . Furthermore, intermolecular coupling of unsaturated hydrocarbons with CO 2 or annulation reactions of alkenes were documented by previous research. Despite great advances in these strategies mentioned above, external strong acid or toxic carbon monoxide is always needed, and divergent synthesis of α- and β-substituted γ-lactones from identical raw materials remains a challenge.…”

Visible-Light-Induced Photoredox-Catalyzed Selective 1,4-Difluoroalkylesterification of 1-Aryl-1,3-dienes

“…3-Substituted benzobutyrolactones are an attractive class of oxygen-containing structural motifs prevalent in numerous biologically active compounds, and their synthesis attracts growing interest . We surmised that an intramolecular version, such as 1,4-difluoroesterification of 1-(1,3-butadienyl)­benzoic acids, would be complementary to extant methods, allowing construction of structurally diverse 3-difluoroalkylated benzobutyrolactones.…”

“…On the basis of mechanistic studies (Supporting Information, section 6) and literature reports, , a possible mechanism involving a dual photoredox/copper catalytic cycle is proposed with the model reaction as an example (Scheme ). First, upon visible-light irradiation, the in situ formed strongly reducing excited state Ir­(III)* ( E 1/2 [Ir­(IV)/Ir­(III)*] = −1.73 V vs SCE in CH 3 CN) undergoes a thermodynamically favorable SET process with methyl bromodifluoroacetate 2a to generate difluoroalkyl radical 2a-I and the oxidized state Ir­(IV) ( E 1/2 [Ir­(IV)/Ir­(III)] = 0.77 V vs SCE in CH 3 CN) .…”