Electrocatalytic Dehydrogenative Esterification of Aliphatic Carboxylic Acids: Access to Bioactive Lactones

Abstract

A scalable and efficient electrocatalytic dehydrogenative esterification is reported. With an indirect electrolysis strategy, both intra- and intermolecular-type reactions were amenable to this practical method. With n-BuNI as the catalyst, undesired decarboxylation and Baeyer-Villiger oxidation were suppressed. More importantly, this novel method provided reliable and direct access to the natural product cytosporanone A on a gram scale.

Electrocatalytic Oxidative Transformation of Organic Acids for Carbon–Heteroatom and Sulfur–Heteroatom Bond Formation

“…In 2019, Terent'ev and co‐workers reported an electrochemically induced, intermolecular, cross‐dehydrogenative C−O coupling of β‐diketones and β‐ketoesters with carboxylic acids by using KBr as a supporting electrolyte (Scheme ) . They proposed that brominated β‐diketones or β‐ketoesters served as an important intermediates in this reaction, similar to that reported by Xu et al …”

“…In light of the competing decarboxylation of aliphatic acids, it would be significant to construct ester C−O bonds from aliphatic acids to suppress this side reaction. In 2017, Xu and co‐workers reported the intra‐ and intermolecular electrocatalytic dehydrogenative esterification of carboxylic acids with ketones by using an indirect electrolysis strategy (Scheme ) …”

“…In 2017, Xu and coworkers reported the intra-and intermoleculare lectrocatalytic dehydrogenative esterification of carboxylic acids with ketones by using an indirect electrolysis strategy (Scheme 6). [16] For intermolecular dehydrogenative esterification, both aliphatic and aromatic acids were well tolerated. The mechanism given in Scheme 7w as proposed.…”

C−O coupling of Malonyl Peroxides with Enol Ethers via [5+2] Cycloaddition: Non‐Rubottom Oxidation

“…In regard to the oxyfunctionalization of carbonyl targets, they were previously limited to the alkoxy, peroxy, oxygen‐sulfonyl, oxygen‐phosphoryl, aminoxy groups. In a few studies α‐acyloxy‐carbonyl products were synthesized using Cu/CuI/air, Cu(acac) 2 /TBHP, CuI/O 2 , Pybox‐Cu(II) complex/K 4 [Fe(CN) 6 ], TBAI/H 2 O 2 or TBAI/TBHP, hypervalent iodine compounds, N ‐methyl‐ O ‐benzoylhydroxylamine hydrochloride, or TBAI/electric current . Apart from these reports, α‐oxygenation of mono‐carbonyl compounds were achieved by hydroxylation and alkoxylation of silyl enol ethers, hydroxylation and alkoxylation of alkyl enol ethers or enolates .…”

“…In a few studies α-acyloxy-carbonyl products were synthesized using Cu/CuI/air, [51] Cu(acac) 2 /TBHP, [52] CuI/O 2 , [53] Pybox-Cu(II) complex/K 4 [Fe(CN) 6 ], [54] TBAI/H 2 O 2 [55] or TBAI/TBHP, [56] hypervalent iodine compounds, [57] N-methyl-O-benzoylhydroxylamine hydrochloride, [58] or TBAI/electric current. [59] Apart from these reports, α-oxygenation of mono-carbonyl compounds were achieved by hydroxylation [60] and alkoxylation [61] of silyl enol ethers, hydroxylation [62] and alkoxylation [61c,63] of alkyl enol ethers or enolates. [64] All these processes of oxyfunctionalization require addition of an external oxidant into the reaction, which usually plays oxygen-atom transfer role, as well as the removal of oxidant residual and catalysts after the reaction.…”