Visible‐Light‐Induced Decarboxylative Acylation of Pyridine N ‐Oxides with α‐Oxocarboxylic Acids Using Fluorescein Dimethylammonium as a Photocatalyst

Photocatalytic decarboxylation of free carboxylic acids and their functionalization

Visible light mediated decarboxylative functionalization of carboxylic acids and their derivatives has recently emerged as a novel and powerful toolkit for small molecule activation in diverse carbon-carbon and carbon-hetero bond forming reactions. Naturally abundant highly functionalized bench-stable carboxylic acid analogs have been employed as promising alternatives to non-trivial organometallic reagents for mild and eco-benign synthetic transformation with traceless CO2 by-products. In this highlight article, we focus on the development of various photodecarboxylative functionalization strategies along with intra/inter-molecular cyclization via concerted single electron transfer (SET) or energy transfer (ET) pathways. Moreover, widely explored carboxylic acids are systematically classified here into four categories; i.e., α-keto, aliphatic, α,β-unsaturated, and aromatic analogs for a concise overview to the readership. The association of decarboxylative radical species with coupling partners to construct C-C and C-N/O/S/P/X bonds for each analogous acid has been presented in brief.

1O2 mediated synthesis of carbonyl substituted quinoline-2,4(1H,3H)-diones in visible light: 4CzIPN as a reusable photocatalyst

A mild and eco-friendly method for the construction of carbonyl-containing quinoline-2,4(1H,3H)-diones has been developed in the presence of O2, photocatalyzed by reusable 4CzIPN in visible light. The method is transition-metal free, cost-effective, sustainable and gives the products in moderate to high yields.

A visible-light-induced photosensitizer-free decarbonylative Minisci-type reaction

This study presents a green and practical visible-light-induced photosensitizer-free decarbonylative Minisci-type reaction using aldehydes as alkyl radical precursors. The photocatalytic system exhibits a broad substrate scope and synthetically useful yields. Mechanistic experiments revealed that alkyl radicals could be generated through auto-oxidation of aldehydes under irradiation, which is a mild and effective method for achieving late-stage functionalization of N-heteroarenes. Some biologically active N-heteroarenes could be alkylated using this photocatalytic system smoothly.

Decarboxylative C-H silylation of N-heteroarenes with silanecarboxylic acids

Established decarboxylative Minisci reactions are limited to aliphatic carboxylic acids, as their analogs, silanecarboxylic acids, have been rarely investigated. Herein, we present a new decarboxylative Minisci-type reaction of N-heteroarenes with silanecarboxylic acids under photo- or silver-mediated conditions. This C-H silylation strategy provides efficient access to diverse N-heteroarylsilanes in moderate to excellent yields with high regioselectivity, among which Ag-catalysed decarboxylation of silanecarboxylic acids furnishes an unprecedented method for silyl radical generation.

Copper-Mediated Decarboxylative Coupling of 3-Indoleacetic Acids with Pyrazolones

A copper-mediated decarboxylative coupling reaction of 3-indoleacetic acids with pyrazolones was described. This protocol realized new functionalization of pyrazolones under simple reaction conditions and exhibited high functional group compatibility and broad substrate scope. Notably, the products displayed antiproliferative activity against cancer cells.

Exploring Eosin Y as a bimodular catalyst: organophotoacid mediated Minisci-type acylation of N-heteroarenes

Here we report Eosin Y as a bimodular catalyst for Minisci-type acylation reactions. The formation of organic exciplexes between photoexcited Eosin Y and N-heteroarenes was found to be a stabilizing factor for photoacid catalysis under optimized conditions. Spectroscopic investigations such as steady state fluorescence quenching and dynamic lifetime quenching experiments were employed to better understand the role of Eosin Y as both a photoredox catalyst and a photoacid. Feedstock aldehydes were employed as acyl radical precursors for engaging in C-C bond formation reactions with a variety of nitrogen containing heterocycles.

Photo-redox catalyzed dehydrazinative acylation of N-heterocycles via Minisci reaction

Visible light-induced acylation of heteroaromatic compounds have been achieved using benzoyl hydrazides as an efficient acyl source under mild reaction conditions. The photo-redox catalyzed oxidative cleavage of hydrazides leads to in situ formation of acyl radicals, which subsequently couple with various N-heterocycles to produce acylated products. This synthetic strategy performs the classic Minisci reaction in an eco-friendly and greener way with functional group tolerance and regioselectivity. Control experiments confirm the radical pathway for this transformation.

Visible light-induced acylation of heteroaromatic compounds have been achieved using benzoyl hydrazides as an efficient acyl source under mild reaction conditions.

Minisci aroylation of N-heterocycles using choline persulfate in water under mild conditions

A modified Minisci aroylation of isoquinoline using arylglyoxylic acids in the presence of choline persulfate or pre-composition (choline acetate and K2S2O8) in water at ambient temperature affording aroylated isoquinolines is reported.