A metal-free dehydrogenative lactonization of 2-arylbenzoic acids at room temperature was developed. This work illustrates the first application of visible-light photoredox catalysis in the preparation of benzo-3,4-coumarins, an important structural motif in bioactive molecules. The combination of photocatalyst [Acr + -Mes] with (NH 4 ) 2 S 2 O 8 as terminal oxidant provides an economical and environmentally benign entry to different substituted benzocoumarins. Preliminary mechanistic studies suggest that this reaction most likely occurs through a homolytic aromatic substitution pathway.

An operationally simple method is disclosed for the decarboxylative cyanation of aliphatic carboxylic acids at room temperature. Riboflavin tetraacetate, an inexpensive organic photocatalyst, promotes the oxidation of carboxylic acids upon visiblelight activation. After decarboxylation, the generated radicals are trapped by TsCN, yielding the desired nitriles without any further additive, in a redox-neutral process. Importantly, this protocol can be adapted to flow conditions.

Abstract:We describe herein a transition-metal-free method for the decarboxylative generation of radicals from carboxylic acids and their 1,4-addition to Michael acceptors. The Fukuzumi catalyst (9-mesitylene-10-methylacridinium perchlorate, [AcrMes]ClO 4 ) enabled this transformation under visible-light irradiation at room temperature with CO 2 as the only byproduct. The scope and limitations of this protocol were examined by using

We report on the use of visible light photoredox catalysis for the radical Smiles rearrangement of 2-aryloxybenzoic acids to obtain aryl salicylates. The method is free of noble metals and operationally simple and the reaction can be run under mild batch or flow conditions. Being a redox neutral process, no stoichiometric oxidants or reductants are needed.

We describe herein a direct decarboxylative allylation of aliphatic carboxylic acids with allylsulfones using visible light and riboflavin tetraacetate (RFTA) as photocatalyst. The reaction proceeds at room temperature tolerating a wide range of functionalities, avoiding the use of external bases or additives. Mechanistic studies support that alkyl radicals are involved in the reaction and that a true photocatalytic cycle is operating. It is proposed that the carboxylic acid is deprotonated by [RFTA]·–, and the corresponding carboxylate acts as a reductive quencher of RFTA*, which after decarboxylation produces the alkyl radical. The methodology was adapted to prepare benzothiazoles substituted at C2, by reacting some carboxylic acids with 2‐(phenylsulfonyl)benzothiazole. The number of carboxylic acids suitable for this arylation was lower than for the allylation and this different reactivity was briefly commented.