Decarboxylative Giese‐Type Reaction of Carboxylic Acids Promoted by Visible Light: A Sustainable and Photoredox‐Neutral Protocol

• Published in: European journal of organic chemistry 2017-04, Vol.2017 (15), p.2154-2163
• Main Authors: Ramirez, Nieves P., Gonzalez‐Gomez, Jose C.
• Format: Article
• Language: English
• Subjects: Acids; Carbon dioxide; Carboxylic acids; Cascade chemical reactions; Catalysts; Light irradiation; Mesitylene; Photocatalysis; Radical reactions; Sustainability; Sustainable chemistry; Synthetic methods
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201601478

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, [Acr‐Mes]ClO4) enabled this transformation under visible‐light irradiation at room temperature with CO2 as the only byproduct. The scope and limitations of this protocol were examined by using a range of Michael acceptors (15 examples) and carboxylic acids (18 examples). The use of 3‐hydroxypivalic acid in this protocol allowed the straightforward formation of a diastereomerically pure δ‐lactone. Moreover, when a homoallylic acid was used, a radical cascade reaction took place with the formation of three C–C bonds. The decarboxylative alkylation of carboxylic acids can be efficiently promoted by visible light under air at room temperature by using 9‐mesitylene‐10‐methylacridinium perchlorate ([Acr‐Mes]ClO4) as photocatalyst. A range of readily available starting materials are well tolerated in this transition‐metal‐free protocol.