Palladium-Catalyzed Decarboxylative Cross-Coupling Reactions: A Route for Regioselective Functionalization of Coumarins

Abstract

A straightforward, regioselective, and step-economical ligand-free palladium-catalyzed decarboxylative functionalization of coumarin-3-carboxylic acids is devised. This protocol is compatible with a wide variety of electron-donating and -withdrawing substituents and allows for construction of various biologically important π-electron extended coumarins.

Decarboxylative Coupling Techniques

“…In 2013, Jafarpour and coworkers [22] reported a versatile, regioselective, and step-economical decarboxylative arylation of coumarin-3-carboxylic acids via a ligand-free palladium-catalytic system (Scheme 3.10). This protocol was compatible with a wide variety of electron-donating and electronwithdrawing substituents, and allowed the construction of several biologically important π-electronextended coumarins.…”

“…A vial equipped with a stir bar is charged with coumarin-3-carboxylic acid (0.25 mmol), 1-iodo-4methoxybenzene (0.33 mmol), PdCl 2 (5 mol%), and Ag 2 CO 3 (0.75 mmol) [22]. Dry degassed DMSO (3 ml) is then added, and the vial is capped.…”

“…Scheme 3.10 Palladium-catalyzed decarboxylative arylation of coumarin-3-carboxylic acids with aryl iodides, as described by Jafarpour and coworkers[22].…”

Microwave-Assisted Silver-Catalyzed Protodecarboxylation and Decarboxylative Iodination of Aromatic Carboxylic Acids

“…Decarboxylative cross-coupling reaction starts with the formation of metal carboxylates from carboxylic acid substrate and metal catalyst, the pivotal step of CO 2 extrusion from the metal salts of carboxylates typically proceeds under rather forcing reaction conditions. Over the years, various metal catalytic systems-both monometallic and bimetallic-have been discovered and developed to turn this strategy applicable for organic synthesis [4,7].…”

Highly Regioselective α‐Arylation of Coumarins via Palladium‐Catalyzed CH Activation/Desulfitative Coupling

“…[9] a-Functionalization of unsaturated carbonyl compounds is a desirable but challenging strategy due to the requisite for prefunctionalizations at the a-position (Scheme 1, path b). [12] To the best of our knowledge, despite the importance of direct a-arylation of a,b-unsaturated carbonyl compounds via C À H activation process only rare examples are reported which usually suffer from low functional group tolerance, low yields of adducts and harsh reaction conditions. [11] Very recently, we also reported a palladium-catalyzed decarboxylative arylation of coumarin-3-carboxylic acids using iodoarenes where the carboxylate group warranted regioselective arylation at C-3.…”