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

Abstract

A novel regioselective a-arylation of coumarins with readily available arenesulfonyl chlorides and sodium arenesulfinates via palladium-catalyzed direct C À H functionalizations under mild reaction conditions is described. This protocol presents an unexpected and highly regio-controlled arylation of coumarins at C-3 to construct interesting 3-arylcoumarins with fascinating biological and fluorescent properties. The regioselectivity observed is in sharp contrast with that expected for the Heck reactions.

Eco‐Friendly Solvents for Palladium‐Catalyzed Desulfitative CH Bond Arylation of Heteroarenes

“…[8] Then, Jafarpour and co-workersd escribed the Pd-catalyzed direct desulfitative arylation of coumarins in the presence of Cu salts in dioxane and the direct desulfitativea rylation of pyrrole in dimethylacetamide (DMA; Figure 1C). [9] Recently,w ed escribed the direct arylation of several heteroarenes, such as (benzo)furans, [10] (benzo)thiophenes, [11] and pyrroles, [12] through ad esulfitative cross-coupling reaction( Figure 1D). Sodium sulfinates have been also used in desulfitatived irect arylations for the arylation of various heteroarenes [13] The reaction proceeded in high yields if 5mol %P dCl 2 (CH 3 CN) 2 was used in the presence of lithium carbonate( Li 2 CO 3 ), sometimes with unexpected regioselectivities.…”

Acylation of Pyrroles and their Free (N‐H)‐Derivatives via Palladium‐Catalyzed Carbopalladation of Nitriles

“…[25] Despite this success with indoles, a similar regioselective direct acylation of pyrroles, which usually suffers from unselectivities and polymerization reactions, is unprecedented. [24] Continuing our efforts in the palladium-catalyzed direct arylation of heterocycles [26] and especially pyrroles, [27] herein we report a straightforward, mild and regioselective direct C-2 acylation of pyrroles and their free (N-H) derivatives with nitriles which, to the best of our knowledge, remains an unsolved problem. This protocol demonstrates new synthetic routes to selectively obtain 2-acylpyrroles under mild conditions and offers highly efficient conditions by minimizing wasteful by-products and precluding N-H protection.…”

Transition Metal Mediated C–H Activation of 2‐Pyrones, 2‐Pyridones, 2‐Coumarins and 2‐Quinolones

“…A palladium-catalysed, regioselective, direct 3-arylation of coumarins with arenesulfonyl chlorides and sodium arenesulfinates was described by Jafarpour (Scheme 52). [59] The authors propose that the first step of the mechanism is oxidative addition of Pd into the S-Cl bond of the arenesulfonyl chloride, followed by extrusion of SO 2 to generate an arylpalladium intermediate (similar to the intermediate generated from traditional oxidative addition into an aryl halide). C-H activation of the 2-coumarin, followed by successive transmetallation with the arylpalladium intermediate and reductive elimination affords the 3-arylated 2-coumarin product.…”