Palladium-Catalyzed Ligand-Free Decarboxylative Coupling of α- Oxocarboxylic Acid with Aryl Diazonium Tetrafluoroborate: An Access to Unsymmetrical Diaryl Ketones

Abstract

Diaryl ketones are of much importance in organic synthesis as versatile intermediates and in industry for their useful properties. A mild and efficient palladium-catalyzed traditional ligand-free decarboxylative coupling of aryl α-keto carboxylic acid with aryl diazonium fluoroborate has been developed. A series of unsymmetrical diaryl ketones has been synthesized in moderate to good yields using this procedure. A radical pathway involving the acyl radical has been suggested.

Recent Progress in Palladium‐Catalyzed Radical Reactions

“…developed a palladium‐catalyzed decarboxylative coupling reaction of α‐keto carboxylic acids 271 with aryl diazonium fluoroborate 272 .Various unsymmetrical diaryl ketones 273 were obtained in moderate to excellent yields without traditional ligand (Scheme 75). [57] Aryl diazonium fluoroborates bearing electron‐donating or electron‐withdrawing groups were well tolerated in this reaction. Moreover, various aryl glyoxylic acids and aryl diazonium fluoroborates exhibited quite good functional group tolerance in the reaction, such as halogen, methyl and methoxy.…”

Recent Development of Aryl Diazonium Chemistry for the Derivatization of Aromatic Compounds

“…Another type of Pd-catalyzed coupling reaction involves the oxidative decarboxylative coupling of aryl α-keto carboxylic acid 156 with aryl diazonium fluoroborates, which represents a complementary synthetic route to the carbonylation reactions (Scheme 116). 231 Both radical trapping experiments and EPR spectroscopy results indicate that this protocol proceeds through a single-electron oxidation pathway involving the formation of an acyl radical.…”

Carbonylative Suzuki–Miyaura couplings of sterically hindered aryl halides: synthesis of 2-aroylbenzoate derivatives

“…Attempts to increase the yield by slow addition of the DABO boronate 6 or the trihydroxyborate 7 were not successful due to low solubility of these boronic acid derivatives in the reaction medium (toluene/water). The use of other solvent systems dramatically reduced the yields (Table ESI- [16][17][18][19]). The best system using PEPPSI-IPr (3 mol%) as catalyst precursor, Cs 2 CO 3 as base in chlorobenzene or anisole as solvent provided the product 2aa in 63% yield ( Table 1 and Table ESI-6, entry 16).…”

“…On the other hand, the biaryl ketone subscaffold of 2aroylbenzoic acids has been synthesized by transition metalcatalyzed carbonylative cross-couplings of organometallic reagents and aryl electrophiles, [13][14][15] or the non-decarbonylative coupling of acyl electrophiles, e.g. carboxylic acids, [16][17][18] esters [19][20][21] or amides. 19,22 Despite the advances in the synthesis of biaryl ketones, only few methods have been demonstrated to be applicable for the formation of 2-aroyl benzoic acid derivatives.…”