Silver‐catalyzed Double Decarboxylative Radical Alkynylation/Annulation of Arylpropiolic Acids with α‐keto Acids: Access to Ynones and Flavones under Mild Conditions

Abstract

Ynones are privileged building blocks in various organic syntheses of heterocyclic derivatives due to their multifunctional nature, and flavones are an important class of natural products with a wide range of biological activities. We describe the catalytic double decarboxylative alkynylation of arylpropiolic acids with a-keto acids. With Ag(I)/persulfate as the catalysis system, the valuable ynones bearing various substituents could be easily obtained. The introduction of hydroxyl substituent on ortho-site of a-keto acids make this strategy further applicable to the construction of flavone derivatives via heteroannulation in moderate to good yields with a similar silver-catalyzed system. The reactions proceed under relatively mild reaction conditions and tolerate a wide variety of functional groups. Control experiments indicated that both the reactions undergo radical processes.

Alkynylation of radicals: spotlight on the “Third Way” to transfer triple bonds

“…A classical addition–elimination mechanism was proposed for this reaction. Using similar reaction conditions developed by Li,34 Qi and coworkers reported a double decarboxylative radical alkynylation of arylpropiolic acids with α-ketoacids to access ynones 35…”

Metal-Promoted Heterocyclization: A Heterosynthetic Approach to Face a Pandemic Crisis

“…The potential of a metal-promoted decarboxylative coupling/annulation protocol was exploited by Qi and coworkers. They utilized Ag(I) salt to trigger radical tandem alkynylation/annulation to yield a plethora of flavones 99 in mild conditions, identifying arylpropiolic acids 95 and α-keto acids 98 as valid precursors for the reaction ( Scheme 41 ) [ 102 ].…”

“…The potential of a metal-promoted decarboxylative coupling/annulation protocol was exploited by Qi and coworkers. They utilized Ag(I) salt to trigger radical tandem alkynylation/annulation to yield a plethora of flavones 99 in mild conditions, identifying arylpropiolic acids 95 and α-keto acids 98 as valid precursors for the reaction (Scheme 41) [102]. This simple and selective one-pot metal-catalyzed synthetic methodology leads to the formation of a large array of homoisoflavonoids 97 and flavones 96 in good yields, starting from cheap salicylaldehyde and easily accessible propiolic acid.…”

Acyl Radical Chemistry via Visible-Light Photoredox Catalysis

“…α-Hydroxy or α-amino ketones RC(O)–X [X = CH(OH)R or CH(NH 2 )R] 8a, 8b, 9 or cyclic ketones (via a Norrish type I cleavage) 10 or esters (via the photo-Fries rearrangements) 11 or acyl-cobalt salophen reagents [X = Co(salophen)Py] 12 can all also deliver acyl radicals (method C). In addition, peroxide-mediated homolytic abstraction of a hydrogen atom from aldehydes and α-keto acids are the viable option for the generation of an acyl radical 13 (method D). Many directed or non-directed C-H acylation processes catalyzed by transition-metals were developed in the last decades using this strategy.…”