Radical 5-exo cyclization of alkynoates with 2-oxoacetic acids for synthesis of 3-acylcoumarins

Abstract

A silver-promoted decarboxylative annulation of alkynoates with 2-oxoacetic acids leading to the formation of 3-acyl-4-arylcoumarins is reported. The process involves radical decarboxylative acylation, 5-exo cyclization, and ester migration.

Recent advances in catalytic decarboxylative acylation reactions via a radical process

“…19b Later on, Fu and Shang et al also reported another dual catalytic system merging photoredox with palladium catalysis for this transformation (Scheme 22). 19c Gratifyingly, several functional groups such as halogen, unprotected amine, cyano, 85 ester, acetal, and aldehyde are well tolerated under this mild conditions. Remarkably, the potassium oxalate monoamides are also suitable substrates leading to the corresponding amides in 44-97% yields.…”

“…Furthermore, this protocol could be 80 applied to other heterocyclic compounds such as quinolinones and 1,4-naphthoquinones. 85 …”

“…In this area, we have disclosed a novel Bu 4 NI-catalyzed decarboxylative acyloxylation of a C sp3 -H bond adjacent to a heteroatom (such as N or O). 12a This decarbonylative/dehydrogenative procedure allows an efficient 85 and straightforward access to N-acyloxymethylamides and αacyloxy ethers. It was confirmed that phenylglyoxylic acid can be easily degraded to the corresponding benzoic acid under the TBAI/TBHP system, which could further convert into the desired product.…”

“…Recently, the tandem radical cyclization of N-arylacrylamide with various radical precursors 85 has proven to be one of the most powerful methods for the construction of this skeleton. 5c,d In 2013, we developed a mild and efficient silver-catalyzed tandem decarboxylative radical cyclization of N-arylacrylamides with α-keto acids, which provides a facile route to carbonyl-containing oxindoles 29.…”

Generation of Sulfonyl Radicals from Aryldiazonium Tetrafluoroborates and Sulfur Dioxide: The Synthesis of 3‐Sulfonated Coumarins

“…[17] Interestingly, they found that the reaction proceeded through radical acylation, 5-exo cyclization, and ester migration, which was different from the 6-endo cyclization in previous reports. More recently, Qiu and co-workers reported a silver-promoted acylation of aryl propiolates with 2-oxoacetic acids for the synthesis of 3-acylcoumarins.…”