Double Carboxylation Of O-Alkynyl Acetophenone With Carbon Dioxide

Carbon dioxide is the main greenhouse gas, but it is also one of the most important carbon resources. The utilization of carbon dioxide as feedstock in organic synthesis has gained significant attention since it provides the opportunity to convert this greenhouse gas into value-added fine chemicals. In the last decades, various methodologies using carbon dioxide as a carboxylative reagent have been developed, offering an attractive and powerful access to synthetically important carboxylic acids and derivatives. Generally, one single carbon dioxide molecule is incorporated into a product molecule in these carboxylation reactions. Double carboxylation of a substrate using two carbon dioxide molecules is rarely reported.Our previous work revealed that the a-carboxylation of ketones in the presence of suitable base could deliver ?-ketocarboxylate, which conducted a nucleophilic attack towards the silver(I)-activated alkyen moiety to produce a staible product. It's noteworthy that a new metal-carbon bond might be formed during the above cyclization reaction. If the second carbon dioxide molecule could insert into this newly-formed metal-carbon bond, and thus a double carboxylation product would be obtained via a carboxylation/intromolecule cylclization/carboxylation sequence which could pave a'new path for the catalytic transformation of carbon dioxide.Based on the above mechanistic understanding, the reaction of 2-(phenylethynyl)phenylethanone with carbon dioxide was chosen as a model reactant to finally identify the following optimal reaction conditions:10 mol% CuI as catalyst,4 equivalents of cesium carbonate as base, CO2 (2 Mpa) in DMSO at 60? for 24 h, then 5 equivalents of CH3I at 30? for 3 h. Under this condition, a variety of substituted o-alkynyl acetophenone conducted double carboxylation reaction smoothly to give 1(3H)-isobenzofuranylidene dicarboxylic esters in moderate to good yields. The substitute in alkyne moiety has a profound effect on the reaction product and alkyl-substituted substrates show much higher double carboxylation product selectivities than aryl-substituted substrates.