Robust Silver(I) Catalyst for the Carboxylative Cyclization of Propargylic Alcohols with Carbon Dioxide under Ambient Conditions

Abstract

Inspired by the bulkier bis(triphenylphosphine)–silver cation‐induced mechanism of propargylic alcohols and carbon dioxide through the alkyl carbonate intermediate, a robust dual‐component catalytic system consisting of silver acetate and tetraheptylammonium bromide was rationally developed for the synthesis of α‐methylene cyclic carbonates under ambient conditions without employing any additional organic base and ligand. This is one of the most effective catalysts reported to date for this conversion, with a very high turnover number of up to 6024, probably due to the synergistic effect of Lewis basic and Lewis acidic species for the activation of both propargylic alcohol and carbon dioxide by the formation of the alkyl carbonate with a bulkier counterion. Notably, this catalyst also worked well for the carboxylative cyclization of propargylic amines with carbon dioxide with the highest turnover number of 544.magnified image

Ag(I)/(C2H5)4NCl Cooperation Catalysis for Fixing CO2 or Its Derivatives into β‐Oxopropylcarbamates

“…The result gained from (C 2 H 5 ) 4 NCl was better than the others. In the previous report, AgOAc/( n C 7 H 15 ) 4 NBr system was demonstrated to be effective in the carboxylative cyclization of propargylic alcohol and CO 2 . Therefore, the catalytic system i. e. AgOAc/( n C 7 H 15 ) 4 NBr was also examined as comparison (entry 12).…”

“…To our delight, the catalytic ability was greatly enhanced upon the addition of quaternary ammonium salts (entries 7–11). It was most likely ascribed to that the quaternary ammonium salts with steric cation had the ability to enhance the nucleophilicity of the reaction intermediate . Herein, several silver compounds were carefully screened in conjunction with (C 2 H 5 ) 4 NCl, and the catalytic performance was significantly improved, indicating the synergistic effect of silver(I) and quaternary ammonium salt catalyst in the transformation.…”

“…Generally, tertiary alcohols are more active than primary alcohols and secondary alcohols and meanwhile showed distinct reactivity with different substituent groups. Deduced from previous study, propargylic carbonate intermediate was easily generated through the reaction of tertiary alcohols and CO 2 with the assistance of suitable catalysts . Propargylic alcohols with cycloalkyl substitution ( 1 e ) performed relatively lower reactivity (entry 5), and the reason could be the steric hindrance effect on the formation of carbonate intermediate.…”

Boosting the Catalytic Performance of Organic Salts for the Fast and Selective Synthesis of α‐Alkylidene Cyclic Carbonates from Carbon Dioxide and Propargylic Alcohols

“…The few examples of the organocatalysed coupling reactions promoted at low CO 2 pressure (1 bar) were performed with a large excess of the catalyst compared to the reactant . New trends deal with the development of binary catalysts that combine metal species with ILs or organic bases . These catalysts work by the synergistic activation of both the substrate and CO 2 or by the double activation of the substrate through the hydroxyl and alkyne groups.…”

“…However, a high catalyst loading (20 mol %) was required, and the co‐catalyst was used in an equimolar amount with respect to the propargylic alcohol. AgOAc/tetraalkylammonium bromide salt, AgOAc/Schiff base ligands, AgI/AcO − catalysts and AgOAc/DBU have also been described as catalytic systems. Although some of them were very active for the selective formation of αCCs, one of the components of the binary catalyst, generally the base, was used in an equimolar amount or even in excess with respect to the propargylic alcohol.…”