Rapid CO2 coupling to propargylic alcohols: unlocking the production of α-alkylidene cyclic carbonates via continuous flow

Abstract

α-Alkylidene cyclic carbonates (αCCs) are gaining interest as building blocks in organic and polymer chemistry. To date, their synthesis via the coupling of CO₂ to propargylic alcohols has been restricted to batch processes, with extensive efforts devoted to improving catalytic systems. Herein, utilizing a refined, homogeneous silver–carbene–organobase catalytic system, we optimized batch conditions to achieve, for the first time, complete conversion of tertiary propargylic alcohols within minutes instead of hours. Building on this, we introduce a continuous flow methodology to produce a library of αCCs, achieving the highest space–time yields reported, with quantitative conversions in less than 20 minutes and outputs up to 111 grams per day. This approach reduces CO₂ usage to 1 or 2 equivalents, improves parameter control, and is expected to facilitate scalability. In addition, “plug-and-play” lab-scale continuous flow modules enable seamless integration of subsequent αCC transformations without intermediate purification, as illustrated by the aminolysis of αCCs into oxazolidones with good conversion (91%). Furthermore, supporting the silver–carbene catalyst on a polymer matrix eliminates silver contamination and even suppresses the need for a base co-catalyst. This work advances the scalable synthesis of αCCs via continuous flow, marking a significant step toward greener, CO₂-based cyclic carbonates and derivatives.