Selective Organocatalytic Preparation of Trimethylene Carbonate from Oxetane and Carbon Dioxide

The organocatalytic coupling of oxetanes and carbon dioxide (CO2) offers a sustainable route to poly(trimethylene carbonate)s and/or functional six-membered cyclic carbonate monomers. This transformation is more challenging than when using more strained epoxide comonomers and even more so when it is performed using metal-free routes. Herein, we report an organocatalytic oxetane/CO2 coupling procedure that enables the selection of cyclic carbonate or polymer from a common intermediate. Using a novel I2-based binary catalyst system, cyclic carbonate with high selectivity (up to 94%) was obtained at 55 °C, whereas simply changing the temperature to 105 °C yielded the polycarbonate with Mn of up to 6.4 kDa, thus showing that either trimethylene carbonate or its concomitant polycarbonate product can be selected solely by the manipulation of the reaction conditions.