Herein, we report
a simple catalytic system consisting of CaI2 in combination
with Et3N as a ligand for the efficient
cycloaddition of CO2 to a variety of epoxides. Terminal
(bio-based) carbonates were obtained under mild conditions (23 °C,
1 bar CO2 pressure) in excellent yields up to 97%. Under
elevated temperature (70 °C) and higher CO2 pressure
(10 bar), even challenging internal epoxides were converted, leading
to the desired carbonates in yields up to 90%. 1H NMR experiments
indicated the in situ coordination of the amine to the Lewis acidic
calcium center as well as the activation of the epoxide. Furthermore,
the enzymatic kinetic resolution of seven cyclic carbonates using
readily available pig liver esterase was investigated. Styrene carbonate
proved to be the most suitable substrate for the kinetic resolution,
leading to (R)-styrene carbonate in 99% ee.
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