Organocatalytic Coupling of CO2 with a Propargylic Alcohol: A Comprehensive Mechanistic Study

Abstract The metal‐free coupling of a propargylic alcohol with CO 2 catalysed by guanidine derivatives was investigated in detail through the combination of online kinetic studies by in situ attenuated‐total reflection IR (ATR–IR) spectroscopy and DFT calculations. Bicyclic guanidines, namely 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) and 7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (MTBD) are effective catalysts for the conversion of 2‐methyl‐3‐butyn‐2‐ol to α‐methylene cyclic carbonate and oxoalkyl acyclic carbonate under mild reaction conditions. The lower selectivity of TBD in comparison with MTBD towards the formation of α‐methylene cyclic carbonate was elucidated from DFT calculations and is related to the bifunctional activity (base/H‐bond donor) of TBD decreasing the Gibbs free energy of the reaction path for the formation of the acyclic carbonate.