A Theoretical Study on the Mechanism of Bifunctional Brønsted Acid/Base-Catalyzed CO2-Fixation Reaction with Homoallylic Amine.

The reaction mechanism and the enantioselectivity of the Brønsted acid/base (trans-stilbene diamine, simplified by BAM)-catalyzed CO₂ fixation with homoallylic amine have been investigated using density functional theory (DFT) calculations. The proposed mechanism involves the initial activation of the amine by the Brønsted acid, followed by the nucleophilic attack of the amine on CO₂ to form a carbamate intermediate. The Brønsted base subsequently deprotonates the carbamate intermediate to form the cyclic carbamate product, regenerating the Brønsted acid catalyst. The C-O cyclization is the enantio-determining step. The hydrogen bond network formed by the catalyst and substrate, similar to an enzyme pocket, plays a key role in stereoselectivity. In addition, the energy decomposition analysis (EDA) confirms that hydrogen bonding is driven by orbital and electrostatic attractions. The more Brønsted basic BAM catalyst (OMe at the quinoline 7-position) exhibits enhanced enantioselectivity.