3D Cyclophane for the Selective Conversion of Epoxide to Cyclic Carbonate.

A novel three-dimensional (3D) cyclophane molecule 1 was synthesized and fully characterized. Cyclophane 1 , which can form a N heterocyclic carbene, was tested for conversion of certain epoxides ( 3 - 6 ) [scheme 2] to cyclic carbonates in the presence of CO 2 . Propylene oxide ( 3 ) was found to have more reactivity with cyclophane 1 compared to the other epoxides. The theoretical calculations based on N,N'-disubstituted imidazol(in)ium-2-carboxylates derived from N,N' disubstituted imidazole as the source of N-heterocyclic carbene show lower activation energy in the case of the reactivity of epoxides 5 and 6 as compared to 3 and 4 . However, cyclophane 1 , which possesses a 3D geometry, can form the open intermediate with CO 2 and propylene oxide more feasibly than the other three epoxides, which have larger sizes as compared to propylene oxide. Hence, the reaction of propylene oxide, CO 2 , and cyclophane 1 can follow the mechanistic path 1, whereas the epoxides 4 - 6 can follow a different mechanistic path 2. Cyclophane 1 is the first example of a cyclophane to act as an organocatalyst for the conversion of CO 2 and epoxide to cyclic carbonate via the N heterocyclic carbene pathway.