Catalytic Coupling of Carbon Dioxide with Terpene Scaffolds: Access to Challenging Bio-Based Organic Carbonates

The challenging coupling of highly substituted terpene oxides and carbon dioxide into bio‐based cyclic organic carbonates catalyzed by Al(aminotriphenolate) complexes is reported. Both acyclic as well as cyclic terpene oxides were used as coupling partners, showing distinct reactivity/selectivity behavior. Whereas cyclic terpene oxides showed excellent chemoselectivity towards the organic carbonate product, acyclic substrates exhibited poorer selectivities owing to concomitant epoxide rearrangement reactions and the formation of undesired oligo/polyether side products. Considering the challenging nature of these coupling reactions, the isolated yields of the targeted bio‐carbonates are reasonable and in most cases in the range 50–60 %. The first crystal structures of tri‐substituted terpene based cyclic carbonates are reported and their stereoconnectivity suggests that their formation proceeds through a double inversion pathway. Bioconversions! A general catalytic method for the coupling between terpene oxides and CO2 has been developed furnishing bicyclic and acyclic bio‐carbonates in appreciable yields. The chemoselectivity features of both types of carbonate syntheses were studied in detail and the first crystallographic analyses of such terpene carbonate scaffolds are presented. The results pave the way for the use of terpenes as synthons towards new materials and fine chemicals.