CO2-Enabled Cyanohydrin Synthesis and Facile Iterative Homologation Reactions**

Thermodynamic and kinetic control of a chemical process is the key to access desired products and states. Changes are made when a desired product is not accessible; one may manipulate the reaction with additional reagents, catalysts and/or protecting groups. Here we report the use of carbon dioxide to accelerate cyanohydrin synthesis under neutral conditions with an insoluble cyanide source (KCN) without generating toxic HCN. Under inert atmosphere, the reaction is essentially not operative due to the unfavored equilibrium. The utility of CO2-mediated selective cyanohydrin synthesis was further showcased by broadening Kiliani-Fischer synthesis under neutral conditions. This protocol offers an easy access to a variety of polyols, cyanohydrins, linear alkylnitriles, by simply starting from alkyl- and arylaldehydes, KCN and an atmospheric pressure of CO2.

Automated summary

Thermodynamic and kinetic control of a chemical process is crucial for accessing desired products, and using carbon dioxide to accelerate cyanohydrin synthesis under neutral conditions has shown broad utility. This method offers a simple pathway to obtain a variety of polyols and showcases the importance of controlling chemical reactions for desired outcomes.