Regiocontrolled Synthesis of 1-Substituted-3(5)-carboxyalkyl-1H-pyrazoles Using Trichloromethyl Enones

Photo-on-Demand In Situ One-Pot Synthesis of Carbonate Esters from Tetrachloroethylene

The present study reports a novel one-pot synthesis of carbonate esters with photo-oxidized tetrachloroethylene (TCE). Acyclic and cyclic alkyl carbonate esters could be synthesized through base-promoted condensation reactions of alcohols with the photo-oxidized TCE that was prepared by irradiation with UV-C or visible light under O2 or O2/Cl2 (∼4%) bubbling, respectively. Cyclic carbonate esters could also be synthesized from a solution of TCE and the ethylene glycol derivative by irradiation of UV-C light under O2 bubbling. With respect to the reaction mechanism, the photochemical oxidation of TCE mainly provides the highly toxic and corrosive trichloroacetyl chloride (TCAC), which then reacts in situ with the alcohol to give the corresponding trichloroacetic acid ester (TCAE). The subsequent intermolecular or intramolecular base-catalyzed condensation reaction of TCAE with or without the addition of alcohol leads to elimination of CHCl3 in the corresponding carbonate ester. The present reactions enable the in situ one-pot synthesis of a variety of alkyl carbonate esters under mild conditions without the direct handling of TCAC. This is beneficial in terms of safety, cost, and reduced environmental impact.