A new type of minor enantiomer recycling has been developed and used for the synthesis of enantioenriched cyanoformate esters. The reaction between benzaldehyde and methyl cyanoformate in a two-phase system consisting of toluene and buffer is catalyzed by a chiral Lewis acid, (S,S)-Ti salen dimer 1 , and gives a high yield but a moderate ee at room temperature. Selective recycling of the minor enantiomer to the starting aldehyde and methyl carbonate is catalyzed by an enzyme, Porcine pancreas lipase (2 ). By continuous addition of methyl cyanoformate, recycled aldehyde can react repeatedly until both high yield and high enantiomeric excess are obtained.In order to allow the cyclic process, a thermodynamic driving force for the reaction, such as the evolution of CO2, is crucial. The evolution of CO2 from methyl carbonate is, however, not spontaneous under current conditions but it can be catalyzed by a second enzyme, bovine carbonic anhydrase (3 ).

Minor enantiomer recycling - CO<sub>2 </sub>formation as the driving force

248th National Meeting (2014)

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Minor enantiomer recycling - CO2 formation as the driving force

Minor enantiomer recycling - CO₂formation as the driving force