Selective Reduction of Esters to Aldehydes Using Fiddler Crab-Type Boranes

The partial reduction of esters to aldehydes is a fundamentally important transformation for the synthesis of numerous fine chemicals and consumer goods. However, despite the many efforts, limitations have persisted, such as competing overreduction, low reproducibility, use of exigent reaction conditions and hazardous chemicals. Here, we report a novel catalyst family with a unique steric design which promotes the catalytic partial reduction of esters with unprecedented, near-perfect selectivity and efficiency. This metal-free catalytic method is ready to be placed at the disposal of chemists to provide valuable aldehyde intermediates and products and shows promise for streamlining synthetic methods in academic and industrial settings.