Manganese catalyzed chemoselective transfer hydrogenation of unsaturated esters switched by solvent

Abstract

We report a solvent-switchable chemoselective transfer hydrogenation of α,β-unsaturated esters, employing an earthabundant manganese complex as catalyst and ammonia borane as hydrogen donor. Diverse unsaturated esters are efficiently converted to saturated esters in dioxane and primary alcohols in MTBE. Mechanistic investigations demonstrate that manganese hydride species formed in MTBE exhibit superior reactivity to those in dioxane, establishing a practical protocol for this chemoselective reduction. Gram-scale transfer hydrogenation of ethyl cinnamate validates the methodology, affording the saturated ester in 91.2% yield and the primary alcohol in 80% yield under the respective conditions.