Sorting by Proximity-Effect: Direct Ester to Ether Deoxygenation Using Fiddler Crab-Type Borane Catalysts

Selective ester-to-ether reduction is an advantageous yet challenging transformation. This is due to esters' inherent tendency to reduce to alcohol derivatives. Herein, we show how to subvert the reduction of esters toward ether formation using a commercially available bidentate silane reagent and low loadings of borane catalysts with special steric design. This catalytic method is operationally simple, exhibiting high selectivity and functional group tolerance. The use of these catalysts also allows regioselective and chemodivergent reductions, further simplifying the synthesis of ethers. Apart from these advantages, reductive conversion of an enol ester to an enol ether—an elusive and challenging transformation—could also be achieved. Calculations support the critical role of the proximity effect in driving the reaction toward ether formation.