Catalyst- and Stoichiometry-Dependent Deoxygenative Reduction of Esters to Ethers or Alcohols with Borane-Ammonia.

A facile and selective room temperature deoxygenation of both aromatic and aliphatic carboxylic esters to ethers has been achieved by regulating the stoichiometry of the reductant, BH 3 -NH 3 , and the catalyst, TiCl 4 . This first, practical borane-mediated process is compatible with various potentially sensitive functional groups and is applicable to the deoxygenative ether formation from typically challenging aromatic acid esters. Substituting BF 3 -Et 2 O as the catalyst alters the reaction pathway, reducing the esters to alcohols. Mechanistic insights are provided by NMR spectroscopy, deuterium labeling, and kinetic isotope studies.