Selective Reductions: II. The Reaction of Lithium Tri‐ t ‐Butoxyaluminohydride with Selected Organic Compounds Containing Representative Functional Groups

A systematic study was made of the rates and stoichiometry of the reaction of lithium tri‐ t ‐butoxyaluminohydride in tetrahydrofuran solution at 0° with selected organic compounds containing representative functional groups in order to establish the utility of the reagent as a selective reducing agent. Aldehydes and ketones are rapidly reduced, with no complications introduced by the presence of a conjugated double bond, as in cinnamaldehyde. Epoxides are reduced slowly, with styrene oxide and 1,2‐butylene oxide yielding the secondary alcohol exclusively. Acid chlorides and acid anhydrides are rapidly reduced with the up‐take of two moles of hydride per mole of organic reactant. Esters and lactones react more slowly, and no reduction occurs with carboxylic acids under these conditions. Of the nitrogen derivatives examined, phenyl isocyanate undergoes reaction, nitropropane and pyridine oxide are slowly reduced, whereas no reduction is observed for amides, nitriles, oximes, nitrobenzene, azobenzene, azoxybenzene and pyridine. Finally, disulfides are reduced at a moderate rate and cyclohexyl tosylate at a slow rate but sulfoxides, sulfones and sulfonic acids are not attacked by the reagent. Hydroxylic compounds react to liberate hydrogen. However, the yield of hydrogen is usually diminished by a competing reaction in which the hydroxylic compound displaces t ‐butyl alcohol from the reagent, the latter failing to liberate hydrogen under these conditions.