Selective Reductions. 39. Partial Reduction of Carboxylic Acids with Thexylchloroborane-Methyl Sulfide. A Direct and Simple Aldehyde Synthesis

摘要

A systematic study of the direct partial reduction of carboxylic acids to the corresponding aldehydes with thexychloroborane-methyl sulfide (ThxBHCI-SMe2) under practical conditions (methylene chloride, room temperature) has been carried out. The reaction is quite general, and the yields of aldehydes are very good, almost quantitative in the aliphatic series. Many other readily reducible functional groups tolerate these reaction conditions. Furthermore, aliphatic carboxyl acids can be reduced selectively in the presence of aromatic acids. The aldehyde products are readily isolated in high yields either by forming the sodium bisulfite adduct, followed by regeneration with formaldehyde, or by using steam distillation to remove the byproduct.