A Safer Reduction of Carboxylic Acids with Titanium Catalysis

Ammonia-borane, shown previously to react with carboxylic acids under reflux to form primary amides, reduces acids to alcohols at room temperature in the presence of catalytic TiCl₄. The process, which is tolerant of a variety of potentially reactive functional groups, including N-protected amino acids, can be employed for the selective reduction of acids in the presence of amides, nitriles and, to some extent, esters. Aliphatic acids can be selectively reduced in the presence of aromatic acids.