Titanium-Mediated Deoxygenation of Sulfoxides into Sulfides with Ammonia Borane under Mild Conditions

A facile and selective room-temperature deoxygenation of both aromatic and aliphatic sulfoxides to thioethers has been achieved by using a TiCl₄-AB reduction system in good to excellent yields. This first, practical titanium-mediated ammonia borane reduction process is compatible with various potentially sensitive functional groups. The successful execution of a gram-scale reaction confirms the practical utility of this reduction system. Moreover, its effective application to the synthesis and modification of diverse pharmaceutical molecules further demonstrates its versatility. This work also expands the application scope of ammonia borane in the reduction chemistry.