A Mild Boc Deprotection Using Armstrong's Acid

Naphthalene-1,5-disulfonic acid, or Armstrong's acid, is demonstrated to be a reliable reagent in the mild deprotection of tert-butyl carbamate (Boc) protecting groups. Our method is operationally simple and affords the deprotected amines as the corresponding disulfonate salts in up to quantitative yields. The reaction is mild and enables efficient deprotection in the presence of other sensitive functional groups. These salts are easily isolable via filtration from the reaction mixture and can be used as is in commonly employed reactions (i.e., reductive amination, amide coupling, Buchwald-Hartwig coupling). Additionally, we disclose the ammonium disulfonate salt as a bench-stable, non-hygroscopic source of ammonia.