Cu‐Catalyzed Chemoselective Reduction of N‐Heteroaromatics with NH3 · BH3 in Aqueous Solution

Main observation and conclusion An efficient catalytic system was successfully developed on reduction of N‐heteroaromatics with H3N∙BH3 as hydrogen source in CuSO4 solution, featuring excellent chemoselectivity as well as very broad functional group tolerance. Various challenging substrates, such as OH‐, NH2‐, Cl‐, Br‐, etc., contained quinolines, quinoxalines, 1,5‐naphthyridines and quinazolines were all reduced smoothly. Mechanistic studies suggested that [Cu‐H] intermediate might be generated from NH3∙BH3, which was believed to form with H3N∙BH3 in CuSO4 solution.