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 H 3 N∙BH 3 as hydrogen source in CuSO 4 solution, featuring excellent chemoselectivity as well as very broad functional group tolerance. Various challenging substrates, such as OH‐, NH 2 ‐, 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 NH 3 ∙BH 3 , which was believed to form with H 3 N∙BH 3 in CuSO 4 solution.