Zinc-Catalyzed Reduction of Amides: Unprecedented Selectivity and Functional Group Tolerance

摘要

The catalytic reduction of amides to amines under mild conditionsnconstitutes a highly desired transformation for organic synthesisnand the pharmaceutical as well as agrochemical industry.n1nIn thisnrespect, high selectivity and broad tolerance toward functionalngroups are key factors for the acceptance and application of a givennmethodology. Most of the known reductive transformations ofnamides to amines make use of stoichiometric amounts of traditionalnaluminum and boron hydrides.n2,3nIn spite of their utility, clearndrawbacks of these reagents are air and moisture sensitivity as wellnas the resulting costly purification of the products and concomitantnformation of environmentally hazardous waste materials. Due tonthese problems, the development of catalytic reductions of amidesnis of high actual interest.n4nUnfortunately, the direct hydrogenationnis still in its infancy.n5nOn the other hand, the catalytic hydrosilylationnof carboxamides applying precious metal catalysts like Rh,n6a cnRu,n6c gnPt,n6c,hnPd,n6cnIr,n6cnand othersn6c,i knhas been more intensivelyninvestigated. Most recently, also Fe-based catalysts have beennsuccessfully applied for this purpose at higher temperature.n6l,mnNevertheless, until today a general methodology for the reductionnof amides under mild conditions with inexpensive and environ-nmentally friendly catalysts is not available.