Highly Efficient Synthesis of N-1-Substituted 1H-Indazoles by DBU-Catalyzed Aza-Michael Reaction of Indazole with Enones

摘要

1H-Indazoles are important heterocycles as they are a substantial part in many drugs. Here, a DBU-catalyzed aza-Michael reaction of indazole with enones is described. A variety of aromatic and aliphatic enones are well tolerated and afford the corresponding N-1-substituted 1H-indazoles in high to excellent yields with exclusive N-1-regioselectivity. The use of a metal-free catalyst, good substrate tolerance, mild reaction conditions, and high atom economy make this procedure a direct and facile method for the preparation of N1-substituted 1H-indazoles.