Palladium-Catalyzed C-H Functionalization of Amido-Substitued 1,4-Napthoquinone in the Presence of Amines toward the Formation of Pyrroles and Imidazoles

Abstract

Transition metal-catalyzed ortho- C−H functionalization of amido-substituted 1,4-naphthoquinone, 3, in the presence of Pd(OAc)2 and tertiary amines led to the formations of 4 with newly generated pyrrole rings. Similar reactions were carried out with primary amines and yielded 5, having imidazole rings, as well as amination products 6. In the cases of reacting with secondary amines, the route for the formations of 4-like, rather than 5-type, products were prevailed. As revealed from the crystal structures of 4_Bu, 6_Bu, 6_Cy, and 4_Cy, cyclization processes indeed took place to form pyrrole and imidazole rings, respectively, which are fused to the former naphthoquinone framework. The crystal structure of 5_Cy shows that it is a product from amination reaction. Similar reaction was carried out using PCy3 as the phosphine source and an unexpected product 7 was obtained. The crystal structure of 7 exhibits that the moiety of PCy3 attaches to the framework of the former naphthoquinone and brings about a new P=C double bond. In addition, the amide fragment of 3 is hydrolyzed and reduced and forms C=N double bond. Here, distinct reactivity of amines from that of phosphines in this type of reactions have been manifested.