Senior Research Scholar, Indian Institute of Technology Guwahati
Novel polycyclic imidazole were prepared readily from the reaction of 2-hydroxy-C-nitroso compounds
The imidazole core is one of the most common moiety present in a large number of natural products, particularly in bioactive molecules. Various strategies have been developed for the synthesis of imidazole moiety. , , However, the existing methods using metals and oxidants have significant limitations due to involvement of sensitive reaction conditions and production of toxic by-products. We have developed an efficient and simple method for the synthesis of imidazole derivatives via direct C–H functionalization of saturated N-heterocycles without aid of a metallic reagent/catalyst and an external oxidant. A wide range of substituted nitroso-naphthols on reaction with N-heterocycles provided a facile excess to biologically relevant and structurally novel polycyclic imidazoles. Moreover, the same reaction conditions were observed to be effective for the primary amines also. Apart from the nitroso-naphthols, the reaction also proceeded well with other 2-OH-nitroso compounds derived from of Phenanthroline, Dimedone and Coumarin.
Abstract: Hydrogen bond assisted ortho-selective C(sp(2))-H amination of nitrosoarenes and subsequent α-C(sp(3))-H functionalization of aliphatic amines is achieved under metal-free conditions. The annulation of nitrosoarenes and 2-hydroxy-C-nitroso compounds with N-heterocycles provides a facile excess to a wide range of biologically relevant ring-fused benzimidazoles and structurally novel polycyclic imidazoles, respectively. Nucleophilic aromatic hydrogen substitution (SNArH) was found to be preferred over classical SNAr reaction during the C(sp(2))-H amination of halogenated nitrosoarenes.
Pub.: 10 May '17, Pinned: 31 Aug '17