METAL-CATALYZED SYNTHESIS OF FIVE-MEMBERED RING N-HETEROCYCLES. A RECENT UPDATE

Abstract

The review deals with the metal-catalyzed synthetic methods used for the construction of 5-membered nitrogen-containing aromatic and nonaromatic heterocycles with one to three nitrogen atoms, published in the years 2008–2017. The methodology is based on the metalcatalyzed activation of the alkyl C(sp³)–H, alkenyl C(sp²)–H, and terminal alkyne C(sp)–H bonds of appropriate precursors in order to perform intermolecular and intramolecular reactions. These bond forming reactions include C(sp³)–C(sp²), C(sp²)–C(sp²), and C(sp²)–C(sp) coupling, hydroamination at C(sp²)–H and C(sp)–H bonds, and oxidative amination of alkyl C(sp³)–H, alkenyl and arene C(sp²)–H, and terminal alkyne C(sp)–H bonds. Two further bond forming methods are intramolecular nitrenoid–arene C(sp²) and cycloaddition reactions. Transition metals are systematically used in these synthetic methods, and only in a few cases Lewis acids are used as catalysts. In general, the metal-catalyzed cyclizations leading to five-membered heterocycles are very efficient and particularly useful in the synthesis of natural and unnatural biologically active products.