Advances in transition-metal catalyzed C–H bond activation of amidines to synthesize aza-heterocycles

Abstract

Amidine compounds, as important nitrogen analogues of isoelectronic carboxylic acids, are found throughout biologically active molecules and serve as the most attractive precursors for the synthesis of N-containing compounds. In this review, the advancements in the synthesis of aza-heterocycles via transition-metal catalyzed C–H bond activation of amidines have been summarized through diverse annulation reactions. Amidines act as two-electron donors via the more basic and less sterically crowded imino lone pair and coordinate with transition-metals, in which N–H imine could act as both directing group and intramolecular nucleophile, electrophile or proton acceptor. The mechanisms of different annulation pathways will be highlighted in this review along with a discussion of more recent developments in the field.