Tandem annulation and dipolar cycloaddition of azomethine imines in catalytic C(sp²)–H functionalization

The synthesis and functionalization of privileged nitrogen heterocycles has emerged as a central topic in drug discovery and material science. In this context, the tandem C–H functionalization and intramolecular annulation has received prodigious attention, as it is able to expedite the construction of heteroaromatic frameworks beyond conventional C–H functionalization. In general, significant effort has been made to develop the [3 + 2] dipolar cycloaddition of azomethine imines with π-unsaturated compounds. Moreover, the [3 + 3], [4 + 3], [3 + 2 + 2], and [5 + 3] cycloaddition reactions of azomethine imines with various dipolarophiles have been demonstrated. To date, however, the combination of catalytic C–H functionalization and intramolecular cyclization using azomethine imines as both directing groups and dipolar units has been less explored. This review focuses on recent progress toward the catalytic tandem C–H functionalization and dipolar cycloaddition of azomethines imines with a range of coupling partners.