Synthesis of N-acylbenzimidazoles through [4 + 1] annulation of N-arylpivalimidamides with dioxazolones

In this paper, a novel and efficient synthesis of N-acylbenzimidazoles through an unprecedented [4 + 1] annulation of N-arylpivalimidamides with dioxazolones is presented. It is proposed that the formation of the title products should involve a cascade process including Rh(III)-catalyzed C(sp2)–H amidation of N-arylpivalimidamides using a dioxazolone as a masked amidating reagent followed by an intramolecular N-nucleophilic addition and ammonia elimination. To our knowledge, this is the first example in which N-acylbenzimidazoles were synthesized through simultaneous formation of the imidazoyl moiety and introduction of the N-acyl group. Compared with literature methods, this unique protocol has advantages such as easily obtainable substrates, redox neutral conditions, high efficiency, good atom-economy and excellent compatibility with diverse functional groups. With all these merits, it has the potential to find wide applications in related areas.