Synthesis of 1,2-Fused/Disubstituted Benzimidazoles and Benzimidazolium Salts by I2-Mediated sp3 C-H Amination.

An intramolecular sp3 C-H amination reaction of aniline derivatives has been established. This reaction employs molecular iodine (I2) under transition-metal-free conditions and produces 1,2-fused or 1,2-disubstituted benzimidazoles. This operationally simple synthetic process works well with N-substituted aniline substrates, forming novel benzimidazolium frameworks. Under the optimal reaction conditions, a broad variety of 1,2-fused/disubstituted benzimidazoles and benzimidazolium salts, including several bioactive compounds, were synthesized from readily accessible precursors in an efficient and scalable fashion.

Synthesis of 1,4-Dihydropyridines and Related Heterocycles by Iodine-Mediated Annulation Reactions of N-Cyclopropyl Enamines.

The annulation of N-cyclopropyl enamines to produce 1,4-dihydropyridine (1,4-DHP) derivatives is described. In the presence of molecular iodine (I2), an N-cyclopropyl enamine substrate undergoes iodination, opening of the cyclopropyl ring, and annulation with a second molecule of the substrate to form the 1,4-DHP product. This reaction is amenable to gram-scale operations under mild reaction conditions with no transition metals being required. Further transformations of the 1,4-DHPs leads to related pyridine and bicyclic frameworks.