Dual Roles of Methyl Ketones in Radziszewski-Type Reaction: Formal [2 + 1 + 1 + 1] Synthesis of 1,2,5-Trisubstituted Imidazoles.

A highly efficient molecular iodine mediated Radziszewski-type reaction of methyl ketones, anilines, and tosylmethyl isocyanide has been developed. This protocol represents an elegant molecular fragment assembly of imidazoles via a formal [2 + 1 + 1 + 1] annulation. It is the first example where methyl ketones serve as the α-dicarbonyl compounds and aldehydes in Radziszewski-type reactions.