Base-catalyzed Povarov reaction: an unusual [1,3] sigmatropic rearrangement to dihydropyrimidobenzimidazoles.

A novel base-catalyzed Povarov reaction of arylamines, aldehydes, and electron-deficient dienophiles has been developed. An unprecedented in situ [1,3] sigmatropic rearrangement leading to 4,10-dihydropyrimido[1,2-a]benzimidazoles has also been discovered. An insight of the plausible mechanism is discussed and supported by X-ray crystal study. This cascade reaction is achieved in a one-pot multicomponent fashion on soluble support under microwave conditions.