Direct Synthesis of N-Monosubstituted Benzimidazol-2-ones via Ph P-I -Mediated Reaction of Hydroxamic Acids

A facile approach for the synthesis of benzimidazolones via a Ph3P?I2 promoted reaction of hydroxamic acids is reported. Upon Lossen-type rearrangement of the O-activated hydroxamic acids, the in situ generated isocyanates undergo an intramolecular attack by ortho N-nucleophiles producing the cyclized products in good yields under mild conditions. The method allows the direct preparation of a single regioisomer of N-monosubstituted derivatives using readily accessible starting materials and low-cost reagents with broad substrate scope.