Aromatic C–H Bond Functionalized via Zwitterion Intermediates to Construct Bioxindole Containing Continuous Quaternary Carbons

Both bioxindoles and continuous quaternary carbons play important roles in pharmaceutical scaffolds. However, few examples were developed to construct bioxindoles containing continuous quaternary carbons because of the steric hindrance effect. Here, a rhodium­(II)-catalyzed three-component reaction of N,N-disubstituted anilines, 3-diazooxindoles, and isatin ketimines to deliver the 3-amino-3′-aryl-bioxindole compounds containing continuous quaternary carbons as products is developed. This transformation is proposed to proceed in a Mannich-type trapping of a zwitterion intermediate initiated from aromatic C–H bond functionalization. Several of these compounds exhibit good inhibitory activity against growth of osteosarcoma cell lines.