Synthesis of Spiro 3,3'-Cyclopropyl Oxindoles Via N-Bromosuccinimide-Mediated Ring-Closing and Contraction Cascade.

An N-bromosuccinimide-mediated cascade reaction involving the cyclization/oxygen-migration/ring-contraction process of 3-(β, β-diaryl) indolylethanol was disclosed. A variety of spiro 3,3'-cyclopropyl oxindole derivatives were efficiently synthesized in good yields under mild reaction conditions. A possible mechanism was suggested based on intermediate isolation and computational studies.