Rhodium(II)- or Copper(I)-Catalyzed Formal Intramolecular Carbene Insertion into Vinylic C(sp2 )-H Bonds: Access to Substituted 1H-Indenes.

A rhodium(II)- or copper(I)-catalyzed formal intramolecular carbene insertion into vinylic C(sp2 )-H bonds is reported herein. This method provides straightforward access to 1H-indenes with high efficiency and excellent functional-group compatibility. Mechanistically, the reaction is proposed to involve the following sequence: metal carbene formation, intramolecular nucleophilic addition of the double bond to the electron-deficient carbene carbon atom, dearomatization, and finally a 1,5-H shift.