Rh(III)-Catalyzed Oxidative [5 + 2] Annulation Using Two Transient Assisting Groups: Stereospecific Assembly of 3-Alkenylated Benzoxepine Framework.

A unique Rh(III)-catalyzed oxidative [5 + 2] annulation of easily available 2-alkenylphenols with propargyl carbonates have been developed by using two O-containing functional groups as the traceless assisting groups (AGs). The experimental investigations together with the density functional theory (DFT) calculations revealed that this transformation involves the free OH-directed cleavage of one terminal C-H bond of the alkenyl moiety and regioselective alkyne insertion, followed by OBoc-promoted intramolecular nucleophilic substitution and β-H elimination that used an allyl species as the active intermediate, giving direct access to the 3-alkenylated benzoxepine skeleton with broad substrate compatibility and good functional group tolerance.