C(sp3)–H Bond Functionalization of Benzo[c]oxepines via C–O bond Cleavage: Formal [3+3] Synthesis of Multisubstituted Chromans

An efficient base-promoted C­(sp3)–H bond functionalization strategy for the synthesis of multisubstituted chromans from the formal [3+3] cycloaddition of benzo­[c]­oxepines and electron-rich phenols has been developed. The corresponding 4H-chromenes can be easily obtained in excellent yields by simple filtration from chromans. Preliminary mechanistic studies indicate that the C–O bond cleavage is the key step for the C­(sp3)–H bond functionalization and that this reaction could have occurred through tandem C–O bond cleavage/Michael addition/annulation reactions.