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

An efficient base-promoted C(sp)-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 4 H-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(sp)-H bond functionalization and that this reaction could have occurred through tandem C-O bond cleavage/Michael addition/annulation reactions.