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Sequential C-C σ-Bond Cleavage/(sp2) C-O Bond Formation via C-H Functionalization toward Pyranoindolones Fused with Medium-Sized Rings.

An atom-economical procedure for the synthesis of pyranoindolones fused with 7- or 8-membered rings has been developed. This process is realized through the sequential Cs2CO3-promoted C-C σ-bond cleavage of cyclic ketoesters and a ZnI2-mediated selective C-H/O-H coupling reaction. Two of the C-C σ-bonds are cleaved and one of the sp2 C-H bonds is functionalized during the reaction process. Easily accessible starting materials and broad substrate scope make this protocol attractive in synthetic organic chemistry.