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.