Synthesis of Cyclopentadienes for Cyclopentadienyl Ligands via Cp*Rh^III-Catalyzed Formal sp³C-H Activation/Spiroannulations

An efficient Cp*RhIII-catalyzed formal C(sp3)-H activation/spiroannulation of alkylidene Meldrum's acids with alkynes has been developed using catalytical Cu(OAc)2 and air as the oxidant. This reaction demonstrates a new and straightforward approach to spirocyclopentadienes with Meldrum's acid moieties in good to excellent yields under mild reaction conditions with a broad substrate scope. Notably, this protocol provides a novel and straightforward approach to cyclopentadienes with various substitution patterns and the corresponding cyclopentadienyl-type ligands from simple substrates.