Nucleophilic‐Bisphosphine‐Catalysed One‐Pot Sequential [4+2]/[4+2] Annulation of an Allenoate with Benzylidenepyrazolones

Abstract

Abstract An efficient bisphosphine‐catalysed sequential [4+2]/[4+2] annulation reaction of a γ‐benzyl allenoate with benzylidenepyrazolones has been developed. Under the catalysis of DPPB [1,3‐bis(diphenylphosphanyl)butane], the [4+2]/[4+2] annulation proceeded smoothly to give spiro‐pyrazolidinone derivatives in moderate yields. This protocol provides a simple and practical strategy for the construction of highly substituted 2 H ‐spiro[naphthalene‐pyrazole] skeletons.