Utilizing Allenic Acids and Heterocyclic Diazo Compounds in the Synthesis of Polysubstituted Spirocyclic Butenolides and β-Methylidene 2-Furanones.

Herein, we report a novel approach for the assembly of spirocyclic Δ α,β -butenolides and β-methylidene 2-furanones via Rh(II)-catalyzed O-H insertion of heterocyclic diazo compounds into allenic acids followed by base-promoted cyclization. Utilizing various diazo heterocycles, including α-diazo homophthalimides, 3-diazo tetramic acids, and diazo oxindoles, diverse spirocyclic scaffolds were produced. The research revealed that the allenic acid substitution pattern is decisive for the product type, enabling extraordinary target compound switching between two types of spirocyclic 2-furanones with exo- and endocyclic C═C bonds.