Pyrrolidine-Catalyzed Annulations of Quinone Monoacetals with Naphthols: Synthesis of 2-Oxabicyclo[3.3.1]nonane Skeletons, Transformations and Reaction Mechanism

Herein, we report the pyrrolidine-catalyzed annulation reaction of p-quinone monoacetals with naphthols at room temperature. The reaction is also extended to including 4-hydroxycoumarin, 4-hydroxy-1-methylcarbostyril, 4-hydroxycarbostyril, and several β-ketoesters as the nucleophiles, thereby providing a collection of bridged cyclic compounds bearing 2-oxabicyclo[3.3.1]nonane skeletons in 41–96% yields. The reaction can be adapted to gram-scale synthesis, and several transformations of the obtained bridged cyclic products are demonstrated for the preparation of polycyclic compounds that may find utility in related fields. Mechanism studies indicate the engagement of iminium intermediate in the reaction, and a bridged ring enamine intermediate can be observed by NMR. (Figure presented.).