Synthesis of Bridged Bicyclic Lactones of Dihydroheteroaromatics

Significance

The reactions of diverse pyridine and quinoline derivatives with bis(trimethylsilyl)ketene acetals in the presence of stoichiometric amounts of methyl chloroformate to afford corresponding 2- and 4-substituted dihydro systems is described. The derived products, obtained in good to excellent yields, are efficiently converted into bridged bicyclic γ- and δ-lactones by electrophile (H⁺, Br⁺, I⁺, OH⁺) induced intramolecular ring-closing reactions. The structures of some of the new heterocycles were assigned by X-ray crystal structure analysis. The analogous reactions for pyrazines and isoquinolines are also reported.