Syntheses of Bridged Fenestranes via Stepwise Intramolecular Diels–Alder Reaction and Nitrone Cycloaddition and Their Structural Analyses

Fenestranes contain four rings sharing one carbon atom and have garnered considerable attention because of their physicochemical properties. We synthesized bridged fenestranes with an unsymmetrical skeleton via stepwise cycloadditions including intramolecular Diels-Alder reaction and nitrone cycloaddition. A total of ten fenestranes were synthesized, and the obtained framework was modified to access different derivatives. X-ray crystallography analysis and DFT calculations of the fenestranes revealed that the central carbon was sufficiently flattened even when the fenestrane skeleton was partially cleaved.