Stereoselective Ketal-Tethered Intramolecular Diels−Alder Cycloadditions. An Approach to the 2-Oxadecalin Spiroketal Core of Antifungal Agent Fusidilactone C

[reaction: see text] An approach toward the 2-oxadecalin spiroketal core of fusidilactone C via a rare ketal-tethered intramolecular Diels-Alder cycloaddition is described here. This intramolecular Diels-Alder cycloaddition is highly endo-selective and overall depended upon the nature of solvents and Lewis acids. We also observed some remarkable rate acceleration in MeOH.