Intramolecular 4+3 cycloadditions. A cyclohexenyl cation, its halogenated congener and a quasi-Favorskii rearrangement

Treatment of alkoxycyclohexenols bearing a tethered diene substituent with a Lewis acid results in intramolecular 4+3 cycloaddition with complete endo selectivity. A cycloadduct bearing a bromo substituent at a bridgehead position undergoes a quasi-Favorskii rearrangement in near quantitative yield upon reaction with lithium aluminum hydride.