A stepwise lactol carbocyclisation to bridged ethers via a keto–acetal cascade

Lactol carbocyclisations provide a succinct method of constructing the oxabicyclo[3.2.1]octane scaffold, motif present in various natural products medicinal interest. Lactols containing an unsaturated ketone or ester were prepared by olefin cross-metathesis; electrophilic alkene derived from methyl vinyl underwent concomitant terminal α-methylenation and oxa-Michael addition to give bridged lactol which then oxygen-to-carbon transposition presence titanium (IV) chloride giving desired carbocyclic seven-membered ether via novel dehydrative cascade considered involve enolates.