Easy Access to Acetal-Spiroacetal-Enol Ethers by Tandem Dearomatization of a Furan Ring and Acetalization

A range of structurally novel acetal-spiroacetal-enol ethers were readily synthesized from 3-[5-(methoxymethyl)-2-furyl]propionaldehydes by dearomatization to form carbocations that were trapped intramolecularly by the formyl group with subsequent acetalization.