In the presence of boron trifluoride etherate, some kinds of aliphatic ethers have been found to react with benzaldehyde dimethyl acetal yielding alpha,beta-unsaturated carbonyl compounds with evolution of H-2. In this reaction, dehydrogenation of the ether undergoes in cooperation with the acetal and BF3, which enables the ether molecule to behave as enol ether equivalent affording crossed aldol adduct via nucleophilic attack to oxycarbenium ion electrophile formed from the acetal.