Mild thermolysis of tert-butyl alkynyl ethers furnishes aldoketenes, which undergo facile [2+ 2] cycloaddition reactions with pendant di-and trisubstituted alkenes. A wide variety of cis- fused cyclobutanones are produced in moderate to high diastereoselectivity and good to excellent yields by this method, and free hydroxyl groups are tolerated in the ene-ynol ether starting materials. Enol-ynol ethers also undergo efficient reaction to produce donor– ...
