Site selectivity and regioselectivity in Diels-Alder reactions of 5-methylene-2(5H)-furanone (1) with several acyclic dienes have been investigated. We have found that I consistently reacts specifically at the exocyclic double bond, giving spiro adducts in good yields. Excellent regioselectivity has also been found in either catalyzed or uncatalyzed reactions with unsymmetrically substituted dienes. A kinetic study of the reaction with isoprene has revealed that the observed regioselectivity is a direct consequence of kinetic control over the process. Theoretical calculations have been carried out in order to interpret these experimental results. © 1990, American Chemical Society. All rights reserved.