The structures and stereochemistry of the major Diels-Alder adducts of 1, 3-dimethyl-l, 3- cyclohexadiene (2) with methyl vinyl ketone, methyl acrylate, and ethyl propiolate have been established as 4a, 4b, and 6d, re-spectively. Lactonization of acid 4c afforded either novel 6-
