Diels-Alder reaction of α-substituted acrylates and α-(methylene)lactones: Conformation of dienophiles and endo/exo selectivity

to 7- and 9 to 11-membered α-(methylene)lactones has been carried out to examine correlation of dienophile structure with endo/exo selectivity. While the conformationally flexible acrylates produced cycloadducts of endo/exo = 59:41 to 74:26, the 5 to 7-membered lactones with rigid s-cis conjugated system provided cycloadducts of endo/exo = 13:87 to 32:68 and the 9 to 11-membered lactones which can take both s-cis and s-trans conformation afforded endo/exo ratios of 37:63 to 57:4