The Diels-Alder reactions between vinylindenes (5 or 6) as the dienes with quinoneketals (7 or 8) or with methacrolein as the dienophiles were investigated. The remarkable regioselectivities of these Diels-Alder adducts suggested that the regiopreferences of these dienes and dienophiles in these cases are not a fixed property of each component of the cycloaddition but are mutually contigent. This paper shows how the Diels-Alder reaction between 6 and 8 was applied to the inaugural total syntheses of fluostatin C and E.