A highly enantio- and diastereoselective synthesis of highly functionalized isochromans was achieved through an organocatalyzed dominoreaction. Quinidine as the catalyst initiates a peroxyhemiacetalization/oxa-Michael/desymmetrization domino sequence between various 2,5-cyclohexadienone-tethered aryl aldehydes with hydroperoxides to generate the single diastereomers of isochromans appended with a