2-chloro-1,4-benzodithiin 1,1,4,4-tetraoxide - A conjunctive dienophile for the preparation of tetrasubstituted polycyclic olefins

2-Chloro-1,4-benzodithiin 1,1,4,4-tetraoxide 11 is a reactive dienophile th at forms Diels-Alder adducts with a number of dienes. Adducts 17a-j undergo facile dehydrochlorination to give 2,3-substituted 1,4-benzodithiin tetrao xides 18a-j, which react further with another molecule of diene (the same o r a different one) affording the "double" adducts 19-23. Upon reductive des ulfonylation with sodium amalgam, the latter are transformed to tetrasubsti tuted polycyclic olefins 24-27. These olefins correspond to the cycloadduct s that would theoretically have been formed by the cycloaddition of diatomi c carbon with two molecules of diene, reacting in a Diels-Alder fashion.