A FACIALLY DISSYMMETRIC 1,3-CYCLOHEXADIENE AS A DIENOPHILE IN DIELS-ALDER REACTIONS WITH POLYHALOCYCLOPENTADIENES

Diels-Alder cycloaddition of 1,2,3,4,5,5-hexachloro- and of 5,5-dimeth oxy-1,2,3,4-tetrachlorocyclopentadiene (2a and 2b, respectively) to ,9 ).0(4,14).0(9,13)]pentadeca-5,7-diene-3,10-dione (1) occurs in each ca se with highly stereoselective attack of the diene upon that face of t he dienophile which is anti to the carbonyl groups. The corresponding endo,anti adduct (i.e., 6 and 8, respectively) is obtained as the excl usive cycloadduct in each case. The structures of 6 and 8 were establi shed unequivocally via X-ray crystallographic methods. The results of AM1 semi-empirical MO calculations for cycloaddition of 1 to 2a are in accord with experiment.