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-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene (2a and 2b, respectively) to hexacyclo[10.2.1.0(2,11).0(4,9).0(4,14).0(9,13)]pentadeca-5,7-diene-3,10-dione (1) occurs in each case with highly stereoselective attack of the diene upon that face of the dienophile which is anti to the carbonyl groups. The corresponding endo,anti adduct (i.e., 6 and 8, respectively) is obtained as the exclusive cycloadduct in each case. The structures of 6 and 8 were established 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.