1,2,3,4,9,9-hexachloro-1α,4α,4aα,8aβ-tetrahydro-1,4-methanonaphthalene ( 1) and 1,2,3,4,9,9-hexachloro-1α,4α,6,7-tetrahydro-1,4-methanonaphthalene ( 2) undergo π-facially diastereoselective Diels-Alder reactions with 4-methyl- and 4-phenyl-1,2,4-triazoline-3,5-dione [MTAD and PTAD, respectively] and with N-methylmaleimide (NMM). In contrast with the results of AM1 calculations, those obtained via ab initio calculations performed at the HF/3-21G ∗ level of theory predict that the computed Diels-Alder transition states are synchronous in all cases studied. Furthermore, these computational results account quantitatively for: (i) the observed π-facial selectivities of the various Diels-Alder reactions studied, (ii) the observed relative lack of dienophilic reactivity of NMM vis-à-vis MTAD and PTAD, and (ii) the observed enhanced diene reactivity of 1 vs. 2 in the reactions studied.