Face Selectivity in the Diels-Alder Additions and Chelotropic Addition of Sulfur Dioxide to 2-(D)Methylidene-3-methylidenebicyclo[2.2.1]heptane

The stereoselectivity of the cycloadditions of 2-(D)methylidene-3-methylidenebicyclo2.2.1]heptane ( 4 ) to various dienophiles has been determined. The exo- vs. endo-face selectivity depends on the type of dienophiles, and for olefinic ones, on the mode of attack (Alder- vs. anti-Alder endo rule). It is > 9:1 with N-phenyltriazolinedione (NPTAD) and ethylenetetracarbonitrile (TCNE), < 1:9 with dimethyl acetylenedicarboxylate (DMAD), 30 ± 5:70 ± 5 with DMAD in the presence of AlCl₃, 15 ± 5:85 ± 5 with dehydrobenzene and 40 ± 5:60 ± 5 with ¹O₂ generated photochemically (Table 1). With para-benzoquinone and maleic anhydride, the exo- vs. endo- face selectivity is < 1:9 and 20 ± 5:80 ± 5, respectively, for their anti-Alder mode of attack; it is 50 ± 5:50 ± 5 and 55 ± 5:45 ± 5, respectively, for their Alder mode of reaction. Under conditions of kinetic control, the chelotropic addition of SO₂ to 4 is endo-face selective.