Intramolecular Diels-Alder reactions of furans with a merely strain-activated tetrasubstituted alkene: bicyclopropylidene.
Bicyclopropylidene derivs., e.g., I (R = H, OMe), with furan moieties attached on tethers of various length and nature all undergo clean intramol. Diels-Alder reactions with complete endo-diastereoselectivities when heated to 70 - 130 DegC, under 10 kbar pressure. The reaction rates are at least as high or higher than those of analogously tethered methylenecyclopropane-furan derivs., e.g., II, in spite of the fact that the reactive double bond in bicyclopropylidene is tetrasubstituted and not activated by any electron withdrawing group.
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