Diels ‐ Alder Regioselectivity Controlled by Remote Substituents. The Cycloadditions of 1‐(Dimethoxymethyl)‐2,3‐dimethylidene‐ and ‐2,3,5,6‐tetramethylidene‐7‐oxabicyclo[2.2.1]heptanes

The syntheses of 2,3‐dimethylidene‐ and 2,3,5,6‐tetramethylidene‐7‐oxabicyclo[2.2.1]heptanes substituted in position C(1) are reported. The 1‐dimethoxymethyl group in derivatives 2 and 6 controls the regioselectivity of the Lewis ‐acid‐catalyzed Diels ‐ Alder additions with methyl vinyl ketone and butynone. For the EtAlCl 2 ‐catalyzed addition of methyl vinyl ketone to 6 , the regioselectivity can be reversed by a small solvent modification. The tetraene 2 is a versatile reagent for regioselective ‘tandem’ cycloadditions.