Preparation of a key tetraene precursor for the synthesis of long acenes

The tetraene 7,7-dimethoxy-2,3,5,6-tetramethylenebicyclo[2.2.1]heptane is a key compound for the preparation of a large variety of acenes protected by a carbonyl bridge. We report here a medium scale preparation in seven steps of this valuable starting material. Diels-Alder addition between 6,6-dimethyl fulvene and maleic anhydride, followed by carboxylation, ozonolysis of the double bond, reduction of the four ester group, then chlorination of the alcohol groups and dehydrochlorination give the target compound in 17% overall yield.