New Products from the Heptalene‐Forming Reaction of Azulenes and Acetylenedicarboxylates in Polar Media

A number of azulenes 1, in particular those with π‐substituents at C(6) such as phenyl, 3,5‐dimethylphenyl, and 4‐biphenyl, have been reacted with 3 mol‐equiv. of dimethyl acetylenedicarboxylate (ADM) in MeCN at 110° (cf. Scheme 1). Main products had been, in all cases, the corresponding heptalene‐4,5‐dicarboxylates 2. However, a whole number of side products, mainly rearranged (1+2)‐adducts with two molecules of ADM, in amounts of 0.2–9% were …