A computational study of the thermal opening of benzocyclobutenes to (E)- and (Z)-xylylenes

The structures of eleven 1-substituted benzocyclobutenes and corresponding (E)-o-xylylenes and (Z)-o-xylylenes have been calculated at the Becke3LYP/6-311G(d,p) level. Some o-xylylenes are plane and even some (Z)-isomers. In three cases (substituent: methoxy, amino and formamido groups), the (Z)-isomer is more stable than the (E)-isomer. The regioselectivity of the Diels–Alder reaction between (o)-xylylenes and propene or ethylvinylether is discussed according to the frontier OM coefficients.