title: An unexpected bispericyclic transition structure leading to 4+2 and 2+4 cycloadducts in the endo dimerization of cyclopentadiene.
abstract: The stereospecific endo dimerization of cyclopentadiene takes place through an asynchronous and symmetrical bispericyclic transition structure, which shows a merging of the 4+2 and 2+4 cycloaddition paths. The shape of the transition structure testifies to the presence of attractive Salem/Houk secondary orbital interactions assisting the endo approach.
authors.affiliation: Dipartimento di Chimica Organica, Università degli Studi di Pavia, Viale Taramelli, 10, I-27100 Pavia, Italy.
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Caramella
authors.forename: Paolo
authors.initials: P
authors.lastname: Quadrelli
authors.forename: Lucio
authors.initials: L
authors.lastname: Toma