title: Thermal reactions of 8-methylbicyclo[4.2.0]oct-2-enes: competitive diradical-mediated [1,3] sigmatropic, stereomutation, and fragmentation processes.
abstract: [reaction: see text] At 275 degrees C, 8-exo-methylbicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-methylbicyclo[2.2.2]oct-2-enes, of which the orbital symmetry-allowed si product is only marginally favored over the forbidden sr product; that is, si/sr is 2.4. Accompanying the [1,3] shift are significant amounts of epimerization and fragmentation. The 8-endo epimer 1b, which yields no [1,3] product, experiences primarily direct fragmentation and secondarily epimerization. A diradical intermediate can account for all such observations.
authors.affiliation: Department of Chemistry, Franklin & Marshall College, Lancaster, Pennsylvania 17604-3003, USA.
authors.forename: Xavier S
authors.initials: XS
authors.lastname: Bogle
authors.forename: Phyllis A
authors.initials: PA
authors.lastname: Leber
authors.forename: Lynne A
authors.initials: LA
authors.lastname: McCullough
authors.forename: David C
authors.initials: DC
authors.lastname: Powers