title: Revisiting Hydrogen [1,5] Shifts in Cyclopentadiene and Cycloheptatriene as Bimolecular Reactions.
abstract: Hydrogen [1,5] shifts are pericyclic reactions and take place typically in 1,3-pentadiene. However, because of structure restriction, the symmetry-allowed thermal reactions of 1,3-cyclopentadiene (CPD) and 1,3,5-cycloheptatriene (CHT) suffer large energy barriers, ΔU(‡) = +26.9 kcal/mol and ΔU(‡) = +37.5 kcal/mol by density-functional theory (B3LYP/6-31G*) calculations, respectively. This theoretical study has shown that exo [4+2] and [6+4] cycloadduct dimers involve novel hydrogen-shift channels. After hydrogen migration, one-center adducts are obtained, which undergo Cope rearrangements leading to the second one-center adducts. From the intermediates, reverse routes lead to CPD and CHT with [1,5] migrated hydrogens. A correlation between cycloadditions and [1,5] and [3,3] sigmatropic rearrangements in pericyclic reactions is also discussed.
authors.affiliation: Department of Chemistry, Nara University of Education, Takabatake-cho, Nara 630-8528, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Yamabe
authors.affiliation: Department of Chemistry, Nara University of Education, Takabatake-cho, Nara 630-8528, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Tsuchida
authors.affiliation: Department of Chemistry, Nara University of Education, Takabatake-cho, Nara 630-8528, Japan.
authors.forename: Shoko
authors.initials: S
authors.lastname: Yamazaki