title: Solving the Pericyclic-Pseudopericyclic Puzzle in the Ring-Closure Reactions of 1,2,4,6-Heptatetraene Derivatives.
abstract: The ongoing controversy whether cyclization reactions of conjugated allenes or ketenes follow a pericyclic or a pseudopericyclic mechanism has triggered dozens of investigations, which have led to new valuable synthetic routes. In this work, the mechanism of 10 representative cyclization reactions of hepta-1,2,4,6-tetraenes with different terminal groups is investigated utilizing the unified reaction valley approach that registers all electronic structure changes of the target molecule along the entire reaction pathway. A clear differentiation between a purely pericyclic and a purely pseudopericyclic mechanism is established. Additionally, it is found that, by using suitable functional groups, a pericyclic mechanism can be converted into a pseudopericyclic one, which is associated with a steady decrease of the reaction barrier and a continuous change from one mechanism to the other. The energetics of the reaction are confirmed by coupled cluster calculations of the CCSD(T) type. The mechanistic insight gained is used to design new pseudopericyclic reactions with low or no barrier, which will open new synthetic avenues.
authors.affiliation: Departamento de Química Orgánica, Campus Lagoas-Marcosende , 36310 Vigo, Spain.
authors.forename: Carlos Silva
authors.initials: CS
authors.lastname: López
authors.affiliation: Departamento de Química Orgánica, Campus Lagoas-Marcosende , 36310 Vigo, Spain.
authors.forename: Olalla Nieto
authors.initials: ON
authors.lastname: Faza
authors.affiliation: Computational and Theoretical Chemistry Group (CATCO), Department of Chemistry, Southern Methodist University , 3215 Daniel Avenue, Dallas, Texas 75275-0314, United States.
authors.forename: Marek
authors.initials: M
authors.lastname: Freindorf
authors.affiliation: Computational and Theoretical Chemistry Group (CATCO), Department of Chemistry, Southern Methodist University , 3215 Daniel Avenue, Dallas, Texas 75275-0314, United States.
authors.forename: Elfi
authors.initials: E
authors.lastname: Kraka
authors.affiliation: Computational and Theoretical Chemistry Group (CATCO), Department of Chemistry, Southern Methodist University , 3215 Daniel Avenue, Dallas, Texas 75275-0314, United States.
authors.forename: Dieter
authors.initials: D
authors.lastname: Cremer