title: Substituent effects on rates and torquoselectivities of electrocyclic ring-openings of N-substituted 2-azetines.
abstract: Transition structures for the conrotatory electrocyclic ring-opening reactions of N-substituted 2-azetines were computed with the density functional M06-2X/6-31+G(d,p). A wide range of substituents from π acceptors (e.g., CHO, CN) to π donors (NMe2, OMe) was explored. Acceptor substituents delocalize the nitrogen lone pair and stabilize the reactant state of 2-azetines, while donors destabilize the 2-azetine reactant state. The conrotatory ring-opening is torquoselective, and the transition state for the outward rotation of the N-substituent and inward rotation of the nitrogen lone pair is preferred. This transition structure is stabilized by an interaction between the nitrogen lone pair and the vacant π* orbital. The activation free energies are linearly related to the reaction free energies and the Taft σR(0) parameter.
authors.affiliation: Department of Chemistry & Biochemistry, University of California , Los Angeles, California 90095-1569, United States.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Lopez
authors.forename: K N
authors.initials: KN
authors.lastname: Houk