Reaction mechanisms : Part (ii) Pericyclic reactions

Abstract

This report surveys the 2008 literature on mechanisms of pericyclic reactions. A recurring theme in this year's reports is again catalysis. Several studies addressed the acceleration of pericyclic reactions by electron transfer, protonation, encapsulation-induced preorganization and selective transition state stabilization via hydrogen bonding or Lewis acid complexation. In addition, the mechanisms of a variety of pericyclic reactions leading to interesting polycycles were examined in detail, and several cases of theoretical predictions being verified experimentally were described.

Tunneling Control: Competition between 6π-Electrocyclization and [1,5]H-Sigmatropic Shift Reactions in Tetrahydro-1H-cyclobuta[e]indene Derivatives

“…Previous literature suggests that the MPW1K and B3LYP functionals provide accurate description of the activation barriers for [1,5]­H-shift reactions for cyclopentadiene and Z -1,3-pentadiene derivatives though the MPWIK functional seems to describe tunneling corrections better. , However, the MPW1K functional is found to overestimate the barrier for 6π-electrocyclization. On the other hand, the B3LYP functional has been shown to reproduce the experimental reaction barriers reliably for several pericyclic reactions including 6π-electrocyclization in bicyclo[4.2.0]­octa-2,4-diene derivatives. ,− , Fry has investigated valence tautomerization in a series of substituted 1,3,5-cyclooctatriene into the corresponding bicyclooctadienes and it can be found that B3LYP/6-31G­(d) level of theory reasonably reproduce the experimental barrier and reaction energy for 1,3,5-cyclooctatriene ( 5a ) (see Scheme S1 in Supporting Information). Although they recommended CBS-QB3 level of theory as the superior choice for these set of compounds, high computational cost restricts its application.…”

“…On the other hand, the B3LYP functional has been shown to reproduce the experimental reaction barriers reliably for several pericyclic reactions including 6π-electrocyclization in bicyclo[4.2.0]octa-2,4-diene derivatives. 25,[39][40][41][42][43]53 Fry has investigated valence tautomerization in a series of substituted 1,3,5-cyclooctatriene into the corresponding bicyclooctadienes and it can be found that B3LYP/6-31G(d) level of theory reasonably reproduce the experimental barrier and reaction energy for 1,3,5-cyclooctatriene (5a) (see Scheme S1 in Supporting Information). 43 Although they recommended CBS-QB3 level of theory as the superior choice for these set of compounds, high computational cost restricts its application.…”

“…All the electronic structure calculations for 6π-electrocyclization and [1,5]­H-sigmatropic shift in 2a – 2j were carried out using the hybrid B3LYP functional within density functional theory (DFT). , The B3LYP functional has been shown to provide an accurate estimate for barrier heights and reaction energies in 6π-electrocyclization and [1,5]­H-shift reactions previously. − The 6-31+G­(d,p) basis set was employed . Additional calculations at various others level of theory were also carried to verify the suitability of the B3LYP functional for those transformations.…”