Terminal substituent effects on the reactivity, thermodynamics, and stereoselectivity of the 8π-6π electrocyclization cascades of 1,3,5,7-tetraenes.

ABSTRACT: M06-2X/6-31+G(d,p) computations are reported for the 8π-6π electrocyclization cascades of 1,3,5,7-tetraenes. The rate-determining step for these cascades is typically the second (6π) ring closure. According to experiment and theory, un- and monosubstituted tetraenes readily undergo 8π electrocyclic ring closure to form 1,3,5-cyclooctatrienes; however, the 6π electrocyclizations of these cyclooctatriene intermediates are slow and reversible, and mixtures of monocyclic and bicyclic products are formed. Computations indicate that di- and trisubstituted tetraenes undergo facile but less exergonic 8π electrocyclization due to a steric clash that destabilizes the 1,3,5-cyclooctatriene intermediates. Relief of this steric clash ensures the subsequent 6π ring closures of these intermediates are bo

SUBMITTER: Patel A 

PROVIDER: S-EPMC4260667 | biostudies-literature | 2014 Dec

REPOSITORIES: biostudies-literature