Electronic Control of Stereoselectivity. 9. The Stereochemical Course of Electrophilic Additions to Aryl-Substituted Benzobicyclooctadienes

Article abstract of DOI:10.1021/ja00414a015

Product and relative reactivity data have been obtained for the photooxygenation, epoxidation, cyclopropanation, oxymercuration, and hydroboration of three differently substituted (aryl) 2-methylbenzobicyclo<2.2.2>octadienes.Syn stereoselectivity was observed in every case, with the level of syn attack being highest with the tetrafluoro derivative 2c (except in the Simmons-Smith reaction where a single isomer was produced in every case).Only small differences in rate were seen with a given reagent.Electronic interactions in these molecules were explored by photoelectron spectroscopy and MINDO/3 calculations.These combined tools served to show that through-space interaction is absent in these molecules.However, through-bond coupling in 2a and 2b leads to olefinic ?-bond disrotation.The relative importance of this effect as well as long-range Coulomb and charge-transfer interactions is discussed.A connection between such subtle electronic influences and stereoselectivity is established, although prevailing steric effects do serve to compress somewhat the syn/anti range available to these systems.