Proton Magnetic Resonance Spectra and Stereochemistry of Some 5,6-Disubstituted Bicyclo[2.2.2]oct-2-enes

Abstract

The four adducts obtained from the Diels-Alder condensation between 1,3-cyclohexadiene and cis - and trans - p -chloro-β-cyanostyrene have been characterized from the NMR spectrum of the cyclohexane dicarboxylic acid obtained from chromic acid oxidation of the major trans adduct and from long-range shielding effects of the double bond of the bicyclo[2.2.2]octene system on endo and exo protons. The major adduct of the trans styrene has the cyano group exo to the double bond, whereas the major adduct of the cis styrene has both substituents endo to the double bond. Hydrogenation of the two trans adducts yielded one product, as did the hydrogenation of the two cis adducts, the NMR spectrum being consistent with the expected product in each case. Deuterium exchange on the cyano-bearing carbon was used for identification of the signals. The major cis and trans adducts and their hydrogenation products were converted to the corresponding amines by lithium aluminum hydride reduction. The NMR spectra of these amines are discussed. The usefulness of solvent effects in the separation of overlapping NMR signals is demonstrated by the downfield shift of the signal of the hydrogen attached to the cyano-bearing carbon in pyridine versus deuterochloroform in the six cyano-bicyclic compounds prepared.