Carbon-13 N.M.R. shifts as a measure of transannular interaction in unsaturated alicyclic systems

Abstract

Through-space transannular interaction between formally non-conjugated methylene and carbonyl n-electrons in conformationally rigid 3,7-disubstituted bicyclo[3.3.1]nonanes (1) has been demonstrated by Senda et al. by comparing the ¹³C n.m.r. shift values of the sp² atoms.

This procedure has been extended successfully to include conformationally mobile benzo derivatives (2) of bicyclo[3.3.2]decane and 1,5-disubstituted cyclooctanes (4). It also succeeds for 5,7-disubstituted derivatives (3) of 1,2,4-ethanylylidene-1H-cyclobuta[cd]pentalene where through- bond interaction is known to be involved. The method is concluded to be a general and reliable one for detection of transannular π-electron delocalization and to have potential in prediction of intramolecular cyclizations.