13C NMR spectra of tricyclo[4.2.1.02,5]nonanes and tetracyclo[5.4.1.02,6.08,11]dodecanes

The 13C NMR spectra of tricyclo[4.2.1.02,5]nonanes and tetracyclo[5.4.1.02,6.08,11]dodecanes and their dimethyl derivatives were measured to demonstrate the four‐membered ring annelation effects on the bicyclo[2.2.1]heptane skeleton, and the steric δ‐syn effects of the methyl groups attached to the four‐membered ring on the bridge carbons in these systems.