The title compd. 1 undergoes reaction with electrophilic reagents such as dichlorocarbene regioselectively on the p-face endo to the chlorine. The crystal structure of 1 indicates significant geometrical distortions of the two rings, which are attributed to a stabilizing interaction between the C-Cl s* orbital and the exo p-orbital. PM3 calcns. of these orbitals, the electrostatic potential and transition state models for dichlorocarbene addn. all agree with the obsd. regioselectivity.