Remote substituent effects on regioselectivity in the Pauson–Khand reaction of 2-substituted norbornenes

The effect of a remote substituent on the regioselectivity in the Pauson–Khand reaction of 2-substituted norbornenes has been investigated. Moderate level of regioselectivity was observed and the regioselectivity increases as the electron-withdrawing power of the remote substituent increases. exo Substituents at C-2 of norbornenes generally gave a higher regioselectivity than the endo substituents.