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| - Remote Substituent Effects on the Oxymercuration of2-Substituted Norbornenes: An Experimental and Theoretical Study
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| - The effect of a remote substituent on regioselectivity in the oxymercuration of 2-substitutednorbornenes has been investigated experimentally and theoretically using density functional theory(DFT). Regioselectivities of 1:1 to 14:1 were observed with various 2-substituted norbornenes. Exo-2-substituted norbornenes always gave greater regioselectivities compared to the correspondingendo-2-substituted norbornenes. The effects of solvents on the regioselectivity have also beenexamined, and ethereal solvents were found to be the best choice giving the optimal yield andregioselectivity. The relative rate of oxymercuration was estimated by competition experiments.The least reactive substrate (X = OAc) gave the highest regioselectivity. According to DFTpredictions, the increased difference between the reaction barriers that results in the greaterregioselectivity is correlated directly with the larger polarity of the CC double bond, which isattacked by the mercury and oxygen. A number of stable exo and endo conformers were predicted.All exo conformers show the same polarity of the double bond, while some endo conformers havea reversal of this polarity. All the conformers except those with the OAc substituent are very closein energy and thus should react. The existence of a mixture of endo conformers with the CCdouble bond of opposite polarity clearly explains a decrease in regioselectivity for the endo species.The origin of the greatest regioselectivity for the OAc-2-norbornenes lies in the fact that theconformer with the largest polarity is notably lower in energy than others due to an internal C−H−Ohydrogen bond.
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