Hindered Nucleophilic Displacement (SN 2) Reactions of 2exo‐ and 2endo‐ Norbornyl Derivatives. Norbornane) Series 4

The reactions of 2exo‐ and 2endo‐norbornyl bromide (1e and 2e, respectively) in 90% ethanol with a large excess of potassium hydroxide, and of 2exo‐norbornyl p‐toluenesulfonate (1g) with excess sodium thiophenolate in methyl cellosolve, have been studied. They obey the first order rate law and are zero order with respect to the base‐nucleophile. However, the ratio of 1,2‐ and 1,3‐elimination to exo‐substitution products depends strongly on the base‐nucleophile concentration. Ion pair intermediates are indicated. The extreme inertness of 2‐norbornyl derivatives in displacement reactions is due to severe steric hindrance of rearside nucleophilic attack, a feature they have in common with other bi‐ and tricyclic molecules bearing nucleofugal groups adjacent to one or two bridgehead atoms.