The Determination of the Preferred Stereochemistry and the Magnitude of the Hydrogen Isotope Effect for 1,3 Elimination in the Locked Norbornyl System Methyl exo-2-Bromo-1-norbornanecarboxylate-endo, endo-5,6-d2

Methyl exo-2-bromo-1-norobornanecarboxylate-endo,endo-5,6-d2 (1b) has been prepared and solvolyzed at 112° in 80:20 EtOH-H2O buffered with NaOAc. The loss of 85–90% of the deuterium available on the front face of 1b in the formation of the tricyclic ester 6D coupled with a novel analysis established that the endo:exo preference for 1,3 elimination is at least 15:1 to 20:1. A comparison of the solvolytic kinetic isotope effect (1.18 ± 0.04) for 1b and the 1,3-elimination kinetic isotope effect (1.45–1.6) with data for 1,2 eliminations indicates that elimination occurs from the classical, perhaps 1,3 hyperconjugatively stabilized carbocation 20. The endo:exo preference established in this study is used to reinterpret 1,3-elimination data determined by Collins in the solvolysis of deuteriohydroxyphenyl norbornyl tosylates.