Stereochemistry of acid-catalyzed cleavage of 7-chloro-1-methylnortricyclene in deuterated medium; evidence for edge protonation of nortricyclenes

Abstract

Cleavage of 7-chloro-1-methylnortricyclene (1e) in D2SO4–DOAc yields deuterated syn-7-chloro-1-methyl-exo-2-norbornyl acetate (3a-d) (1.04 excess d per molecule) and deuterated anti-7-chloro-1-methy l-exo-2-norbornyl acetate (3b-d) (1.28 excess d per molecule) as the kinetic products. 1H and 2H nuclear magnetic resonance spectroscopic analysis of the corresponding alcohols complexed with Eu(fod)3 shows that deuterium is located endo at C-6 and in the methyl group of the syn-7-chloroacetate, endo at C-6 and C-2, at C-7, and in the methyl group of the anti-7-chloroacetate. That the deuterium at C-6 of both acetates is 80–90% stereochemically pure endo, in our view, establishes that the bond farthest removed from the electron-withdrawing chlorine is preferentially cleaved via edge deuteronation.