Electrophilic additions to anti-sesquinorbornene. Br-2 in methanol and the addition of acetic acid

The kinetics and products of addition of Br-2 in MeOH to anti-sesquinorbornene (1) have been studied at 25 degrees C in the presence of varying [LiBr]. The products consist of similar to 10% cis dibromide and 90% cis methoxy bromide, the amounts of these being independent of the [Br-]. The kinetics reveal that the reaction proceeds via the addition of Bra, and that Br-3(-) is not a brominating agent for this olefin. Acetic acid is shown to add rapidly to the double bond of 1 in a spontaneous reaction and via an acid-catalyzed process in the presence of HClO4. For the spontaneous reaction a solvent deuterium kinetic isotope effect (DKIE) of 3.3 is observed. Proton inventory plots of k(obs) vs atom fraction of deuterium in the medium indicate that the DKIE arises from a transition state for addition involving two or more protons undergoing changes in bonding. The HClO4-catalyzed addition exhibits a large DKIE of 5.4 and is attributable to a simultaneous attack of HClO4 or ClO4- H2OAc+ and HOAc on the double bond. LiClO4 also catalyzes the addition of solvent; through a process exhibiting a DKIE of similar to 8. Analysis of the various equilibria involved indicates that HClO4 is produced in appreciable amounts when LiClO4 is dissolved in HOAc. Analysis of the kinetic dependence of the rate on [LiClO4] indicates that the active species produced may be the ion aggregate Li+/ClO4-/H2OAc+.