Electrophilic Additions toanti-Sesquinorbornene. Br2in 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 °C in the presence of varying [LiBr]. The products consist of ∼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 Br 2, 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 HClO 4 . 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 HClO 4 -catalyzed addition exhibits a large DKIE of 5.4 and is attributable to a simultaneous attack of HClO 4 or ClO 4 - H 2 OAc + and HOAc on the double bond. LiClO 4 also catalyzes the addition of solvent through a process exhibiting a DKIE of ∼8. Analysis of the various equilibria involved indicates that HClO 4 is produced in appreciable amounts when LiClO 4 is dissolved in HOAc. Analysis of the kinetic dependence of the rate on [LiClO 4 ] indicates that the active species produced may be the ion aggregate Li + /ClO 4 - /H 2 OAc + .