Investigation of the Early Steps in Electrophilic Bromination through the Study of the Reaction with Sterically Encumbered Olefins

Abstract

His research interests include amide and ester hydrolysis mechanisms, electrophilic additions to multiple bonds, and bioorganic and model enzyme systems.

The generation and trapping of enantiopure bromonium ions

“…2 Milestones in the history of the bromonium ion include Winstein's experiment with 3-bromo-2-butanols to prove the existence of a cyclic symmetrical species, 3 Olah's observation of a bromonium ion by NMR 4 and Wynberg's stable bromonium ion of adamantylideneadamantane, 5 which was subsequently characterised crystallographically and studied by Brown. 6, 7 Herein we report a new milestone: the first generation and trapping of enantiopure bromonium ions to provide enantiomerically pure products. During the course of our investigations, we observed that the attempted chlorination of (±)-bromophenethylalcohol 1 8 with thionyl chloride gave (±)-bromochloride 4 9 (Scheme 1), which was characterised by X-ray crystallography (Figure 1).…”

Competing kinetic pathways in the bromine addition to allylic ethers in 1,2‐dichloroethane: Opposite temperature effects

“…This effect was attributed to the exoergonic formation of one Br 2 -alkene π -complex. These species have not been specifically investigated in the present approach, even if the 1:1 complex is shown by the negative activation energy for the third-order pathway [17]. Moreover, the 2:1 Br 2 -alkene π -complex is not shown in the present case (Fig.…”

“…The key difference between the two intermediates is therefore the anion. In the third-order pathway the anion is a tribromide formed kinetically; in the second-order one the bromide is the kinetic anion, and it is much less stable than tribromide in solvents like DCE (ε = 10) [17]. In this latter case, the tribromide is probably formed only after the very fast equilibration of bromide (Scheme 3).…”

Crystal structure of 2,4’-oxa-2’ -bromo-2,2’ -bisadamantane, C20H27BrO

“…The mechanism of bromination of adamantylidene-adamantane was studied recently [1]. Now we have studied the bromination of 4-eq substituted adamantylidene-adamantanes in aprotic polar solvents like dichloromethane and tetrachloroethane [2].…”