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

Abstract

The kinetics of the electrophilic bromination of three allylic ethers in a nonprotic solvent, 1,2-dichloroethane, has been investigated. Two of them followed a prevalent second-order pathway, while the third one exhibited a classical, clean third order. The second-order pathway in the first two olehns is attributed to electrophilic assistance of the ethereal oxygen to the attacking bromine molecule. in the molecular bromination of 2,4-cisdimethyl-8-oxabicyclo[3.2.1]-6-octen-3-cis-ol, opposite temperature dependences were found for the two different kinetic pathways. An exoergonic process for the second-order reaction was explained by the lesser stability of the bromiranium-bromide ionic intermediate, compared to the bromiranium-tribromide in the third-order profile. (c) 2007 Wiley Periodicals, Inc