Abstract
A study has been made of some factors affecting the migration or elimination of halogen in the Claisen rearrangement of allyl 2,6-dihalophenyl ethers.In the thermal rearrangement of allyl 2,6-dichlorophenyl ether, carried out in a number of solvents of different dielectric constant, halogen migration proceeds somewhat better in highly polar solvents. However, a competitive reduction to the monohalogenated allylphenol occurs in the presence of oxidizable solvents and/or products. The reaction is also complicated by the catalytic effects of certain solvents and the phenolic products, which give results similar to those obtained with Lewis acids. Stannous chloride acts as a Lewis acid and catalyzes the rearrangement of allyl 2,6-dichlorophenyl ether with simultaneous halogen rearrangement. As well, a competitive reductive removal of the halogen takes place. Results from the rearrangement of allyl 2,6-dibromophenyl ether with zinc chloride and of allyl 2,6-dichlorophenyl ether with zinc bromide, as well as those from the stannous chloride reactions indicate that the halogen migration takes place not only by an allylic shift but also via a competitive halogen substitution probably occurring by an Sn2′ pathway possibly assisted by a zinc halide bridge mechanism and/or an ionic species such as [Formula: see text].
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