Halogen Migration and Elimination in the Claisen Rearrangement of Allyl 2,6-Dihalophenyl Ethers

Abstract

-4 study has been made of some factors affecting the migration or elimination of halogen in the Claisen rearrangement of allyl 2,6-dihalophenyl ethers.I n the thermal rearrangement of allyl 2,6-dichlorophenyl ether, carried out in a number of solvents of different dielectric constant, halogen ~liigratio~l 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 conlplicated 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 rearrangenlent of allyl 2,6-dibromophenyl ether with zinc chloride and of ally1 2,G-dichlorophenyl ether with zi~lc bromide, as well as those from the stannous chloride reactions indicate -that the halogen mi,oration takes place not only by an allylic shift but also via a co~npetitive halogen substitution probably occurring by an Ss2' pathway possibly assisted by a zinc halide bridge mechanism and/or an ionic species such as ZnS?\i@.

Umlagerung von Allyl‐aryläthern und Allyl‐cyclohexadienonen mittels Bortrichlorid

“…[26] und die dort angegebenc Literatur). In geringerer Ausbeute (9%) wird auch Allyl-4-allyl-2,3,5,6-tetramethylphenylather (105) mit Bortrichlorid in das entsprechende 0-4,6-Diallyl-und $-4,4-Diallyltetramethylcycloliexadienon (106 und 107) umgelagert ; daneben wird 88% Spaltungsphenol 99 gebildet [14].…”

Rearrangement of Allyl 2,6-Dichlorophenyl Ether on Column Packings During Gas–liquid Chromatographic Analysis

“…Holvever, their retention times were identical \\it11 those of authentic 4-allyl-2,6-dichlorophenol and 7-chloro-2-methylco~~11aran, res~~ectivelj.. These products can be expected, since 4-allyl-2,6-dichloropl1enol is one of the major products from the tlzernzal rearrangement of all1.l 2,6-dichlorophenyl ether, and 7-chloro-2-methylcoumaran is obtained from the acid-catalyzed cyclization of 2-allyl-6-chlorophenol (peal; B) (1,2). Rearrangeme~lt of ally1 2,6-dichlorophenyl ether \vas found to occur also when this ether was passed through the follo\ving columns: column No.…”

“…This coinpound arose from loss of halogen as well as allyl migration. Such loss of halogen has been attributed to reaction nrith sonle oxidizable material sucll as the solvent used for the reaction, a catalyst such as stanilous chloride, or the phenolic products of rearrangeinent (1). What constitutes the oxidizable species during gas-liquid chroinatographic analysis is not linown.…”

“…Reductive reinoval of halogen is most liliely to occur a t the intermediate dienone stage (ecl [I]), \\-here the allylic halide structure is fornled (1). All attempts to isolate for study the intermediate 6-allyl-2,6-dichlorocyclohexa-2,4-die, as had been done for the analogous G-allyl-2,6-dimetl~ylcyclohexa-2,4-dienone (3), have failed, and only 4-allyl-2,G-dichlorophenol \\-as obtained.…”

“…The products of rcarl-nnyement and halogen elimination obtaincd from the Claisen rearrangement of allj,l 2,G-dichlorophen!.I ether have becn found to be stabIc under reaction conditions, and also remain unchanged during ailalysis by gas-liquid chromatogr a p h~, (1). IIo\\ cvcr, the extent, if any, of rearrangement of allj~l 2,G-dichloropheny1 ether itself during gas-liquid chromatographic anaIysis is not Itno\\-n.…”