Aryl allyl ether, Claisen rearrangement

Rearrangement of aralkyl peroxides 8-35 Rearrangement of allylic aryl ethers (Claisen)... 

Section 24 13 On being heated allyl aryl ethers undergo a Claisen rearrangement to form o allylphenols A cyclohexadienone formed by a concerted six tt electron reorganization is an intermediate... 

The Claisen rearrangemenC is a thermal rearrangement of allyl aryl ethers and allyl vinyl ethers respectively. It may be regarded as the oxa-version of the closely related Cope rearrangement. Claisen has discovered this reaction first on allyl vinyl ethers 1, and then extended to the rearrangement of allyl aryl ethers 2 to yield o-allylphenols 3 ... 

Unlike the acid-catalyzed ether cleavage reaction discussed in the previous section, which is general to all ethers, the Claisen rearrangement is specific to allyl aryl ethers, Ar—O—CH2CH = CH2. Treatment of a phenoxide ion with 3-bromopropene (allyl bromide) results in a Williamson ether synthesis and formation of an allyl aryl ether. Heating the allyl aryl ether to 200 to 250 °C then effects Claisen rearrangement, leading to an o-allylphenol. The net result is alkylation of the phenol in an ortho position. 

Two other important sigmatropic reactions are the Claisen rearrangement of an allyl aryl ether discussed in Section 18.4 and the Cope rearrangement of a 1,5-hexadiene. These two, along with the Diels-Alder reaction, are the most useful pericyclic reactions for organic synthesis many thousands of examples of all three are known. Note that the Claisen rearrangement occurs with both allylic aryl ethers and allylic vinylic ethers. 

Allyl aryl ethers undergo accelerated Claisen and [1,3] rearrangements in the presence of a mixture of trialkylalanes and water or aluminoxanes. The addition of stoichiometric quantities of water accelerates both the trimethylaluminum-mediated aromatic Claisen reaction and the chiral zirconocene-catalyzed asymmetric carboalumination of terminal alkenes. These two reactions occur in tandem and, after oxidative quenching of the intermediate trialkylalane, result in the selective formation of two new C-C bonds and one C-0 bond (Eq. 12.70).153 Antibodies have also been developed to catalyze Claisen154 and oxy-Cope155 rearrangements. 

The competition of Claisen rearrangement and [l,5]-acetyl shift upon thermal treatment of allyl aryl ether 356 resulted in a mixture of the expected Claisen product 357 and its isomer 358 (equation 129)184. It was assumed that the usual Claisen rearrangement (Section IV.E.l) resulted in an equilibrium with the intermediates of successive [3,3]-sigmatropic shifts. The cyclohexa-2,4-dienones 359 and 360 formed leave this equilibrium cycle due to enolization to form the Claisen product 357 or because of [l,5]-shift followed by enolization give the unexpected product 358 (equation 130). 

The allyl aryl ether 183 is converted into the 2-methylbenzofuran in a one-pot procedure via sequential Pd-catalyzed Claisen rearrangement and oxidative cyclization mediated by stoichiometric quantities of 1,4-benzoqui-none (BQ) (Equation 119) <2005OL3355>. 

Allylic aryl ethers, when heated, rearrange to o-allylphenols in a reaction called the Claisen rearrangementIf both ortho positions are filled, the allylic group migrates to the para... 

Substituted allyl aryl ethers undergo a Claisen rearrangement similar to the reaction described in text Section 24.13 for allyl phenyl ether. 2-Butenyl phenyl ether rearranges on heating to give o-( 1-methyl-2-propenyl)phenol. 

The usefulness of the Claisen rearrangement in synthetic work depends on the following facts. The allyl aryl ethers, such as phenyl allyl ether (LX), can be prepared easily in high yields and can be transformed readily in good yields to the 2-allylphenols (LXI). The reaction thus... 

Fig. 14.46. Preparation of an allyl aryl ether and subsequent Claisen rearrangement. (The rearrangement is named after the German chemist Ludwig Claisen. Basically, the name is pronounced the German way but it is known that the family preferred the pronunciation /klaezn/.)...

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