Phenyl allyl ether

The method is essentially that of Merlmg and Jacobi. 140 g of allyl alcohol, CH2. CHCHaOH, are cooled in ice-water. A stream of hydrobromic acid, which may be conveniently generated by dropping bromine on naphthalene and passing the vapors through several bottles containing naphthalene, is then passed m until the liquid is saturated, after which it is boiled under a reflux condenser for one hour, the reaction being  

Under the conditions given very little addition of hydrobromic acid takes place at the double bond, although this would undoubtedly occur on long standing of the saturated solution m the cold. 

The mixture is then poured into water and the crude bromide separated and washed first with normal sodium 

94 g of phenol, 121 g. of allyl bromide, 140 g. of dry potassium carbonate, and 150 g of acetone are boiled for eight hours on the water bath under a reflux condenser In this case potassium carbonate is used to combine with the acid liberated in the alkylation, and the reaction is carried on in a non-aqueous solvent Potassium bromide soon separates and the mixture thickens, to a paste After cooling, water is added and then ether to take up the allyl phenyl ether. The ethereal layer is shaken out twice with 10 per cent sodium hydroxide solution to remove unchanged phenol, washed with a little water, and then dried over potassium carbonate and distilled m vacuo The yield should be 115-30 g., boiling at 85° under a pressure of 19 mm. The purification must be carried out under diminished pressure, as will be seen from the next experiment. 

Allyl phenyl ether is boiled under an air condenser until the temperature no longer rises, a process requiring four to six hours. From an initial temperature of about 190° the thermometer finally rises to about 2200. The gradual increase m boiling point is due to a re- 

A mixture of 188 g. (2.0 moles) of phenol, 242 g. (2.0 moles) of allyl bromide [Org. Syntheses Coll. Vol. 1, 27 (1941)], 280 g. of potassium carbonate, and 300 g. of acetone is heated on the water bath under reflux for 8 hours. Excess water is added, and the mixture is extracted with ether. The ethereal solution is washed with dilute aqueous sodium hydroxide solution, then with water, and the ether is removed by distillation. Distillation of the residual oil gives 230 g. (86%) of allyl phenyl ether. The compound boils at 191-192°/760 mm. and 85°/19 mm. 

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Allyl phenyl ether is pre pared by the reaction of phenol with allyl bromide as described in Section 24 11... 

Q The mechanism of the Claisen rearrangement of other allylic ethers of phenol is analogous to that of allyl phenyl ether What is the product of the Claisen rearrangement of C6H50CH2CH CHCH3 /... 

Claisen rearrangement (Section 24 13) Thermal conversion of an allyl phenyl ether to an o allyl phenol The rearrange ment proceeds via a cyclohexadienone intermediate... 

CLAISEN - IRELAND Rearrangment Rearrangement ol allyl phenyl ethers to o (or p-)allylphenols or of allyl vinyl ethers to y.S-unsaturated aldehydes or ketones (Claisen) Rearrangement ol allyl esters as enolale anions to y.S-unsaturated acids (Ireland)... 

Peroxides. These are formed by aerial oxidation or by autoxidation of a wide range of organic compounds, including diethyl ether, allyl ethyl ether, allyl phenyl ether, dibenzyl ether, benzyl butyl ether, n-butyl ether, iso-butyl ether, r-butyl ether, dioxane, tetrahydrofuran, olefins, and aromatic and saturated aliphatic hydrocarbons. They accumulate during distillation and can detonate violently on evaporation or distillation when their concentration becomes high. If peroxides are likely to be present materials should be tested for peroxides before distillation (for tests see entry under "Ethers", in Chapter 2). Also, distillation should be discontinued when at least one quarter of the residue is left in the distilling flask. 

Allyl groups are subject to oxidative deprotection with Chromiapillared Montmorillonite Clay, -BuOOH, CH2CI2, isooctane, 85% yield. Allylamines are cleaved in 84—90% yield, and allyl phenyl ethers are cleaved in 80% yield. 

Evidence for this mechanism comes from the observation that the rearrangement takes place with an inversion of the allyl group. That is, allyl phenyl ether containing a 14C label on the allyl ether carbon atom yields o-allylphenol in which the label is on the terminal vinylic carbon (green in Figure 18.1). It would be very difficult to explain this result by any mechanism other than a pericyclic one. We ll look at the reaction in more detail in Section 30.8. 

Problem 30.9 When a 2,6-disubslituted allyl phenyl ether is heated in an attempted Claisen rearrangement, migration occurs to give the />-allyl product as the result of two sequential pericyclic reactions. Explain. 

Photoaddhion of electron donor olefins such as vinyl ethers and stilbene to variously methyl and halogeno-substituted 1,4-benzoquinones resulted in the formation of dihydrobenzofurans via a dienone-phenol rearrangement of the primary product spirooxetanes <96H(43)619>. High-temperature water seems to be an alternative to use of acid catalysts or organic solvents by the cyclization of allyl phenyl ethers to dihydrobenzofurans <96JOC7355>. 

Sheldon and co-workers (Elings et al, 1995) have used H-Mordenite to rearrange allyl phenyl ether to 2-allyl phenol and subsequent cyclysation to 2-methyl dihydrobenzofuran. 

The basic pattern of the Claisen rearrangement is the conversion of a vinyl allyl ether to a y,8-enone. The reaction is also observed for allyl phenyl ethers, in which case the products are o-allylphenols. 

Wipf and coworkers used a Claisen rearrangement of allyl phenyl ethers 4-309 followed by an enantioselective carboalumination using the chiral Zr-complex 4-310 and trimethyl aluminum (Scheme 4.67) [104]. After an oxidative work-up of the intermediate trialkylalane, the corresponding alcohols 4-311 were obtained with up to 80% ee and 78% yield. One can also transfer an ethyl group using triethyl aluminum with even better ee-values (up to 92%), but the yields were rather low (42%) due to a more sluggish oxidative cleavage of the Al-C bond. 

Where multiple products are possible, the CMR and MBR have been employed to optimize conditions for formation of specific components of a reaction sequence. Examples discussed below, were obtained by heating organic substrates such as allyl phenyl ether [46] and carvone [47] in water. Rearrangements, addition or elimination of water and isomerizations occurred, with each transformation favored under tightly defined conditions. 

Scheme 2.12 Kinetic and thermodynamic products from allyl phenyl ether in water.

Allyl phenyl ether was heated with water in the MBR for 1 h at different temperatures [46]. It underwent Claisen rearrangement to 2-allylphenol (56% yield) at 200 °C, 2-(2-hydroxyprop-l-yl)phenol (37% yield) at 230 °C and 2-methyl-2,3-dihydro-furan (72% yield) at 250 °C (Scheme 2.12). Support for the reaction sequence was obtained through experiments with authentic intermediates. 

Allyl phenyl ethers are activated by a ruthenium(O) complex, ultimately affording a z7/-benzopyran (Equation (186)).150... 

Claisen rearrangement of allyl phenyl ethers. These were thoroughly studied before the rearrangement of allyl vinyl ethers... 

Some allyl phenyl ethers with an alkyl substituent on the end carbon of the allyl group rearrange to give the normal ortho-Claisen product together with another isomeric O-allyl phenol. The latter, formed by the rearrangement of the normal product, has been established. This is called abnormal Claisen rearrangement, is illustrated by the following example. 

Scheme 171 Samarium-catalyzed cleavage of allyl phenyl ethers.

Claisen rearrangement org chem A thermally induced sigmatrophic shift In which an allyl phenyl ether is rearranged to yield an orffio-allylphenol. kla son, re-o ranj-mont ... 

A unified theoretical explanation using molecular orbital theory has been proposed. Grimme [65] investigated the PFR of phenyl acetate as well as the photo-Claisen rearrangement of allyl phenyl ether and the 3-cleavage of para-substituted phenoxyacetones. A unified description of the three reactions has been invoked according to MNDOC-CI and AMl/AMl-HE calculations. No matter what ex-... 

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