Ethers allyl aryl

Allylic acetates are widely used. The oxidative addition of allylic acetates to Pd(0) is reversible, and their reaction must be carried out in the presence of bases. An important improvement in 7r-allylpalladium chemistry has been achieved by the introduction of allylic carbonates. Carbonates are highly reactive. More importantly, their reactions can be carried out under neutral con-ditions[13,14]. Also reactions of allylic carbamates[14], allyl aryl ethers[6,15], and vinyl epoxides[16,17] proceed under neutral conditions without addition of bases. 

Allyl aryl ethers are used for allylation under basic conditionsfh], but they can be cleaved under neutral conditions. Formation of the five-membered ring compound 284 based on the cyclization of 283 has been applied to the syntheses of methyl jasmonate (285)[15], and sarkomycin[169]. The trisannulation reagent 286 for steroid synthesis undergoes Pd-catalyzed cyclization and aldol condensation to afford CD rings 287 of steroids with a functionalized 18-methyl group 170]. The 3-vinylcyclopentanonecarboxylate 289, formed from 288, is useful for the synthesis of 18-hydroxyestrone (290)[I7I]. 

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... 

Bromo-9-borabicyclo[3.3.0]nonane (9-Br-BBN), CH2CI2, reflux, 87-100% yield.9-Br-BBN also cleaves dialkyl ethers, allyl aryl ethers, and methylenedioxy groups. 

Rearrangement of allyl vinyl ethers or allyl aryl ethers... 

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. 

Allinger, Norman Louis, 130 Allose. configuration of, 982 Allyl aryl ether, Claisen... 

In these cases, of course, the final tautomerization does not take place even when R = H, since there is no aromaticity to restore, and ketones are more stable than enols.The use of water as solvent accelerates the reaction.The mechanism is similar to that with allylic aryl 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 isomerization of allyl aryl ethers catalyzed by 0.1-1.3 mol% RhCl(H)(CO)(PPh3)3 in benzene at 50-60 °C gave Z-isomers as the major products (Scheme 35).62... 

The high-valent metal species required for activation of an alkyne has also been generated by the oxidative addition to an allylic or propargylic system. For example, with an allyl aryl ether as the substrate, this type of reaction achieves a cycloisomerization that occurs through an 0- to C-allyl migration (Equation (92)) 323,324 similarly, (9-propargyl derivatives lead to a mixture of allenyl and propargyl products (Equation (93)).325,326... 

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 Pd-catalyzed electro-cleavage of the C—O bond of allyl aryl ether proceeds smoothly in a DMF-Bu4NBp4-(Mg)-(Stainless Steel) system, giving depro-tected products in 73 99% yield [437]. The sp-sp intermolecular coupling reaction with the Pd water-soluble catalyst prepared in situ from Pd(II) acetate and sul-fonated triphenylphosphine in an MeCN-H2O system yields diynes in 45 65% yields [438]. Similarly, the sp -sp coupling of 2-iodophenols or 2-iodoanilines and terminal alkynes followed by intramolecular cyclization gives indol and furan... 

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... 

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

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