2,5-cyclohexadienone ethers

Scheme 7.19. Selective cis or trans double conjugate addition of Et2Zn to cyclohexadienone ether 70.

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... 

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... 

Iron pentacarbonyl and l-methoxy-l,4-cyclohexadiene react as shown by Birch and oo-workera, but in dibutyl ether this solvent has been found superior. The tricarbonyl(methoxy-l,3-cyclohexadiene)iron isomers undergo hydride abstraction with triphenylmethyl tetrafluoro-borate to form the dienyl salt mixture of which the 1-methoxy isomer is hydrolyzed by water to the cyclohexadienone complex. The 2-methoxy isomer can be recovered by precipitation as the hexafluoro-phosphate salt. By this method the 3-methyl-substituted dienone complex has also been prepared from l-methoxy-3-methylbenzene. The use of the conjugated 1-methoxy-1,3-cyclohexadiene in Part B led to no increase in yield or rate and resulted chiefly in another product of higher molecular weight. An alternative procedure for the dienone is to react tricarbonyl(l,4-dimethoxycyclohexadiene)iron with sulfuric acid. ... 

I 7 Copper-catalyzed Enantioselective Conjugate Addition Reactions of Organozinc Reagents Tab. 7.4. Conjugate additions to 2,5-cyclohexadienone monoacetals and ethers. 

The thermal isomerization of a spirocyclic enol ether to the ketone [202] (Eq. 176) is probably a homolytic process. However, it is noted that part of the driving force for the reaction must be the bonding of the ethereal oxygen to a designated donor atom of the cross-conjugated cyclohexadienone moiety. 

Allyl phenyl ether 6-Allyl-2,4-cyclohexadienone o-Allylphenol... 

Disubstituted-2,4-Cyclohexadienones. Irradiation of 6-ace-toxy-6-methyl-2,4-cyclohexadienone (Formula 92) (R = OAc R = Me) in ether containing water gives the unsaturated acid (Formula 93) (R = OAc R = Me) in 79% yield (48). The geometric arrangement of R and... 

The photochemical rearrangements of 2,4,6-trimethyl-6-acetoxy-2,4-cyclohexadienone (Formula 105) are of special interest. Irradiation of Formula 105 in ether containing a good nucleophile such as cyclohexyl amine gives the expected a, -unsaturated amide (Formula 106) (48). In sharp contrast to expectation, irradiation of Formula 105 in ether con-... 

Irradiation of 2,4,6-trimethyl-6-allyl-2,4-cyclohexadienone (Formula 113) in ether containing cyclohexyl amine gives the expected ctfi-... 

Cyclobutenones. Cyclobutenones and cyclobutenediones undergo photochemical rearrangement to unsaturated acids in a manner analogous to that of 6,6-disubstituted-2,4-cyclohexadienones. Irradiation of Formula 133 in ether saturated with water gives Formula 134 (49). In... 

Intramolecular oxidative cyclizations in the appropriately substituted phenols and phenol ethers provide a powerful tool for the construction of various practically important polycyclic systems. Especially interesting and synthetically useful is the oxidation of the p-substituted phenols 12 with [bis(acyloxy)iodo]-arenes in the presence of an appropriate external or internal nucleophile (Nu) leading to the respective spiro dienones 15 according to Scheme 6. It is assumed that this reaction proceeds via concerted addition-elimination in the intermediate product 13, or via phenoxenium ions 14 [18 - 21]. The recently reported lack of chirality induction in the phenolic oxidation in the presence of dibenzoyltar-taric acid supports the hypothesis that of mechanism proceeding via phenoxenium ions 14 [18]. The o-substituted phenols can be oxidized similarly with the formation of the respective 2,4-cyclohexadienone derivatives. 

The classical Claisen rearrangement is the first and slow step of the isomerization of allyl aryl ethers to orlho-a ly lated phenols (Figure 14.46). A cyclohexadienone A is formed in the actual rearrangement step, which is a [3,3]-sigmatropic rearrangement. Three valence electron pairs are shifted simultaneously in this step. Cyclohexadienone A, a nonaromatic compound, cannot be isolated and tautomerizes immediately to the aromatic and consequently more stable phenol B. 

Finally, reactions with O-protected phenol 40 were studied, but only silyl ethers (40s-u, R = TMS, TBDMS) afforded the cyclohexadienone product 41 in good yield. Other protecting groups primarily yielded the biaryl coupling product 42 (Table 9). 

In general, the rate of the reaction of arylation of phenols by aryllead triacetate increases with the electron density of the phenolic substrate. When pyridine is used as a base, no reaction takes place with electron-poor phenols, such as 2,6-dichlorophenol or 2,6-dichloro-4-nitrophenol.45 45a However, the reaction of the sodium salt of perfluorophenol 43 with phenyllead triacetate under more forcing conditions led to a range of products the product of >rtfe -arylation, the 6-aryl-2,4-cyclohexadienone 44 together with minor amounts of the product of / zra-arylation 45 and the unsymmetrical diaryl ether 46 (Equation (43)).69... 

Singular examples to form aromatic ethers are a base-catalyzed, multistep, one-pot reaction of aryl methyl ketones with the appropriate fluorinated arylidenemalonitriles, the mercury acetate assisted synthesis of pentahalophenylvinyl ethers from vinyl acetate and the corresponding phenol, and the radical displacements in aryloxycyclohexadienones (e.g., 27) by halophenols. 2,3-Dichloro-5,6-dicyanohydroquinone (28) and products such as 29 are readily formed when cyclohexadienone 27 is treated with different phenols. 

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