Amines 2,5-cyclohexadienones

Polymerization Mechanism. The mechanism that accounts for the experimental observations of oxidative coupling of 2,6-disubstituted phenols involves an initial formation of aryloxy radicals from oxidation of the phenol with the oxidized form of the copper—amine complex or other catalytic agent. The aryloxy radicals couple to form cyclohexadienones, which undergo enolization and redistribution steps (32). The initial steps of the polymerization scheme for 2,6-dimethylphenol are as in equation 6. 

The basic principle of all diazotizations of aromatic amines with a hydroxy- or a sulfonamido group in the 4-position relative to the amino group involves a deprotonation of the OH or NH group, respectively, after diazotization of the amino group. There is also a case of a deprotonation of a CH group in the 4-position of an aniline derivative, namely in the diazotization of 4-aminophenylmalononitrile (2.41) which, by the sequence of steps shown in Scheme 2-23, yields 3-diazo-6-dicyanomethylene-1,4-cyclohexadienone (2.42), as found by Hartzler (1964). This product can also be represented by a zwitterionic carbanion-diazonium mesomeric structure. 

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-... 

Following the pioneering work of Schultz and others on the solution phase photochemistry of linearly conjugated cyclohexadienones [13], we prepared the achiral benzo derivative 7a (Scheme 3) and studied the solid-state photochemistry of its salts with a series of optically pure amines [14]. Diazomethane workup afforded the expected chiral bicyclic photoproduct 8, whose optical purity was determined by chiral GC. The results are summarized in Table 2. 

In 1968, Qriffiths and Hatt established that although dienylketene (282) (generated as the only photochemical product from cyclohexadienone 281) cyclizes thermally to (281), other thermal cyclizations compete, such as the foimaticxi of the bicyclo[3.1.0]hexenone (283) or solvent (amines or alcohols) addition product (284).The thermal formadm of bicyclo[3.1.0]hexenones (283) from ketenes (282) can be (diotochemically reversed. Thus 2,4-cyclohexadienones (287) can be obtained from 2,S-cyclohexa-dienones (285).The stereospecificity of the thermal ring opening of the bicyclo[3.1.0]hexenones to dienylketenes has been established. 

Chemical interaction between transformation products of both the amine and phenol is involved. Derivatives of cyclohexadienone like 77, deeply coloured compounds with structure of indophenols or BQMI 57 are expected to be formed as intermediates [251], The compound 77 is formally analogous to quinol ethers of 1,4-benzoquinone dioxime 163 (R = tert-butyl, methoxy, phenyl) thermally releasing the corresponding phenoxyl and therefore imparting the antioxidant effect [253]. 

If the /7-position of the amine is blocked by methoxy, methyl, chlorine or bromine groups, the species is stable with respect to dimerisation and higher anodic potentials are required for its further oxidation. However, further decomposition of the tri /7-anisylamine radical cation occurs in the presence of any traces of cyanide ion present in the acetonitrile solution. Primary aromatic amines, like phenols, tend to polymerise upon oxidation unless the o and p positions are blocked. 2,4,6-tri-t-butylaniline in acetonitrile solution yields a fairly stable radical cation which in the presence of water forms 3,5-di-f-butyl-4-amino-2,5-cyclohexadienone. ° ... 

Several other stereoselective transformations have been presented that afford ehiral eyelohexenones, ° ° cyclohexadienones, or cyclopenta-nones. °° For instanee, tandem Michael addition/Wittig reaction of (3-carbo q -2-oxopropylidene) triphenylphosphorane and a,p-unsaturated aldehydes has been developed by employing catalysis by newly designed bullq chiral secondary amine C10. ° The multifunctional 6-carbo3gr-cyclohex-2-en-l-ones were generally obtained in excellent diastereo- and enantioselectivities (Seheme 8.23). 

Cyclohexadieones. Since cyclohexadienones are highly useful synthetic intermediates for natural product synthesis and drug discovery efforts, the catalytic asymmetric desymmetrization of cyclohexadienones has received much attention and several success have been made in recent years. Hayashi et al. [109] developed the first oragnocatalytic asymmetric desymmetrization of cyclohexadieones. Screening different secondary amines revealed that cysteine-derived amine is the most effective organocatalyst, affording the bicyclo[4,3,0]nonene skeleton in... 

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