2- 1 - -2,5-cyclo hexadienone

Calculate the equilibrium abundances of 2,4-cyclo-hexadienone and phenol. 

The reaction can be used to prepare hexaethyl-2,4-cyclo-hexadienone, m.p. 44-45°, in 82% yield from hexaethylbenzene and 3,4,6,6-tetramethyl-2,4-cyclohexadienone from durene in over 80% yield. 

The yield of trans-cyclopropane 54 produced by addition of carbena-cyclo-hexadienone 52 to cis-2-butene increases from 5 to 33% if 90% CeFe is added 3 ). 

Kalmus and Hercules pioneered the studies using conventional lamp-flash photolysis. They clearly demonstrated the intermediacy of phenoxy radicals and cyclo-hexadienones in the PFR of phenyl acetate (10) [17,18], Independently, Humphrey and Roller reached similar conclusions from flash-photolysis studies on bis(4-tert-butylphenyl) carbonate [38],... 

Routes to benzoxadiazoles are based on approaches to the tautomeric 6-diazo-2,4-cyclo-hexadienones (Scheme 11) <9UST(247)135>. The appropriate 2-aminophenol hydrochloride is diazo-tized using either sodium nitrite or isoamyl nitrite and the diazonium chloride is then carefully neutralized with sodium carbonate or potassium carbonate. An alternative approach is from the monotosylhydrazone of the appropriate o-benzoquinone. Naphthoxadiazole (6) was prepared, in a manner analogous to the first route of Scheme 11, from 3-amino-2-naphthol <91AG(E)1476>. A slightly modified preparation is described in a later paper the method was applied to the synthesis of [9a- C]naphth[2,3-( ]-l,2,3-oxadiazole from 3-amino-[2- C]-2-naphthol <92Mi 403-03>. 

Cyclohexadienones. The perturbation of the electronic absorption spectra by adsorption on silica gel can have a significant effect on subsequent photochemical reactions. For example, Hart has shown that 2,4-cyclo-hexadienones photochemically degrade cleanly in nonpolar solvents to a ketene (1) but in highly polar solvents or adsorbed on silica gel bicyclic ketone (2) is the predominant product.33 The absorption spectra indicate that in nonpolar solvents the lowest singlet state is the n,n state, from which the formation of the ketene proceeds. This n -n band is obscured by the band in polar media, inversion of the energy levels of the n,n, and the first... 

Evidence for molecular chlorine or bromine as the attacking species in these cases is that acids, bases, and other ions, especially chloride ion, accelerate the rate about equally, though if chlorine dissociated into Cl and Cl, the addition of chloride should decrease the rate and the addition of acids should increase it. The conjugate base of 26 (4-bromo-2,5-cyclo-hexadienone) has been detected spectrally in the aqueous bromination of phenol.1911... 

Mizutani et al. (144) derivatized BHT to 2,6-di- er -butyl-4-methyl-4-methoxy-2,5-cyclo-hexadienone (BMMC) using up the quantitative Coppinger and Campbell reaction of BHT with bromine in methanol. Separation was carried out on a RadialPak /zPorasil column using a hexane-2-propanol mixture as mobile phase. Detection of BMMC was monitored at 236 nm,... 

The Diels-Alder dimerization of 2,6,6-trimethyl-2,4-cyclo-hexadienone to l,4,6,6,9,9-hexamethyl-A3U-tricyclo-[6.2.2.0 2 7]-dodecane-5,10-dione2 facilitates its separation from the major alkylation product, 2,6-dimethylanisole. 

Irradiation of 6,6-dimethyl-2,4-cyclohexadienene (Formula 92) (R = It = Me) in aqueous ether gives the diene acid (Formula 93) (R = R = Me) (48), and in similar fashion 4-methyl-6,6-diacetoxy-2,4-cyclo-hexadienone (Formula 98) gives the acid (Formula 99) (48). Irradiation... 

This difference is probably due to the fact that no O-S bonding can exist in 108, whereas it can for 110. Another point is that 108 is more polar than 109, probably because a zwitterion formula is more favored in 108 than in 109, the energy liberated by the transformation cyclo-hexadienone-phenol being larger than the energy liberated by the transformation anthrone-anthranol. 

Oxidative transformation of phenolic antioxidants by atmospheric nitrogen oxides (NO ) taking place in the polymer matrix should be mentioned. Discoloring cyclo-hexadienones (64 is an example) are formed in the process called gas fading. 

When Finkbeiner first proposed the ketal rearrangement mechanism, this type of reaction was unknown, but similar rearrangements of cyclo-hexadienones have been demonstrated since. Miller (25) has shown that the rearrangement of 4-anilinocyclohexadienones to diaryl ethers is an intramolecular reaction, with a geometry almost identical to that of Reaction 12. 

All the rearrangements in the quinoline series were effected neat without solvents at 200°. Yields were almost quantitative in almost all the instances although more than one product often resulted from a single starting material. The common feature of allylic inversion was clearly established in these migrations. The intermediacy of the cyclo-hexadienone-type structure was also demonstrated. 

In order to verify the possibility of the intervention of a cyclo-hexadienone-type intermediate (5) in the rearrangement to the... 

Alkynyl complexes. These complexes, which are readily available by reaction of an alkynyllithium with chromium carbonyl followed by methylation with CH3OSO2F, undergo facile Diels-Alder reactions with dienes to provide a general route to ,p-un-saturated chromium carbene complexes. The latter undergo benzannelation or cyclo-hexadienone annelation on reaction with an alkyne. A (trimethylsilyl)ethynyl complex is useful because benzannelation results in migration of silicon from carbon to oxygen to provide a protected phenol. 

Reductive cleavage. Selective scission of the oxymethylene bridge of 1 occurs on exposure to SMEAH in THE/ None of the alternate benzoxepin product (3) is formed, since only the jS-oxygen is disposed perpendicularly to the cyclo-hexadienone moiety. The product is an intermediate in a synthesis of vitamin E (4). 

BROMOCYCLIZATION N-Bromosuccini-mide. 2,4,4,6-Tetrabromo-2,5-cyclo-hexadienone. 

For the reactive (M-ketene)+ ions from 36 (R = COOCH3) and the (M-ethylene)+ fragment from 37 (R = COOCH3), this question could be unequivolcally answered in favour of the tighter 4-membered transition state38, If a substituted cyclo-hexadienone radical cation, 40, were produced as a reactive intermediate, the isomerization to 38 as well as 41 would occur with equal probability. This is a direct consequence of the constitutional and stereochemical equivalence of H/D in 40. 

As a rule, the dienone-phenol rearrangements are catalyzed by strong acids (H2SO4, HCl, CFsCOOH), but other catalytic systems were also reported. Thus, the Fe -doped acidic montmorillonite KIO clay accelerates greatly (by factors of 10 to 10 ) the cyclo-hexadienone-phenol rearrangement which occurs in a few minutes at room temperature according to [1,2] and [3,3] pathways (equation 145) . ... 

Photogenerated oxyallyl cations undergo intramolecular cycloadditions when tethered to a furan an example is illustrated in Eq. 16 [44], The cyclo-hexadienone precursors required substituents which provide the right electronic characteristics for the photoconversion to the oxyallyl zwitterions, therefore limiting the versatility of this reaction. 

The C—C coupling proceeds intramolecularly in 4,4 -alkylidene-bisphenols, which contain the bridge with a quaternary carbon atom39 40 under formation of cyclo-hexadienone XXIII. 

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