Fries rearrangement double

A second process that occurs concurrently with the dissociation— redistribution process is an intermolecular rearrangement by which cyclohexadienone groups move along a polymer chain. The reaction maybe represented as two electrocycHc reactions analogous to a double Fries rearrangement. When the cyclohexadienone reaches a terminal position, the intermediate is the same as in equation 8, and enolization converts it to the phenol (eq. 9). 

An increase of char yield is generally reflected as an improvement in oxygen index. In the styrylpyridine based polyesters and polycarbonate an intermolecular thermally induced Diels-Alder reaction has occurred through the double bond, this increased the char yield and decreased the flammability. The Fries rearrangement, as well as dimerization and isomerization, occurred simultaneously during the UV irradiation of p-VPPB, but no dimerization or isomerization occurred for p,p -BVPDPC, probably due to steric effects. 

Photo-Fries rearrangement-. Photo-Fries rearrangement involve migra-fSi of a group across a double bond (1,3 migration) in structures of the Plowing type ... 

The first synthesis of a dimeric pyranonaphthoquinone 225 which is related to naturally occurring biologically active compounds such as actinorhodin and crisamicin includes the double Fries rearrangement of the bis-ether 224 as one of the stages (equation 102). 

The bicoumarin 229 was obtained using a double Fries rearrangement of the diacetate 226 promoted by TiCU as a Lewis acid, and a subsequent cyclization of the dicarbonate 228 derived from the diketone 227 (equation 103) . The Fries rearrangement of hydroxycoumarin chloroacetates 230 provides a new short pathway to furocoumarins 231 (equation 104) °°. 

Out-of-cage reaction leading to the saturation of double bonds (b). Competitively to photo-Fries rearrangement, some -CH2-R radicals formed by direct 0-CH2 scission may add to the double bonds provoking the loss of conjugation. It is indeed well know that radicals can directly add on unsaturations [32]. 

From the infrared absorbance, the approximate concentration of alcoholic function formed on the one hand and of double bonds disappeared on the other hand is calculated using the molar extinction coefficient of both functions ( 90 and 125 L/( mol cm) for -OH and =CH-, respectively). From these values, it was determined that the occurrence of the two photolytical processes is 60/40 for photo-Fries rearrangement over saturation reaction. 

Phenyl benzoate (PB) was chosen as a model for the double Fries rearrangement of diphenyl benzoate into diphenol para monomers (Eq. 4) [4] and its transformation over several solid catalysts was investigated [4,8]. 

The double 1,4-carbamoyl rearrangement to a hydroquinone diamide is performed in 25% yield. The Fries rearrangement is also observed in good yields in the naphthyl- phenanthryl-, pyridyl-, and quinolinyl... 

Geometrical trans to cis isomerization of 3,3 -, 4,4 -, and 5,5 -disubstituted 2,2 -diphenoquinones has been studied by computational methods.The double bond isomerization of butene-catalysed l-ethyl-3-methyl-imidazolium chloride ionic liquid has been similarly examined and stepwise isomerization is suggested.The reaction of l,2-di(l-adamantyl)-2-thioxoethanone with diazomethane and 2-diazopropane gave 2-acylthiiranes via 2 - - 3-cycloaddition, elimination of nitrogen, and 1,3-dipolar electrocyclization of the intermediate acyl-substituted thiocarbonyl ylides. Rearrangement of pyrimidine-5-carboxylic acids esters to 5-acylpyrimidones does not occur in the examples studied and a [l,4]-phospho-Fries rearrangement has been reported. ... 

Retropinacol rearrangements have been applied to triterpenoid 4,4-dimethyl-3/5-ols and their side chain degradation products for example, 14a-methylpregnanes18,19 and 14a-methylandrostanes.18a 20 Side chain and nuclear double bonds, 17/5- and 20-acetoxy, 17/5-carbomethoxy-, and 11- and 20-keto groups do not interfere with ring contraction. However, Fried 18b found that with an 11-ketone, considerable amounts of chlorinated by-... 

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