Phenol Rearrangement

In a general reaction known as the cyclohexadienone phenol rearrangement cyclohexa dienones are converted to phenols under conditions of acid catalysis An example is... 

Cross-conjugated dienones are quite inert to nucleophilic reactions at C-3, and the susceptibility of these systems to dienone-phenol rearrangement precludes the use of strong acid conditions. In spite of previous statements, A " -3-ketones do not form ketals, thioketals or enamines, and therefore no convenient protecting groups are available for this chromophore. Enol ethers are not formed by the orthoformate procedure, but preparation of A -trienol ethers from A -3-ketones has been claimed. Another route to A -trien-3-ol ethers involves conjugate addition of alcohol, enol etherification and then alcohol removal from la-alkoxy compounds. 

The rearrangement of dimethyl 5-hydroxy-l-bcnzothiepin-3,4-dicarboxylate (9, R = OH), the first example of a thermal rearrangement of a thiepin derivative without loss of sulfur,12 is analogous to the oxepin-benzene oxide-phenol rearrangement (cf. Section D,l. Introduction and Section 1.2.5.1). This process is catalyzed by the acidic hydroxy substituent. In fact, if this functional group is modified by an in situ acetylation (R = OAc), the usual loss of sulfur occurs. 

The driving force in the overall reaction (the dienone-phenol rearrangement) is of... 

Photoaddhion of electron donor olefins such as vinyl ethers and stilbene to variously methyl and halogeno-substituted 1,4-benzoquinones resulted in the formation of dihydrobenzofurans via a dienone-phenol rearrangement of the primary product spirooxetanes <96H(43)619>. High-temperature water seems to be an alternative to use of acid catalysts or organic solvents by the cyclization of allyl phenyl ethers to dihydrobenzofurans <96JOC7355>. 

In 1979, workers investigating " the dienone-phenol rearrangement treated (3) with acetic anhydride and got an unknown compound believed to be (4), Treatment with strong acid gave (5), they supposed, but they wanted to synthesise an authentic sample of (5) to check their assignment. This is a tricky problem... 

Rearrangement of di- and poly-alkylbenzenes also takes place readily in the presence of Lewis acid catalysts (p. 163), and in the dienone/phenol rearrangement (p. 115). 

A rearrangement essentially akin to a reversal of the pinacol/ pinacolone change, a retro pinacol reaction, is the dienone/phenol rearrangement,... 

Another abnormal Claisen rearrangement is the product formed on heating phenyl propargyl ether. The normal product O-allenyl phenol rearranges by a [1, 5] hydrogen shift and then there is an electrocylic ring closure to give chromene which is the observed product. 

IV. REARRANGEMENTS OF NON-CONJUGATED DIENES AND POLYENES A. Dienone-Phenol Rearrangements... 

Besides aromatization, the energy resulting from relief of cyclic strain can be a driving force of the dienone-phenol rearrangement. Thus, it was reported that dienone 302 is... 

A related dienediol-phenol rearrangement which can occur by different pathways was reported as a new method for synthesis of the oxepine system180. Protonation of the starting diol 344 produces a cation 345 which can follow normal dienone-phenol rearrangement (path a) when the substituents R2 = Me, Ph and R1 = t-Bu are eliminated in the step 346 — 347. However, when R1 = t-Bu and R2 is a substituted phenyl which decreases the nucleophility, the cationoid intermediate 345 cyclizes to the oxonium ion 348 (path b) which then undergoes deprotonation to give the oxepine 349 (equation 124)180. 

Unusual examples of the dienone-phenol rearrangement include the reactions of 1,4-dihydrosilabenzene 361 which rearranges in two directions upon treatment with BCI3 or during purification on silica gel (equation 131)185. 

Cyclization of p-hydroxybenzylacetone derivatives 72 proceeds when treated with tetra-butylammonium perrhenate and trifluoromethanesulfonic acid in refluxing CICH2CH2CI, affording azaspirodienones 73 in moderate to good yields (equation 31). The azaspiro-dienones are easily transformed into quinolines via dienone-phenol rearrangement ". ... 

Dienes, 11 addition to, 194-198 cisoid conformation, 197, 350 conjugated, 11 Cope rearrangement, 354 cycUsation, 346 cycloaddition to, 348 Diels-Alder reaction, 197, 349 excited state, 13 heat of hydrogenation, 16,194 isolated, 11 m.o.s of, 12 polymerisation, 323 Dienone intermediates, 356 Dienone/phenol rearrangement, 115 Dienophiles, 198, 350 Digonal hybridisation, 5 Dimedone, 202 Dimroth s Et parameter, 391 solvatochromic shifts, 391 solvent polarity, 391 Y and,392 Dinitrofluorobenzene proteins and, 172... 

A number of studies of migratory aptitudes in the dienone-phenol rearrangement (6-5) are in accord with the above. For a discussion, see Fischer Henderson 7. Chem. Soc., Chem. Commun. 1979, 279, and references cited therein. See also Palmer Waring 7. Chem. Soc,. Perkin Trans. 2 1979, 1089 Marx Hahn 7. Org. Chem. 1988, 53, 2866. 

The driving force in the overall reaction (the dienone-phenol rearrangement) is of course creation of an aromatic system.136 It may be noted that 50 and 51 are arenium ions (p. 502), the same as those generated by attack of an electrophile on a phenol.137 Sometimes, in the reaction of a phenol with an electrophile, a kind of reverse rearrangement (called the phenol-dienone rearrangement) takes place, though without an actual migration.I3B An example is... 

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