6.6- Diphenyl-cyclohexa-2,5-dienone

In order to defer stereochemical questions we will consider first the photoreaction of 6,6-diphenyl-cyclohexa-2,5-dienone (6). Either direct or sensitized photolysis<3,7,8) of compound (6) in aqueous dioxane follows the following course ... 

Photochemical rearrangements, in particular the mechanisms, of 4,4-diphenyl-cyclohexa-2,5-dienone have been intensively studied by Zimmerman et al. u7). The main products are 2,3- and 2,4-diphenylphenol. Perst et al.1181 isolated 2,3,4,6-tetraphenylphenol and other substances when 2,4,4,6-tetraphenylcyclohexa-2,5-dienone was photolysed. Other photochemical rearrangements leading to 3-acetoxy-2,4,6-triphenylphenol and 2-acetoxy-3,4,6-triphenylphenol are found in Ref. n9>. 

Trimethylphenol gives the 2-arylated cyclohexa-3,5-dienone derivative. The ortho and para phenylation of phenol with lead tetraphenyl is reported in a US patent53). Depending on the reaction conditions, 2-phenyl-, 2,6-diphenyl- and even... 

Zimmerman 103) applied the well known rearrangement of 4,4-disubstituted cyclohexa-2,5-dienones (e.g. the 4,4-diphenyl derivative tives the 3,4-disubstituted phenols l)). Using acetic anhydride and a small amount of concentrated sulfuric acid, 97.5 % of 3,4-diphenylphenolacetate is formed, which in turn is hydrolyzed to give 3,4-diphenylphenol. This is one of the easiest synthesis of this phenol. 2-Bromo-4,4-diphenylcyclohexa-2,5-dienone rearranges by a similar route to give a 49 % yield of 2-bromo-3,4-diphenylphenolacetate and 47 %2-bromo-4,5-diphenylphenolacetate U4). A [1.2]-phenyl shift of 4-methoxy-2,3,4,6-tetraphenyl-2,5-dienone in acetic anhydride and zinc chloride gives rise to 4-methoxy-2,3,5,6-tetraphenylacetate (m.p. 284 °C, 85% yield)115 . 

Diphenyl cyclopropenyl-idene)cyclohexa-2,5-dienone 0=. 1,3-Disilacyclobutane, 21.2 -15 4a Dichloromelhane, N67 317... 

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