Rearrangements aryl groups

An unexpected aryl-group rearrangement was observed during the attempted preparation of 3-arylbenzothiophenes <99TL2909>. For example, the cyclization of thioether 6 in the... 

When a radical is formed in a chain four or five carbon atoms removed from an aryl group, rearrangements that amount to intramolecular aromatic substitutions can occur. The initial radical attack will yield a cyclohexadienyl radical intermediate with an attached five- or six-membered ring, as in Equation 9.109. 

Oxidation of chalcones with Tl(III) salts gives the aryl group rearranged ketals via... 

This rearrangement is general for i,2-diols of the type R2C(OH) C(OH) R2 where the groups R may be alike or different, and may be alkyl or aryl groups. 

With 4,4-diarylcyclohexenones, the di-Tc-methane rearrangement occcurs. In compounds in which the two aryl groups are substituted differently, it is found that substituents which stabilize radical character favor migration. Thus, the p-cyanophenyl substituent migrates in preference to the phenyl substituent in 4 ... 

Oxaziranes which carry an aryl group on nitrogen occupy a special position. Sometimes, they rearrange even at room temperature, so they cannot easily be isolated. For preparative purposes, rearrangement in hot xylene is suitable. For the rearrangements of iV-alkyl-oxa-... 

Substrates can be 1,2-diketones with aryl groups as well as some aliphatic substituents, cyclic and heterocyclic diketones. However the benzilic acid rearrangement is of limited preparative importance. 

Mechanistically closely related is the benzilic acid rearrangement, where an alkyl or aryl group migrates instead of the hydrogen. 

Addition of bromine to 1 in chloroform solution at 10°C led in high yield to the formation of the exo-5-a/ih -7-dibromide 2. No other products were isolated. The formation of this rearranged product can be explained in terms of Wagner-Meerwein rearrangement where migration of the aryl group is involved (eqn. 1). 

The Somme let-Hauser rearrangement competes when Z is an aryl group (see 13-22). Hofmann elimination competes when one of the R groups contains a p hydrogen atom (17-6 and 17-7). 

Bromo-j3-nitrostyrene and triphenylphosphine in dry benzene gave the phosphonium bromide (47). Using methanol as the solvent, the rearranged product (48) was formed, possibly via an azirine intermediate. Substituted -bromo-/3-nitrostyrenes yield the phosphoranes (49) and a phosphonium salt. When the aryl group is electron-donating, the reaction follows a different course to form the styrene (50) by initial attack of the phosphine on halogen. 

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