Aromatic rearrangements

Boron trifluoride etherate was used in conjunction with the reducing agent borane to rearrange aromatic O-triisopropylsilyl ketoximes to cyclic and acyclic aniline derivatives. The steric hindrance of the substituents on the silicon atom, the size of the aliphatic ring and the presence of alkoxy substituents on the aryl group played important roles in the aniline formation. 

A related transformation is the rearrangement-aromatization of ketoisophorone to trimethylhydroquinone diacetate, an intermediate in the industrial synthesis of (all-rac)-a-tocopherol. Of heterogeneous catalysts, Nafion-silica exhibited the best catalyst performance858 [Eq. (5.313)], but activities decreased with repeated use because of the leaching of Nafion resin. 

Keywords Thermal rearrangement Newman-Kwart rearrangement Aromatic thiols... 

When the electron-deficient atom is the nitrogen atom of nitrous acid or nitrosyl chloride, the products will depend on whether the amine is a primary or secondary amine. Primary aliphatic amines give rise to dia-zonium salts (RNj X) which readily decompose, sometimes with rearrangement. Aromatic diazonium salts (ArNj X ) are very important in aromatic transformations, and are discussed later. Secondary amines, on the other hand, give rise to nitrosamines... 

Contraction and Expansion of Steroid Rings The Westphalen and Backbone Rearrangements Epoxide Rearrangements Aromatization... 

HBr in HOAc has been used to effect the rearrangement/aromatization of the androstenone epoxide (40). The use of DBr/DOAc and C NMR analysis led to the conclusion that the reaction takes place via the phenonium ion (41) shown in equation (17). ... 

The final phenol probably arises from reversal of the last two steps. The oxacyclopropane ring can always close again, but eventually the carbocation reacts via an alternative pathway, involving D migration to give the rearranged aromatic product. 

Gagosz has studied a gold(I)-catalyzed process to convert various allyl pentynyl tosylamides to functionalized pyrroles under mild conditions. Alkyne activation by Au(I) triggers a nuclephilic cyclization of tosylamide to generate the presumed alkenyl gold intermediate 385 which undergoes aza-Claisen rearrangement. Aromatization followed by protodemetalation leads to the pyrrole 387. ... 

The most frequently used bases in the above dehydrohalogena-tions are finely divided potassium hydroxide and sodium amide. Alcoholic potassium hydroxide tends to cause the isomerization of 1-acetylenes to internal acetylenes (Favorskii rearrangement). Aromatic acetylenes are not effected. Sodium amide may cause the reverse rearrangement from internal acetylenes to 1-acetylenes. Impure sodium amide may be an ineffective reagent and should not be used since dangerous (explosive) peroxides may be present. 

A rearrangement aromatization of benzo[c]oxepine gives substituted naphthalenes (Scheme 189). ... 

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