Cyclization reactions Beckmann rearrangement

The course of the reaction is dependent on the configuration of the oxime. The (Z)-oxime gave 1,2-benzisoxazoles as the primary product while the (E)-oxime generally produced a Beckmann rearrangement product with or without subsequent cyclization to a benzisoxazole (Scheme 167) (67AHC(8)277). Bunnett conducted a kinetic study on the reaction shown in Scheme 167 and determined that cyclization to intermediate (551) was the rate determining step (61JA3805). 

Beckmann rearrangement of ketoketoximes 288 (R,R = alkyl, aryl) with thionyl chloride unexpectedly afforded 2-aryl(or alkyl)amino-4,6-disubstituted pyrylium salts 289 (equation 124). This reaction is the first example of rearrangement/cyclization involving carbonylic oxygen as terminator. ... 

The intermediate may be trapped by other nucleophiles (different from water) and diverse products may be obtained. The interception of the intermediate may occur inter- or intra-moleculary, the latter providing a helpful tool to produce a new ring system (Scheme 9, pathway 2). These reactions are sometimes referred to, respectively, as Beckmann rearrangement-addition and Beckmann rearrangement-cyclization reactions. 

When the oxime precursor for the Beckmann rearrangement contains one or more oxygen atoms placed in the appropriate position, a cyclization reaction may occur. One example of a Beckmann rearrangement-cyclization involving an oxygen atom as... 

These derivatives may be obtained by reduction of the appropriate nitro derivative catalytically or with a metal-acid system, or by Beckmann or Hofmann rearrangements of suitable acyl or carboxamido derivatives. 4-Aminobenzo[6]thiophene has also been prepared by means of a Bucherer reaction with 4-hydroxybenzo[6 Jthiophene. Several 5-aminobenzo[6]thiophenes have been prepared by cyclization reactions of p-acetamino-phenylthio derivatives. 6-Acetaminobenzo[6 Jthiophenes may be obtained from the corresponding 6-acetyl derivative by Schmidt or Beckmann rearrangements. 7-Aminobenzo[6 ]thiophene can also be prepared from 7-hydroxybenzo[6 ]thiophene by a Bucherer reaction (70AHC(ll)l77). 

Bacycr-Villiger oxidation, 122, 124, 168 Bamford-Stevens reaction, 565 Barbier cyclization, 307-308 Beckmann rearrangement, 168, 245-246. 427-428, 429, 446, 539-540 Bentonite, 237, 441... 

The Beckmann rearrangement of ketoximes to the corresponding amides (31), the Fischer indole cyclization, isomerization of epoxides to the corresponding aldehydes, ketones, or alcohols, hydration and ammo-nolysis of epoxides, oxygen-sulfur interchange, formation of diaryl-ureas and -thioureas from condensation of aniline and carbonyl sulfide, and olefin carbonylation occur over zeolite catalysts (62). The oxo reaction over rhodium and cobalt containing zeolites recently has been claimed (22). 

These solid-acid catalysts are, in principle, applicable to a plethora of acid-catalyzed processes in organic synthesis [18]. These include various electrophilic aromatic substitutions, e.g. nitrations, halogenations, and Fiiedel-Crafts alkylations and acylations, and numerous rearrangement reactions such as the Beckmann and Fries rearrangements. Other examples include a variety of cyclization reactions such as Diels-Alder reactions and the synthesis of pyridines and other heterocycles. 

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