Rearrangement reactions Wolff rearrangements

Williamson synthesis Wohl-Ziegler reaction Wolff rearrangement Wolff Kishner reduction Wurtz reaction Wurtz-Fittig reaction... 

Wheland intermediates, 41,131,151 Wittig reaction, 233 Wittig rearrangement, 293 Wolff rearrangement, 119 Woodward-Hoftmaim rules, 344 Wurtz reaction, 289... 

The reaction of cyclohexene with the diazopyruvate 25 gives unexpectedly ethyl 3-cyclohexenyl malonate (26), involving Wolff rearrangement. No cyclo-propanation takes place[28]. 1,3-Dipolar cycloaddition takes place by the reaction of acrylonitrile with diazoacetate to afford the oxazole derivative 27[29]. Bis(trimethylstannyl)diazomethane (28) undergoes Pd(0)-catalyzed rearrangement to give the A -stannylcarbodiimide 29 under mild conditions[30]. 

The diazo ketone 3, when treated with silver oxide as catalyst, decomposes into ketocarbene 5 and dinitrogen Na. This decomposition reaction can also be achieved by heating or by irradiation with uv-light. The ketocarbene undergoes a Wolff rearrangement to give a ketene 6 ... 

The Wolff rearrangement is a versatile reaction R can be alkyl as well as aryl most functional groups do not interfere. The generally mild reaction conditions permit an application to sensitive substrates. 

In this section we first discuss photolytic reactions of arenediazonium salts and report on quinone diazides at the end of the section in the context of imaging technology. Diazoalkenes, non-quinonoid diazo ketones, and the Wolff rearrangement are treated in the book on aliphatic diazo compounds (Zollinger, 1995, Chap. 8). 

Wheland intermediate 357 see also Azo coupling reaction, o-complex Wolff rearrangement 80f., 281, 284ff. Woodward-Hoffmann rules 129, 361, 396... 

The Arndt-Eistert reaction (Scheme 2.1) which involves the Wolff rearrangement of diazoketones 13 (prepared from the corresponding commercially available N-protected-a-amino acids 12 by reaction of their mixed anhydrides with diazomethane a cautionary note is warranted here the generation and handling of diazomethane require special precautions) has been used extensively by Seebach and coworkers for the preparation of N-protected /9 -amino acids 14 and /9 -amino acid esters 15 and 16. 

There are several reactions that are conceptually related to carbene reactions but do not involve carbene, or even carbenoid, intermediates. Usually, these are reactions in which the generation of a carbene is circumvented by a concerted rearrangement process. Important examples of this type are the thermal and photochemical reactions of a-diazo ketones. When a-diazo ketones are decomposed thermally or photochemically, they usually rearrange to ketenes, in a reaction known as the Wolff rearrangement.232... 

Scheme 10.14 gives some other examples of Wolff rearrangement reactions. Entries 1 and 2 are reactions carried out under the classical silver ion catalysis conditions. Entry 3 is an example of a thermolysis. Entries 4 to 7 are ring contractions done under photolytic conditions. Entry 8, done using a silver catalyst, was a step in the synthesis of macbecin, an antitumor antibiotic. Entry 9, a step in the synthesis of a drug candidate, illustrates direct formation of an amide by trapping the ketene intermediate with an amine. 

Intramolecular insertion and addition reactions are very rare for alkyl nitrenes. In fact, it is not clear that the nitrenes are formed as discrete species. The migration may be concerted with elimination, as is often the case in the Wolff rearrangement.251... 

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