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Photo-Wolff reaction

Intramolecular addition of carbenes to pendant alkenes also provides a cyclization path as e.g., the irradiation of the diazoketone 402 in benzene. No photo-Wolff reaction, rearrangements of the type described in the next section, occurs and the two products... [Pg.422]

Light can be used to promote the Wolff rearrangement, too, and in this case the reaction is called the photo-Wolff rearrangement. The photo-Wolff rearrangement is probably a nonconcerted reaction. First, N2 leaves to give a free carbene, and then the 1,2-alkyl shift occurs to give the ketene. [Pg.89]

Explain the following concepts and keywords photochromism photoswitching photoinitiator photoaffinity labelling photo-Wolff rearrangement photoactivatable compound Barton reaction photochemical trigger photolabile linker photoamination redox photosensitization. [Pg.380]

In aqueous solutions, 2-halophenols, such as 2-bromophenol, are known to undergo photo-Wolff rearrangement (see also Scheme 6.171). In this reaction, the cyclopentadie-necarboxylic acid derivatives 487 are formed via the singlet a-ketocarbene (488) and ketene (489) intermediates, followed by nucleophilic addition of water (Scheme 6.238).1344-1346... [Pg.400]

In summary, the method described here provides an efficient and convenient route to a variety of a-diazo ketones including unsaturated derivatives that were not previously available by diazo transfer. a-Diazo ketones serve as key intermediates in a number of important synthetic methods including the Arndt-Eistert homologation, the photo-Wolff ring contraction strategy, and the carbenoid-mediated cyclopropanation reaction. We anticipate that improved access to a-diazo ketones will serve to enhance the utility of these valuable synthetic strategies. [Pg.230]

There is no doubt that matrix isolation experiments have provided many examples of great interest in this and other areas where reactive intermediates are produced, a-Diazoketones were discussed in an earlier section since the singlet state reaction undergoes the well-known photo-Wolff process. Other studies on these compounds in matrices at 77 K have shown that the diazoketones 571 and 572 undergo equilibration via an oxirene intermediate. Again this is an example of intramolecular trapping . Others have also observed the formation of oxirenes and the existence of a keto-carbene/oxirene equilibrium in a variety of systems, such as the diazoquinone 573. ... [Pg.439]

This has been synthesized starting from the 2+2 cycloadduct between cyclopentenone and cyclobutene by introducing the diazo function and applying the Wolff rearrangement for building a tricyclic alkene. A further photochemical cycloaddition with a cyclopentenone derivative, followed by a new introduction of the diazo function, photo-Wolff rearrangement, and reduction of the acidic function for enabling insertion of the chain lead to the acid, after this succession of (five ) photochemical reactions (Scheme 6.19). [Pg.176]

Beckmann rearrangement, 4, 292 pyrolysis, 4, 202 synthesis, 4, 223 Wittig reaction, 4, 294 Wolff-Kishner reduction, 4, 291 Indole, 1-acyl-2,3-disubstituted photoisomerization, 4, 204 photo-Fries rearrangement, 4, 204 photoisomerization, 4, 42 synthesis, 4, 82 Indole, 2-acyl acidity, 4, 297 synthesis, 4, 337, 360 Indole, 3-acyl-acidity, 4, 297 cleavage, 4, 289 reduction, 4, 289 synthesis, 4, 360 Indole, 7-acyl-synthesis, 4, 246... [Pg.666]

There are several transformations 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. An important example of this type of reaction is the thermal and photochemical reactions of x-diazoketones. When z-diazoketones are decomposed thermally or photo-chemically, they usually rearrange to ketenes. This reaction is known as the Wolff rearrangement. [Pg.641]

Microwave irradiation has been used to modify selectivity in rearrangement and coupling reactions. Indeed, the photo-Fries rearrangement described above could also be classified in this section [56]. Sudrik described the Wolff rearrangement of a-diazoketones under conventional heating and microwave irradiation [76]. The... [Pg.257]

Diazoketones give rearranged products when decomposed thermally or photo-chemically. The reaction is known as the Wolff rearrangement and is of synthetic importance, since it constitutes a convenient method for one-carbon homologation... [Pg.322]


See other pages where Photo-Wolff reaction is mentioned: [Pg.342]    [Pg.302]    [Pg.303]    [Pg.423]    [Pg.425]    [Pg.429]    [Pg.430]    [Pg.342]    [Pg.302]    [Pg.303]    [Pg.423]    [Pg.425]    [Pg.429]    [Pg.430]    [Pg.692]    [Pg.449]    [Pg.692]    [Pg.264]    [Pg.120]    [Pg.382]    [Pg.248]    [Pg.397]    [Pg.546]    [Pg.223]    [Pg.593]    [Pg.133]    [Pg.96]    [Pg.385]    [Pg.73]   
See also in sourсe #XX -- [ Pg.423 , Pg.429 ]




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