Diazoketones thermal rearrangement

Addition of a-diazoketones derived from (W, A )-tartaric and (S )-glutamic acids, followed by dinitrogen extrusion, afforded enantiomerically pure 1,2-methano[60]fullerenes with an acylated methylene bridge.441 Bestmann and co-workers showed that these adducts can be thermally rearranged to substituted fullerene-fused dihydrofurans. 

The unstable bis-3-methylenethietane 392 is obtained by desulfurization of the thiirane 391 that is derived from 384, The thermal rearrangement of a-diazoketone 362 gives the 2-methylene-3-thietanone 363 in quantitative yield. 

The ylides (241) obtained from 2,5-dichlorothiophene and diazoketones readily undergo a totally different type of thermal rearrangement to give oxathiocines (242) (Scheme 45) <88CCI38,89JOC4822). The rearrangement occurs even with ylides which are not stable enough to be isolated. 

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... 

Finally, a nice combination of a light-induced Wolff reaction of a diazoketone (e. g., 5-108) with a thermal Cope rearrangement, a light-induced Norrish type I cleavage and a recombination was developed by Stoltz and coworkers (Scheme 5.22) [38]. Here, irradiation of 5-108 at 254 nm in a photoreactor afforded the bicy-... 

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. 

The key step of the Amdt-Eistert Homologation is the Wolff-Rearrangement of the diazoketones to ketenes, which can be accomplished thermally (over the range between r.t. and 750°C, photochemically or by silver(I) catalysis. The reaction is conducted in the presence of nucleophiles such as water (to yield carboxylic acids), alcohols (to give alcohols) or amines (to give amides), to capture the ketene intermediate and avoid the competing formation of diketenes. 

Nitrogen extrusion from a-diazoketone and the 1,2-shift can occur either in a concerted manner or stepwise via a carbene intermediate known as the Wolff rearrangement (Scheme 2.58). a-Diazoketones undergo the Wolff rearrangement thermally in the range between room temperature and 750°C in gas-phase pyrolysis. Due to the formation of side products at elevated temperatures, the photochemical or silver-metal-catalyzed variants are often preferred that occur at lower reaction temperature. 

The ketene-alkene cycloaddition gives cyclobutanones in a thermal reaction. Most ketenes are not kinetically stable, so they are usually generated in situ, either by E2 elimination of HC1 from an acyl chloride or by a Wolff rearrangement of an a-diazoketone (see Chapter 2). 

Rearrangement of diazoketones to ketenes thermally, photochemically or catalytically. The rearrangement is the key step in the Amdt-Eistert synthesis, q.v. ... 

Wolff rearrangement of a-diazoketones to carboxylic acid derivatives proceeds via ketenes under photochemical, thermal or metal ion catalysis. " The extrusion of nitrogen and the 1,2-shift can occur either in a stepwise manner via a carbene intermediate 8 or through a concerted process. 

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