Wolff metal catalyzed

Metal-catalyzed decomposition of p,y-unsaturated a -diazoketones 400 in the presence of an alcohol affords rearranged y,8-unsaturated esters 407 this process has been termed the vinylogous Wolff rearrangement193 . Full accounts dealing with the... 

Ketocarbenes (1) are usually generated from the corresponding diazo compounds (3).s Other sources which are occasionally used are a,a-dibromo compounds (4),9 sulfur ylides (5)10 and iodonium ylides (6 Scheme 2).11 The thermal or photochemical decomposition of diazo compounds in the presence of ir-systems is often complicated by indiscriminate side reactions, such as Wolff rearrangements,12 C—H insertions and hydride migrations. To avoid such problems, the use of metal-catalyzed decomposition of diazo compounds is generally preferred.1 2... 

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 transition metal catalyzed decomposition of a-diazo ketones in the presence of alkenes gives access to a variety of cyclopropyl ketones. In contrast to the thermal or photochemical methods, Wolff rearrangement resulting in ketenes is normally not competitive. 

In the thermal, photochemical or metal-catalyzed dediazoniation of a-diazocar-bonyl compounds, ketenes are usually, but not always formed. The reaction is known as the Wolff rearrangement, because it was discovered by Wolff early in this century... 

Finally we will discuss briefly the Arndt-Eistert reaction, mentioned already in the context of the general scheme (8-34) of preparative methods. This reaction (1935) is actually a sequence of three reactions, first a nucleophilic substitution of an acyl chloride by diazomethane, followed by a metal-catalyzed Wolff rearrangement, and finally hydrolysis of the resulting ketene. 

The involvement of transition metal-catalyzed oxidation during the later stages of glycation (post Amadori product formation) provides an obvious link between glycoxidation and late glycation reactions (Hunt and Wolff, 1991a Baynes, 1991 ... 

Products of a so-called vinylogous Wolff rearrangement (see Sect. 9) rather than products of intramolecular cyclopropanation are generally obtained from P,y-unsaturated diazoketones I93), the formation of tricyclo[2,1.0.02 5]pentan-3-ones from 2-diazo-l-(cyclopropene-3-yl)-l-ethanones being a notable exception (see Table 10 and reference 12)). The use of Cu(OTf), does not change this situation for diazoketone 185 in the presence of an alcoholl93). With Cu(OTf)2 in nitromethane, on the other hand, A3-hydrinden-2-one 186 is formed 160). As 186 also results from the BF3 Et20-catalyzed reaction in similar yield, proton catalysis in the Cu(OTf)2-catalyzed reaction cannot be excluded, but electrophilic attack of the metal carbene on the double bond (Scheme 26) is also possible. That Rh2(OAc)4 is less efficient for the production of 186, would support the latter explanation, as the rhodium carbenes rank as less electrophilic than copper carbenes. 

Although they are not dissolving-metal processes, several other important means for effecting reduction of a carbonyl group to methylene can be conveniently discussed at this point. The Wolff-Kishner reaction involves the base-catalyzed decomposition of hydrazones. Alkyl diimides are believed to be formed and then to collapse with loss of nitrogen ... 

Dirhodium(II)-catalyzed reaction of 3-indoIyl a-diazo-ketoester 82 in the presence of hexanamide afforded the Wolff rearrangement product 83 along with the formation of metal carbene N-H insertion product 84. It has been shown that the indole moiety is more prone to 1,2-rearrangement than the phenyl diazoketoester 85, which led to the formation of N-H insertion product 86 exclusively under similar conditions. 

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