Wolff-type rearrangement

The chemical reactions of sulphonyl nitrenes include hydrogen abstraction, insertion into aliphatic C—H bonds, aromatic substitution , addition to olefinic double bonds, trapping reactions with suitable nucleophiles, and Wolff-type rearrangement. Hydrogen-abstraction from saturated carbon atoms is usually considered to be a reaction typical of triplet... 

Indole-3-carboxylic acid amides 23a [21, 22] and esters 23b [23] can be obtained by irradiation in dichloromethane (DCM) of the 3-diazo-4-oxo-3,4-dihydroquino-line 21 in the presence of alkylamines, dialkylamines, arylamines or alcohols (ZH in Scheme 12.7), through a Wolff-type rearrangement involving a carbenoid species leading to the ketene-like intermediate 22 (Scheme 12.7). 

Other classes of heterocycles undergo thermolytic fragmentation to give imido-nitrenes, as typified by the thermolysis of 1,5-diphenyltetrazole 41, the intermediates 42 can either cyclize on to an aromatic ring to form benzimidazoles 43 or undergo a Wolff-type rearrangement to carbodiimides 44 (Scheme 7). Thermal decomposition of 2-acyltetrazoles... 

The gas-phase pyrolysis of benzotriazole leads to a Wolff-type rearrangement to 1-cyanocyclopentadiene in nearly quantitative yield 1% of aniline is formed as a by-product (Eq. 22).76,77 The same products are formed by thermal extrusion of 2 CO from isatin.76 Using methyl-substituted isatins, it was shown that the imidoylcarbene and/or diradical intermediates interconvert to the extent of 10-12% via l//-benzazirine prior to formation of... 

Imidoylnitrenes are aza analogs of both vinylnitrenes and acylnitrenes. Not unexpectedly, therefore, the two major reactions are cyclization onto aromatic rings, forming benzimidazoles, and a Wolff-type rearrangement to carbodiimides. 1,5-Diphenyltetrazole (118) forms a mixture of 2-phenylbenzimidazole (119) (23%) and diphenylcarbodiimide (120) (76%) on thermolysis above 200°C.173,174 However, only the benzimidazole was formed by photolysis.175... 

Van Leusen and co-workers464 have presented evidence for the analogous Wolff-type rearrangement of arylsulfonylcarbenes to sulfenes. 

The decomposition of 1,2,3-thiadiazoles gives thioxocarbenes which undergo a Wolff-type rearrangement >. 

In comparison with oxo- and iminocarbenes, cyclization has now become the predominant reaction a Wolff-type rearrangement to allene is not very weU known for simple vinylcarbenes, even though it is thermochemically favorable ... 

The reaction is reversible, for the gas-phase thermolysis of benzocyclopropene under mild conditions pelds the Wolff-type rearrangement product of 22, namely fulvenallene (24) 44). Several other precursors of carbene 22 are known 44-48) (Scheme 3, Table 4). 

Another instance of the sulfoxide as an interested spectator in a photochemical reaction is the generation of a-sulfinyl carbenes [115]. Photolysis (or thermolysis) of the sulfmyl substituted pyrazoline 227 was shown by trapping experiments to generate the carbene 228, which undergoes a Wolff-type rearrangement to generate the sulfine. After loss of sulfur, the ketone 230 is isolated in near quantitative yield. 

Phosphorus-containing carbenes insert into the OH bond of methanol and undergo a Wolff-type rearrangement. The ease of insertion and addition depends on the group attached to the carbene carbon atom. ... 

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