Named rearrangements Wolff

In this section we have explored a number of rearrangement reactions that involve ketenes or ketene-like intermediates. Notice that each of these rearrangements is a name reaction (Wolff, Arndt-Eistert, Hofmann, and Curtius). Don t panic about keeping the specifics of the reactions connected to the names. Most instructors will not ask you to reproduce the reactions by name. However, if your future includes organic chemistry, you wiU see them again and become familiar with them. Of course if your future does not include organic chemistry, at least you can appreciate the predictability and trends these reactions illustrate. 

With 0,-y-unsaturated a -diazo ketones, the resulting [2.1.0]-bicyclic systems (40) were quite unstable and underwent a [2 + 2] cycloreversion to generate ketenes (41), which were then trapped by nucleophiles (Scheme 7). The overall scheme has been named a vinylogous Wolff rearrangement and offers a novel entry to products usually derived from a Claisen rearrangement.102 A recent report describes its application for functionalized angular alkylation in fused ring systems.103 In contrast, the intramolecular re-... 

The rearrangement has a mechanism similar to those of the Hofmann rearrangement of amides, the Lossen rearrangement of acylhydroxamic esters, the Schmidt rearrangement of carbonyl compounds and the Wolff rearrangement of diazoketones. Evidence concerning the mechanism of one can often be applied to the others, and the whole family has been reviewed briefly . Sometimes the distinction is made that the conversion of an acyl azide into an isocyanate or urethane is the Curtius rearrangement whereas the overall sequence is the Curtius reaction, but usually the former name is used for both processes. 

For photochemically generated (2-biphenylcarbonyl)phenylcarbene, several competing intramolecular reactions are observed, namely cyclopropanation of an aromatic nucleus (followed by norcaradiene to cycloheptatriene tautomerization), Wolff rearrangement, C-H insertion, and a carbene-to-carbene rearrangement (see Houben-Weyl, Vol. E19b, pl282). 

Types of reactions such as Fridel-Crafts, Grignard, Meerwin-Ponndorf, Cannizzaro, Clemenson. Wolff-Kishner, Hofmann Degradation, Beckman Rearrangement, Simmons-Smith, Piels-Alder, Wurtz-Fitig, etc. may not be household names to everyone, but they are to many organic chemists. More importantly, literature sources can be searched for these classifications to give an overall perspective to a reaction under study. 

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). 

It was back in 1902 when Ludwig Wolff (1875-1919), a professor of analytical chemistry at the University of Jena, discovered the thermal rearrangement of ethyl 2-diazo-3-oxobutyrate in water to produce ethane-1,1-dicarboxylic acid, a reaction that has since been named after him Although it is now over 100 years old, the Wolff rearrangement is still alive and well, with prominent applications in modern synthetic organic chemistry. The main applications of the... 

Ludwig Wolff (1857-1919) was bom in Neustadt in the Palatinate and was educated at the University of Wtirzburg and Munich Polytechnic. In 1891, he became Professor of Analytical Chemistry at Jena, where he worked with Ludwig Knorr. His name is associated with the Wolff-Kishner reaction (1911) and the Wolff rearrangement (1912). 

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