Arndt-Eistert rearrangement

Wolff and Arndt Eistert Rearrangements and Related Reactions... 

WOLFF AND ARNDT-EISTERT REARRANGEMENTS AND RELATED REACTIONS... 

The Wolff and Amdt-Eistert rearrangements are probably among the earliest known reactions promoted by silver ions.2,3 Discovered at the turn of the nineteenth/ twentieth century, the Wolff rearrangement allows the transformation of a-diazo-ketones to carboxylic acids,4 while the Arndt-Eistert rearrangement is a similar sequence also leading to carboxylic acids, but including the preparation of a-dia-zoketones from a shorter acid chloride (Scheme 3.1).5... 

Indeed, applied to a-amino acids, the Arndt-Eistert rearrangement leads to (3-amino acids with retention of the configuration of the migrating group. Such... 

Carbene-type Reactions. AgOTf promoted the mild and efficient Arndt-Eistert rearrangement of a diazoketone to the... 

Preparation of the sulfur analogue involves as the first step cyclization of the terephthalic acid derivative 92. The acid is then converted to the acid chloride and this is allowed to react with diazomethane. Rearrangement of the resulting diazoketone (95) under the conditions of the Arndt-Eistert reaction leads to the homologated acid. 

The Arndt-Eistert reaction (Scheme 2.1) which involves the Wolff rearrangement of diazoketones 13 (prepared from the corresponding commercially available N-protected-a-amino acids 12 by reaction of their mixed anhydrides with diazomethane a cautionary note is warranted here the generation and handling of diazomethane require special precautions) has been used extensively by Seebach and coworkers for the preparation of N-protected /9 -amino acids 14 and /9 -amino acid esters 15 and 16. 

Diazoketones (53) may be obtained by the reaction of diazomethane, CH2N2, on acid chlorides, and a subsequent Wolff rearrangement in the presence of water is of importance because it constitutes part of the Arndt-Eistert procedure, by which an acid may be converted into its homologue ... 

Can the organic chemists associated with so-called Named Reactions make the same claim as supermodel Heidi Klum Many scholars of chemistry do not hesitate to point out that the names associated with name reactions are often not the acmal inventors. For instance, the Arndt-Eistert reaction has nothing to do with either Arndt or Eistert, Pummerer did not discover the Pummerer rearrangement, and even the famous Birch reduction owes its initial discovery to someone named Charles Wooster (first reported in a DuPont patent). The list goes on and on... 

An a-diazo ketone 1 can decompose to give a ketocarbene, which further reacts by migration of a group R to yield a ketene 2. Reaction of ketene 2 with water results in formation of a carboxyhc acid 3. The Woljf rearrangement is one step of the Arndt-Eistert reaction. Decomposition of diazo ketone 1 can be accomplished thermally, photochemically or catalytically as catalyst amorphous silver oxide is commonly used ... 

The Arndt-Eistert Synthesis allows the formation of homologated carboxylic acids or their derivatives by reaction of the activated carboxylic acids with diazomethane and subsequent Wolff-Rearrangement of the intermediate diazoketones in the presence of nucleophiles such as water, alcohols, or amines. 

The Wolff rearrangement and the Arndt-Eistert homologation sequence are very useful in organic synthesis. One of the most popular applications involves amino acids. An interesting example has been described as a key reaction in the synthesis of a 14C-labeled amino acid used for deciphering the biosynthesis of penicillin N from glutamic acid (Scheme 3.2).9 This rearrangement proceeds without racemization and can thus be applied in peptide synthesis. 

The Wolff rearrangement is the third step of the Arndt-Eistert homologation of carboxylic acids. Figure 11.25 picks up an example that was discussed in Section 7.2, that is, the homologation of trifluoroacetic acid to trifluoropropionic acid. The first step of the Arndt-Eistert synthesis consists of the activation of the carboxylic acid via the acid chloride. The Q elongation to an a-diazoketone occurs in the second step. 

This ester is one carbon atom short of the full side chain of grandisol, so an Arndt-Eistert reaction was used to lengthen the chain by one atom. First, the ester was converted into the diazoketone with diazomethane and, then, the Wolff rearrangement was initiated by formation of the carbene with a Amdt-Eistert chain extension of ester silver compound at the Ag(II) oxidation state. 

The method described here represents a modified Arndt-Eistert reaction as developed by Newman and Beal.7 This modification gives results that are more reproducible than those of the original Arndt-Eistert reaction and, in general, allows the rearrangement to be carried out successfully on larger-scale runs. The use of triethylamine in the formation of diazo ketones makes possible the use of only one equivalent of diazomethane.8... 

The Arndt—Eistert synthesis was investigated by Marquardt who obtained 3-diazoacetyl-l,2,5-thiadiazole (92) in good yield from 3-chlorocarbonyl-l,2,5-thiadiazole (81) and diazomethane. When the WolflF rearrangement of 92 was carried out in the usual manner, i.e., with silver oxide as a catalyst, ring degradation resulted and none of the expected l,2,5-thiadiazole-3-acetic acid (93) was isolated. By... 

A useful reaction of acyl chlorides is with diazomethane. The initial product, a diazo ketone, undergoes a rearrangement with the expulsion of nitrogen and the insertion of a methylene group. This Arndt-Eistert reaction is a useful chain-extension procedure (Scheme 3.69). 

The photolytic rearrangement of sulfoxonium ylids is envisaged as taking place via a ketene in a process reminiscent of the Arndt-Eistert reaction viz. 

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