Auwers reaction

Conversion of coumarones to flavonols by treatment of 2-bromo-2-(a-bromobenzyl)coumarones with alcoholic alkali. 

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Figure 22 represents the main consequences on pyrazole reactivity when a positive charge is present at the 2-position of the nucleus. A similar situation occurs in the indazolium salts, which thermally decompose into an alkylindazole and an alkyl halide, a reaction sequence described by von Auwers. 

In 1908, while working at University of Heidelberg, Auwers and Muller described the transformation of 4-methyl-2-cumaranone (3) to flavanol 6. Thus aldol condensation of 3 with benzaldehyde gave benzylidene derivative 4, which was brominated to give dibromide 5. Subsequent treatment of 5 with alcoholic KOH then furnished 2-methylflavonol 6. In the following years, Auwers published more extensively on the scope and limitations of this reaction. ... 

Method b Compounds B with a side-chain R of the type COCH2X (X = Cl or Br) (formed by a Hoesch condensation199 or Fries rearrangement200 from a corresponding molecule of type A) result in 3(2//)-benzofuranones (von Auwers-Shriner-Anderson reaction). Method c If the side chain R is of the CH2-CO-R type, the benzo-... 

Favorskii reported the conversion of 3-hydroxy-4-heptanone to 4-hy-droxy-3-heptanone, as well as analogous transformations of 2-hydroxy-3-pentanone and 2-hydroxy-4,4-dimethyl-3-pentanone. These reactions were carried out at elevated temperatures, in ethanol solutions containing a small proportion of sulfuric acid. At the same time, Favorskii reported the isomerization of 2-hydroxypropiophenone to l-hydroxy-l-phenyl-2-pro-panone under the conditions of yeast fermentation—a claim which the evidence given hardly justified and which von Auwers and Mauss disputed. However, Temnikova reported that this conversion does take place in both acid and alkaline media, and the list of what appear to be... 

It is interesting to compare early experimental work with the facilities available in a modem laboratory. Von Auwers was the first to separate the chloro ketones from the normal phenolic aldehydes of the Reimer-Tiemann reaction. Identirication and strocture proof by chemical means followed. It is a tribute to von Auwers skill and insight that his identification procedures have withstood the onslaught of modem spectroscopic means. Although the chloro ketones (equations 8-10) have been called the abnormal products of the reaction, in cases where the ortho and para positions are occupied (see equation 10) only ketonic material is obtained.In fact, the presence of the dichloro ketones provides one of the better arguments for the intermediacy of dichlorocarbene in the reaction mechanism. ... 

Both compounds are made by the halogenation of 4-hydroxybenzaldehyde, conversion to the oxime and dehydration to the nitrile according to the following reaction scheme (Auwers and Reis, 1896) ... 

The interconversion of two isomeric furoxans (la lb R1 R2) is one of the most important and characteristic features of the chemistry of these compounds. The existence of this equilibrium was first discovered by Ponzio,23,25 who erroneously considered it to be the interconversion of furoxan (1) and dioxadiazine (2) structures. Auwers was probably the first to ascribe the equilibrium to furoxan interconversion (la lb), suggesting that an intermediate of type 4 was involved.140 The rate of the reaction is very strongly dependent upon the presence or absence of aromatic ring fusion to the furoxan bond c. Reference has already been made to this in Section II,A because the isomerism and the isomerization were both sources of much mystification to early chemists. 

Both linear and angular annulated 2-methylfurobenzopyranones can be prepared by this route <94BCJ1972>. Benzofuran-3-ones (3-hydroxybenzofurans) are available by an intramolecular nucleophilic substitution reaction (Scheme 45), (Auwers-Pohl reaction). 

This reaction is related to the Auwers Synthesis, Baker-Ollis Reaction, Kostanecki-Robinson Reaction dcnd Allan-Robinson Annulation. 

This reaction is closely related to the Baker-Venkataraman Rearrangement and Kostanecki-Robinson Reaction. Regarding the synthesis of flavone derivatives, the Allan-Robinson condensation is also related to the Algar-Flyn-Oyamada (AFO) Reaction and Auwers Synthesis. 

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