Benzil-benzilic acid

Some reactions that belong in this category have been considered in earlier chapters. Among these are the Tollens condensation (16-46), the benzil-benzilic acid rearrangement (18-6), and the Wallach rearrangement (18-43). 

It has been reported that compound 16 with alkali rearranges to phenyl-1,2-cyclobutenedione, 3 (Section 26-2E). This reaction appears to be the first reported reverse benzil-benzilic acid rearrangement (Section 26-4E). Explain how and why this process occurs. 

The Benzil-Benzilic Acid Rearrangement l/0-Hydro,3/oxido-(l/ 2/aryl)-Hiigro-addition... 

When treated with base, a-diketones rearrange to give the salts of a-hydroxy acids, a reaction known as the benzil-benzilic acid rearrangement (benzil is... 

Polackova, V., Toma, S. Effect of ultrasound on the benzil-benzilic acid rearrangement under phase-transfer conditions. Chemical Papers 1996,50, 146-147. 

Yu, H.-M., Chen, S.-T., Tseng, M.-J., Chen, S.-T., Wang, K.-T. Microwave-assisted heterogeneous benzil-benzilic acid rearrangement. J. Chem. Res., Synop. 1999, 62-63. 

Dienone-phenol rearrangements are mechanistically diverse. They may involve 1,2-shifts of the Wag-ner-Meerwein type, or of the benzil-benzilic acid kind 1,3-shifts by a Claisen-Cope mechanism 1,5-sigmatropic shifts Favorskii-like reactions and other types. They may also be induced photochemically. A number of reviews are available, which discuss mechanistic aspects in detail. In this chapter emphasis is put on preparative aspects of these reactions and the examples are organized on a structural basis, stressing the new bond(s) formed. 

The product is the sodium salt of the a-hydroxycarboxylic acid, which in this case is benzilic acid. Accordingly, this reaction is called the benzil-benzilic acid rearrangement. 

In the benzil-benzilic acid rearrangement, an a-diketone is treated with a base to give the sodium salt of an a-hydroxy carboxylic acid. In the Favorskii rearrangement, an a-halogenoketone is treated with an alkoxide anion to give the a-alkyl ester. This reaction may also be used to effect a ring contraction. 

Benzil-benzilic acid rearrangement The rearrangement of a 1,2-diketone aromatic species in the presence of hydroxide anion to give the a-hydroxycarboxylic acid. 

Bromosinomeneine ketone [lxxvi]. can be made to undergo the benzil —> benzilic acid transformation in hot alkali, the product being 1-bromosinomenilic acid [xcm]. This acid is also obtained when the amorphous product of bromination of 1-bromosinomeninone with one equivalent of bromine is treated with alkali, and from sinomenine hydrate and one equivalent of bromine [69]. 

Pipanzolate Bromide, /. i thyl-3.[(bydroxydiphe-n lacefyi />xy]-I -methylpiperidr ni u m bromide I-ethyf-3-hydroxy-1 -methylpipe rid in ium bromide benzilate benzilic acid, 1-ethyl-3-piperidyl ester methyl bromide JV-ethyl-3-... 

The only known taxoid with 11( 15—> 1), 11( 10— >9) bisabeotaxane skeleton is wallifoliol (232) from T. wallichiana (134). A benzil-benzilic acid type rearrangement of 10-dehydro-10-deacetyl-ll(15—>l)-abeobaccatin 111 (A) might be the biosynthetic pathway of this compound. 

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