Retro-benzilic acid rearrangement

H. Takeshita and co-workers devised a short synthesis of (+)-hinesol and (+)-agarospirol via a mild base-catalyzed retro-benzilic acid rearrangement of profo-[2+2] photocycloadducts to the desired spiro[4,5]decanedione framework. 

Hatsui, T., Wang, J.-J., Takeshita, H. Synthetic photochemistry. LXVIl. A total synthesis of ( )-hinesol and ( )-agarospirol via retro-benzilic acid rearrangement. Bull. Chem. Soc. Jpn. 1995, 68, 2393-2399. 

A retro-benzilic acid rearrangement was observed affording isomeric roto-[2-1-2]-photocycloadducts 18a and b when a solution of 17 and 18 in... 

In systems which preclude retro-aldol condensations, benzilic acid rearrangement of 11,12-diketones affords normal C-norsteroids in fair yields. For example, 11,12-diketotigogenin (82) is converted to the C-nor-(5oc,9(, 22a)-spirostane (83) in 65 % yield by barium oxide in boiling aqueous methyl-cellosolve. ... 

The first step in the nonreversible degradation reactions is the formation of a reactive a-dicarbonyl species through the p-elimination of a hydroxide ion. The subsequent reaction pathways to all degradation products can be described by just five reaction types, namely, p-elimination, benzilic acid rearrangement, a-dicarbonyl cleavage, aldol condensation, and retro-aldol condensation (see Fig. 7).31 Retro-aldol condensation and a-dicarbonyl cleavage involve C-C bond... 

Reaction of a solution of 3a,17p-diacetoxy-ll-hydroxy-5p-androst-9(ll)-en-12-one (71) in aqueous propanol with potassium hydroxide, followed by an acidic work-up, afforded the lactone (75 76%). Three events are involved in this transformation (Scheme 16), namely retro-aldol equilibration to give the cii-fused c-o-ring system (72) - (73), stereoselective benzilic acid rearrangement (73) - (74) to... 

Retroaldol reaction, ring opening by - 26, 227 Retro-benzilic acid-type rearrangement imidazoles by - 28, 959 Retrodiene scission... 

It has been shown that microwave irradiation speeds up the benzil-benzilic acid rearrangement and increases the yield of product. Spiro ketones of the type (223) have been found to be susceptible to nucleophilic-induced retro-Claisen condensations. These have led to molecular rearrangements that destroy spiro connectivity see Scheme 55. The rearrangements of radical anions derived from aliphatic ketones have been studied using electrochemical techniques. A model system has been unveiled in which nucleophilic catalysis of amide isomerization is characterized for... 

Aldoses generally undergo benzilic acid-type rearrangements to produce saccharinic acids, as well as reverse aldol (retro-aldol) reactions with j3-elimination, to afford a-dicarbonyl compounds. The products of these reactions are in considerable evidence at elevated temperatures. The conversions of ketoses and alduronic acids, however, are also of definite interest and will be emphasized as well. Furthermore, aldoses undergo anomerization and aldose-ketose isomerization (the Lobry de Bruyn-Alberda van Ekenstein transformation ) in aqueous base. However, both of these isomerizations are more appropriately studied at room temperature, and will be considered only in the context of other mechanisms. 

TTie rearrangements of hydroxy-1,4-benzoquinones in alkali are more complex. Under conditions in which polyporic acid (34) is converted, by way of retro-aldol ring cleavage and benzilic rearrangement, into a-benzyl-P-phenylsuccinic acid, cis- and tranr-a-benzylcinnamic acid and oxalic acid, atromentin... 

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