Benzilic acid-type rearrangement

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. 

The well documented oxidation of 1,10-phenanthroline (4) to 2,2 -bipyridyl-3,3 -dicarboxylic acid (53) by alkaline permanganate has been repeated. It is now found that 4,5-diazafluoren-9-one (54) is consistently a coproduct of the reaction in 20% yield.253 This provides a convenient route to this hitherto difficultly accessible compound. The formation of 4,5-diazafluoren-9-one almost certainly occurs by way of the intermediate, but not isolated, l,10-phenanthroline-5,6-dione, which is known to undergo a benzilic acid type rearrangement in the presence of hydroxide ions to give the diazafluorenone. This rearrangement of l,10-phenanthroline-5,6-dione has recently been studied further.115 Under some conditions 5,6-dihydro-5,6-dihydroxy- 1,10-phenanthroline can be isolated with the diazafluorenone. 

Exercise 17-43 Write a mechanism analogous to that for the Cannizzaro reaction for the benzilic acid transformation. What product would you expect to be formed from diphenylethanedione with potassium terf-butoxide in ferf-butyl alcohol Would you expect a benzilic acid-type rearrangement to occur with 2,3-butanedione Give your reasoning. 

Base-catalysed ring fission of 3,4-diphenylcyclobut-3-ene-l,2-diones (103) in 50% (v/v) aqueous DMSO proceeds by rapid reversible addition of hydroxide ion followed by rate-determining benzilic acid-type rearrangement to form an intermediate 1-hydroxycyclopropane-1-carboxylic acid which ring opens to the corresponding (Z)-2-oxo-3,4-diphenylbut-3-enoic acid (Scheme 8).173 This is supported by the value of Hammett p = 1.3 (for variation of substituents on one or both rings), the kinetic solvent effects, and the three-oxygen enrichment of (107) from reaction of (103) in 50% H2 180-DMSO. 

A similar investigation of the base-catalysed ring opening of 3,4-diphenylcyclobut-3-ene-l,2-diones (77) to give (Z)-2-oxo-3,4-diphcnylbut-3-cnoatcs (78) has been carried out in aqueous DMSO.108 The evidence points towards a rapid, reversible addition of hydroxide to one carbonyl, followed by a benzilic acid-type rearrangement to give a cyclopropene intermediate (79), which ring opens. 

The principal synthetic route to diazafluorenes involves the alkaline oxidation of phenanthrolines, presumed to give initially the rarely isolated 5,6-dione which (i) further oxidizes to a bipyridyl dicarboxylic acid (the main product) or (ii) undergoes a benzilic acid type rearrangement followed by oxidative decarboxylation to give diazafluorenones in moderate yields (Scheme 2) <77JPR959>. The process has been reviewed by Summers <78AHC(22)i>. The yields of 4,5-diazafluorenone have been optimized <73AJC2727>. 

P.A. Grieco et al. accomplished the total synthesis of (+)-shinjudilactone and (+)-13-ep/-shinjudilactone via a benzilic acid-type rearrangement. The substrate was exposed to basic conditions and the two desired products were obtained as a 1 1 mixture. Interestingly, when the Cl position was methoxy substituted, the rearrangement failed to take place under a variety of acidic and basic conditions. 

Novelli, A., Barrio, J. R. Carbon-14 tracer studies in the benzilic acid type rearrangement of 1-phenyl-and 1-(4-methoxyphenyl)-2-(3-pyridyl) glyoxal. Tetrahedron Lett. 1969, 3671-3672. 

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. 

The diketone 20 was synthesized from the aldol condensation of aryl methyl ketones 19 and benzil. The benzilic acid type rearrangement of 4-aryl-l,2-diphenyl-2-butene-l,4-diones (20) to 5-aryl-3,3-diphenyl-2,3-dihydro-l. -2-pyrrolones (21) has been accomplished under microwave irradiation using ammonium formate in PEG-200. ... 

The synthesis of ( )-shinjudilactone and ( )-13-e/7/-shinjudilactone (41) involves a benzilic acid type rearrangement. ... 

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

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