Benzilic ester rearrangement

A variant is represented by the benzilic ester rearrangement, where an alkoxide is used as nucleophile. The alkoxide should not be sensitive towards oxidation. The reaction product is the corresponding benzilic acid ester 5 ... 

Screttas, C. G., Micha-Screttas, M., Cazianis, C. T. The benzilic ester rearrangement. Evidence for a set pathway in the benzilic ester and/or acid rearrangement. Tetrahedron Lett. 1983, 24, 3287-3288. 

An alternate rearrangement known as benzilic ester rearrangement occurs in presence of alkoxide as nucleophile. The rearrangement product is the corresponding benzilic ester. 

Evidence for the existence of a single electron transfer mechanism for the benzilic ester rearrangement of benzil and 9,10-phenanthrenoquinone in the presence of lithium r-butoxide in tetrahydrofuran-benzene mixture was reported by Screttas et al They showed that the reaction with lithium t-butoxide occurred cleanly, while the usage of other alkoxides such as LiOEt... 

Benzilic acid rearrangement Benzoin reaction (condensation) Blanc chloromethylation reaction Bouveault-Blanc reduction Bucherer hydantoin synthesis Bucherer reaction Cannizzaro reaction Claisen aldoi condensation Claisen condensation Claisen-Schmidt reaction. Clemmensen reduction Darzens glycidic ester condensation Diazoamino-aminoazo rearrangement Dieckmann reaction Diels-Alder reaction Doebner reaction Erlenmeyer azlactone synthesis Fischer indole synthesis Fischer-Speior esterification Friedel-Crafts reaction... 

With alkoxides, the benzilic acid rearrangement can lead directly to esters by the same sort Ph of mechanism. 

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. 

In the benzil analog (107) a benzilic acid rearrangement leading to the acid (108) can be done and the acid isolated either as a salt or as the methyl ester prepared with diazomethane at a low temperature. The surprise lies in the fact that the acid (108) is unexpectedly unstable in the free state what... 

This reaction has general application for preparing benzilic acids and their esters which have important biological activities. The formed benzilic acid can be used as reducing reagent to transform Qf, -unsaturated ketones into saturated ketones.In addition, the benzilic acid rearrangement on cyclic of-diketones will lead to ring contracted products 2ii, 2kk, 2nn... 

The cycloaddition of allal derivative 24 with dichloroketene followed by treatment of NaOMe in methanol afforded 1,2-dideoxy-P-D-altropyranoside 25 and dimethyl ketal 26 in 36 and 29% yields respectively. " In contrast to NaOMe, chlorocyclopropanated sugar 27 was also isolated in the case of NaOEt in ethanol. It has been suggested that the formation of ethyl ester 25a and chlorocyclopropanated sugar 27 proceeds through the same intermediate 28. Favorskii type reaction pathway has been ruled out due to ring strain in chlorocyclopropanone 28b. Alternatively, benzilic acid rearrangement has been proposed as more probable reaction pathway through common intermediate for 25,25a and 27. 

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