O-Hydroxyketones

In the reaction of a-sulfonyl carbanion with lactones, the corresponding hydroxy-co-ketosulfones were obtained " . Thus, various o-hydroxyketones were shown by Umani-Ronchi and coworkers to be formed from the corresponding lactones. For example, the reaction of a, a-dilithioalkyl phenyl sulfones with lactones in THF at low temperatures afforded co-hydroxy-jS-ketosulfones which, upon desulfonylation with aluminium amalgam, gave the corresponding hydroxyketones . This process was applied for the syntheses of cis-jasmone and dihydrojasmone by treating y-valerolactone with ds-3-hexen-l-yl phenyl sulfone and n-hexyl phenyl sulfone. ... 

In addition to the examples of coumarin syntheses given in the reviews mentioned above and in the treatise on heterocyclic compounds (B-51MI22400), more recent studies have made use of the Perkin synthesis. These include the use of substituted phenoxyacetic acids to prepare 3-phenoxycoumarins (78CI(L)628> and the synthesis of chlorocoumarins from chlorosalicylaldehydes (81T2613). The use of DBU in place of sodium acetate was necessary to effect the ring closure of a number of o-hydroxyketones (78BCJ1907). 

This route may be extended to the synthesis of flavylium salts through the reaction of an orthoformate with C-acyl derivatives of o-hydroxyacetophenone (72JOU2250). During this synthesis small amounts of 2,6-di-(2-hydroxyaryl)pyrylium salts are produced. If an excess of o-hydroxyketone is used in the reaction, the 2,6-diarylpyrylium salt becomes the major product (73JOU399). 

The combination of Ti(OPr )4 and (BulO)2 or Bu 02I I has been utilized in a number of organic transformations including the Sharpless epoxidation,416 the conversion of alcohols to carbonyl compounds,417 the oxidation of phenols to quinones or ketols,418 and the oxidation of Ti enolates to o-hydroxyketones.419... 

The Fries reaction can also be metal-promoted to afford, under the proper reaction conditions, good yields of specific ortho acyl migration products. For instance, o-bromophenyl pivaloate (248) has been treated at —95 °C with s-butyllithium to afford o-hydroxypivalophenone (249) in 76% yield (equation 178) . Similarly, benzoate 250 gave o-hydroxyketone 251 in 82% yield by treatment with n-butyllithium (equation 179) °. 

Methanesulfonyl chloride I boron fluoride Chromones from o-hydroxyketones... 

Without additional reagents o-Hydroxyketones from l-oxa-3-oxonia-2-boratanaphthalenes s. 32, 898 w.a.r. G... 

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