Hydroxy-acids diketones

Oxidation of benzoin, PhCH(OH)COPh (above) yields benzil, PhCOCOPh (133), and this, in common with non-enolisable 1,2-diketones in general, undergoes base-catalysed rearrangement to yield the anion of an a-hydroxy acid, benzilate anion, Ph2C(0H)C02e (134). This is, almost certainly, the first molecular rearrangement to be recognised as such. The rate equation is found to be,... 

Of trialkyl phosphites the most frequently used is triethyl phosphite (EtO)3P (M.W. 166.16, b.p. 156°, density 0.969) which combines with sulfur in thiiranes [291, 294] and gives alkenes in respectable yields. In addition, it can extrude sulfur from sulfides [295], convert a-diketones to acyloins [296], convert a-keto acids to a-hydroxy acids [297], and reduce nitroso compounds to hydroxylamines [298] Procedure 47, p. 111). 

Raney nickel hydrogenation, produced an epimeric mixture of hydroxy-esters (446 R = C02Et) and diols (446 R = CH2OH). Treatment of the corresponding hydroxy-acids (446 R = CO2H) with methyl-lithium, followed by Jones oxidation, yielded the two epimeric diketones (447) in the ratio 9 1. Aldoliza-tion of (447 / -Me) with potassium t-butoxide gave epipatchoulenone (448 R = H, R = Me) while similar treatment of (447 a-Me) afforded patch-oulenone (448 R = Me, R = H). 

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... 

Periodic Acid Test for vic-Glycols. Vicinal glycols (hydroxyl groups on adjacent carbon atoms) can be detected by reaction with periodic acid. In addition to 1,2-glycols, a positive test is given by a-hydroxy aldehydes, a-hydroxy ketones, a-hydroxy acids, and a-amino alcohols, as well as 1,2-diketones. 

Asymmetric synthesis by means of a cyandiydrin is an imprvtant process in organic synthesis, because the cyanohydrin can be easily converted into a variety of valuable synthetic intermediates, such as a-hy-droxy ketones, a-hydroxy acids, y-diketones, p-amino alcohols, 4-oxocarboxylic esters, 4 xonitriles, a-amino acids and acyl cyanides. More specifically, the (S)-cyanohydrin of m-phenoxybenzaldehyde is a building block for the synthesis of the insecticide deltamethrin, or (IR)-cis-pyrethroids. ... 

Besides the glycols, periodate and lead tetracetate cleave other vicinal poly-oxygenated compounds that are encountered in sugar chemistry such as 2-hydroxyaldehydes, vicinal diketones, a-keto and a-hydroxy acids, and amino alcohols. On paper, scission of a-hydroxyaldehydes by periodates corresponds... 

Reaction with acid chlorides.2 The adduct reacts with aliphatic and aromatic acid chlorides to give phosphate esters of a-hydroxy /3-diketones (1) in yields of 70-90%. The reaction is considered to involve nucleophilic substitution at the carbonyl group of the acid chloride. The esters are hydrolyzed to a-hydroxy-/3-di-ketones readily by refluxing aqueous benzene (12 hrs.). 

Solid catalysts can be used, after being impregnated with chiral modifiers such as amines and a-hydroxy acids. Ketones having a second functionality either a or /3 to the carbonyl and able to coordinate to the metal center give best optical yields. This suggests that direct chelation of the substrate to the metal surface occurs. The reaction is used to produce a- and /3-hydroxy acids or esters and to reduce /3-diketones. Rather drastic conditions of P and T limit its scope to simple compounds. 

Study of the benzilic acid rearrangement of 2,3-diketones has been extended to the 4,4-dimethyl-5,6-unsaturated analogue (680). The product of reaction with alkali is the A-nor-hydroxy-acid (681), derived by a stereo specific migration of the 3,4-bond, following initial attack by hydroxide ion exclusively at C-3. Hydroxide attack at C-2, which would require one of the C-2 oxygen substituents... 

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