Potassium permanganate hydroxylations

In teirakis(tnfluoromethyl)aZ/eMe, potassium permanganate hydroxylates one double bond [44], the resultmg enol tautomenzes to an a-hydroxykewne (equation 37). 

Carbonyl-containing and unsaturated materials are removed by treatment with sodium borohydride (227,228) and boric acid (229). Other methods used to remove carbonyl impurities include treatment with hydroxyl amine hydrochloride, potassium permanganate, or A/-hydroxyben2enesulfonamide (229). 

Fluonnated alkenes with one fluonne atom attached to the double bond are converted to a-hydroxyketones by potassium permanganate [30] (equation 22) a-Diketones are formed by permanganate hydroxylation of double bonds flanked by fluonne atoms [31] (equation 23)... 

Potassium permanganate, usually in alkaline conditions, using aqueous or aqueous-organic solvents, is a widely used oxidant for effecting syn-vicinal hydroxylation of alkenes (Eq. 3.13). However, overoxidation or alternative oxidation pathways may pose a problem, and the conditions must be carefully controlled.62... 

Limiting the reaction to hydroxylation alone is often difficult but usually attempted by using cold, dilute, and basic solutions of potassium permanganate. 

A base-catalyzed, elimination reaction was a key step in a synthesis of D-ribose from L-glutamic acid.188 In that work, L-glutamic acid was converted, by a series of reactions, into 5-0-benzyl-2,3-dideoxy-D-glycero-pentofuranose (157) from compound 157, a mixture of glycosides was obtained which, on treatment with bromine and calcium carbonate, gave the monobromo derivative 158 as a mixture of diastereoisomers. Base-catalyzed dehydrobromination of 158 afforded the unsaturated derivative 159. Hydroxylation of 159 with potassium permanganate or with osmium tetraoxide gave a mixture of methyl 5-0-benzyl-/3-D-ribofuranoside and methyl 5-O-benzyl-a-D-lyxofuranoside. 

Both of the stereoisomeric DL-tetroses were obtained21 from 1,1-diethoxy-2-butyn-4-ol (18a). In two steps, involving acetylation of 18a and partial hydrogenation of the triple bond in derivative 18b, cis-4-acetoxy-l,l-diethoxy-2-butene (19) was prepared. ci.s-Hydroxylation of 19 with potassium permanganate, followed by acetylation, led to 20. Hydrolysis (basic, and then acidic) of the protecting groups yielded DL-erythrose (28%). 

A very efficient, stereospecific synthesis of DL-ribose was based26 on the use of l,l-diethoxy-5-(tetrahydropyran-2-yloxy)-2-pentyn-3-ol as the substrate. Catalytic hydrogenation of this alkyne to the cts-alkene was accompanied by cyclization, to give 2-ethoxy-2,5-dihydro-5-(tetra-hydropyran-2-yloxy)furan (35). cis-Hydroxylation of the double bond in 35 was effected with potassium permanganate, yielding the ethyl DL-ribofuranoside derivative 36, which was hydrolyzed to DL-ribose. 

Stereospecific syntheses of the 1,1-diethyl acetals 45 and 47 were performed by Makin and coworkers.29 trans-5,5-Diethoxy-2-penten-l-ol (44) was cis-hydroxylated with potassium permanganate, to yield the diethyl acetal (45) of 2-deoxy-DL-threo-pentose. Epoxidation of 44 and alkaline hydrolysis of the epoxide 46 gave the diethyl acetal (47) of 2-deoxy-DL-en/thro-pentose. 

Pentenal was employed30 for an effective synthesis of the 2,3-di-deoxy-DL-pentose (50a). The aldehyde was converted into the dimethyl acetal 48 this was ci.s-hydroxylated with potassium permanganate to give diol 49. Mild, acid hydrolysis of 49 afforded the methyl... 

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