ELBS Oxidation

Also known as the Elbs persulfate oxidation,it is a variant of the Boyland-Sims oxidation except the substrate is phenol rather than aniline. Its mechanism is similar to that of the Boyland-Sims oxidation. 

Boyland, E. Manson, D. Sims, P. J. Chem. Soc. 1953, 3623-3628. Eric Boyland and Peter Sims were at the Royal Cancer Hospital in London, UK. 

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Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

Hydroxypyridine and pyridin-2-one are sufficiently reactive to undergo Elbs oxidation, and in both cases the substituent directs hydroxylation mainly para (Scheme 40) (58JA3717). Quinoline may be converted into 3-hydroxyquinoline (6% yield) by Udenfriend oxidation (ascorbic acid and oxygen in the presence of iron(II)) which is believed to involve attack by OH+ rather than radicals (54JBC(208)74i). 

Hydroxylation of arylamines with persulfate ion, or Boyland-Sims oxidation, gives ortho-substituted aminophenols in good yields [29]. As with the Elbs oxidation, the procedure is also carried out in two steps - first, treatment with the oxidant to obtain an aminophenyl sulfate ester and, second, hydrolysis to obtain the final product. Primary, secondary and tertiary amines can all be used in this reaction. The ortho product is formed, except when no ortho-positions are available, which leads to para-substitution. Electrophilic attack on the ipso-carbon is believed to be the most likely mechanism, although minor radical pathways also seem to be present. 

Elbs oxidation of phenolic precursors gave quinones 319 and 320. These are transformed in the presence of alkali into 319 (66CPB121), which was also obtained in low yield from the aminohydroxy precursor by nitrous oxidation (64CPB307). 

Persulfate Replacement of hydrogen by hydroxyl Elbs oxidation s. 1,131 SgOg- H —OH... 

Elbs oxidation (1, 952), The Elbs oxidation is a key step in a recent regio-specific synthesis of islandicin monomethyl ether (3), a possible precursor to anthracycline antibiotics (equation I). ... 

Pyridone is another six-membered ring heterocycle, and it was converted to 5-hydroxy-2-piperidone 2.167) by an Elbs oxidation.80 Catalytic hydrogenation converted the pyridone ring to a lactam 2.168) and acid hydrolysis gave 5-amino-4-oxopentanoic acid, 2.169 ... 

A novel regiospecific synthesis of islandicin was described by Glein etal. 145) (Scheme 21). Thus Fries rearrangement of l-propionyloxy-5-methoxynaphthalene followed by methylation and bromination yielded the ketone (172). Alkylation with sodium diethyl malonate followed by demethylation, ester hydrolysis and decarboxylation gave the acid (173). Elbs oxidation and sulfuric acid cyclisation of the acid yielded 1-O-methyl-islandicin (174). 

Elbs oxidation of 2- and 3-hydroxypyridine gives in each case mainly 2,5-dihydroxypyridine. In the first case some 2,3-dihydroxypyridine, and in the second, some 2,3- and 3,4-dihydroxypyridine are also formed. The kinetics and mechanism of the oxidation of 2-hydroxypyridine have been examined, and the reaction could involve attack by the anion of the hydroxy compound upon the peroxy bond of the persulphate ion, with the displacement of sulphate ioni sa, 2-Aminopyridine gives hydrogen 2-amino-3-pyridyl sulphate but 4-aminopyridine behaves differently (p. 359). 

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