Hydroxy-, derivatives with peracids

Oxidation of thiophene with peracid under carefully controlled conditions gives a mixture of thiophene sulfoxide and 2-hydroxythiophene sulfoxide. These compounds are trapped by addition to benzoquinone to give ultimately naphthoquinone (225) and its 5-hydroxy derivative (226) (76ACS(B)353). The further oxidation of the sulfoxide yields the sulfone, which may function as a diene or dienophile in the Diels-Alder reaction (Scheme 88). An azulene synthesis involves the addition of 6-(A,A-dimethylamino)fulvene (227) to a thiophene sulfone (77TL639, 77JA4199). 

Alkyl-1,4-dihydropyridines on reaction with peracids undergo either extensive decomposition or biomimetic oxidation to A-alkylpyridinum salts (98JOC10001). However, A-methoxycarbonyl derivatives of 1,4- and 1,2-dihydro-pyridines (74) and (8a) react with m-CPBA to give the methyl tmns-2- 2>-chlorobenzoyloxy)-3-hydroxy-1,2,3,4-tetrahydropyridine-l-carboxylate (75) and methyl rran.s-2-(3-chlorobenzoyloxy)-3-hydroxy-l,2,3,6-tetrahydropyridine-l-carboxylate (76) in 65% and 66% yield, respectively (nonbiomimetic oxidation). The reaction is related to the interaction of peracids with enol ethers and involves the initial formation of an aminoepoxide, which is opened in situ by m-chlorobenzoic acid regio- and stereoselectively (57JA3234, 93JA7593). 

Treatment of a P-keto ester direedy with peracid has been shown in one case (Itf to effect quantitative a-hydroxylation. Presumably this arises through epoxidation of the enol. Peracid reactions of this kind will be discussed in more detail in Section 2.3.2.1.3.i. Oxidations of the enols of P-keti> esters to the a-hydroxy derivatives using singlet oxygen in the presence of fluoride ion occurs in moderate yield through an ene process (Section 2.3.2.1.3.ii). 

Enamines are susceptible to peracid oxidation, presumably through the epoxide, producing the a-hy-droxy ketone after hy lysis. Thus steroidal ketone (88) is converted via the pyrollidino enamine to the a-hydroxy derivative (89) in qiproximately 50% overall yield by treatment of the enamine with MCPBA followed by basic work up. Similar conversion of a steroidal enamide to the a>hydroxy ketone using monoperphthalic acid has been reported. 

These derivatives of carboxylic acids behave analogously to ester silyl ketene acetals (Section 2.3.2.4.3.i). Thus treatment with peracid in hexane followed by acidic work-up allows isolation of good yields of the a-hydroxy acids. 

The proportions of a- and /8-epoxides obtained by peracid reactions of cholest-4-ene and its 7a- and 7/3-hydroxy-, 7/8-acetoxy-, and 7-oxo-derivatives have been compared with data for similar 3-substituted cholest-5-enes. The derived 4a,5a-and 5a,6a-epoxides all reacted smoothly with sodium azide to give azido-alcohols, with maximum reaction rates when a hydroxy-group was suitably placed to provide... 

Electrophilic Addition.—Reactions of androsta-3,5-dienes with MCPBA gave complex mixtures the composition of which was dependent upon the level of peracid used (1 or 2 equivalents). Diepoxides were isolated in low yield only when 2 equivalents were used and in general products were derived from epoxide ring opening.34 In a study of the structures of withanolides G,H,I,J,K, and U which were all shown to possess the 14a-hydroxy-group, it was demonstrated that the 14a-hydroxy-group influenced the epoxidation of the 5,6-double bond.35 Incorporation of ozonizable dyes as internal standards facilitated selective ozonization of... 

The Rubottom oxidation1 is the peracid-mediated oxidation of trimethylsilyl enol ethers to afford a-silyloxy- or a-hydroxy aldehydes or ketones.2,3 Use of an aqueous workup generally affords the hydroxy compounds, whereas nonaqueous workups provide the silyloxy derivatives. For example, the enolsilane 1 derived from cycloheptanone was converted to 2 in 77% yield by treatment with /w-CPBA followed by workup with 10% aqueous sodium hydroxide. Omission of the aqueous workup afforded 3 in 85% isolated yield,1 ... 

Balthazor and coworkers reported the synthesis of l,3-dihydro-l-hydroxy-3-methyl-l,2,3-benzio-doxaphosphole 2-oxide (95) by the peracetic oxidation of 2-iodophenylmethylphosphinic acid (201) (Scheme 2.63) [247]. Benziodoxaphosphole 95 can be converted into the methoxy derivative 202 by treatment with hot methanol. Methoxybenziodoxaphosphole 202 is readily hydrolyzed in moist air to give the initial hydroxyben-ziodoxaphosphole 201 [247]. Freedman and DeMott reported a similar preparation of benziodoxaphospholes 203 and 204 by a peracid oxidation of 2-iodophenylphosphonic acid or (2-iodophenyl)phenylphosphinic acid, respectively [334]. 

Peroxides are usually used to oxidize aldehydes to aryl formates. In the case of hydroxy aldehydes, hydrogen peroxide under basic conditions is the most suitable oxidant [175]. With benzaldehydes and aromatic aldehydes bearing alkoxy groups, use of hydrogen peroxide catalyzed by selenium derivatives [176] or performance of the reaction under acidic conditions [177] gives better results. Peracids, and in particular... 

The oxidation of 8-hydroxy-5-methyldihydrothiazolo[3,2-a]pyridinium-3-carboxylate by a variety of oxidizing agents produces the ds-sulphoxide, precisely as previously outlined for the action of peracids (see these Reports, Vol. 1, p. 432). The corresponding 2-carboxyIate (210) yields, in this reaction, the thiazole (212) by loss of water from (211), as well as minor products formed by fission of the thiazole ring. Oxidation of the trans-2,6-dicarboxy-derivative corresponding to (210) yields the same thiazole (212) with simultaneous decarboxylation. ... 

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