Pyridine 1-oxides hydroxy

The 17a-hydroxy-etianic acid (294) forms an acetonide [ dioxolone (295)] under catalysis by perchloric acid. " The same dioxolone was formed by oxidation of the triol-acetonide (296) with chromium trioxide-pyridine. The hydroxy-acid (297) also forms a dioxolone. These derivatives are hydrolysed by alkali, but... 

HC(44/3)l>. The two most important methods are (i) conversion of thienyllithium to a thienyl-boronic acid by reaction with alkyl borate, followed by oxidation with H2O2, and (ii) reaction of thienylmagnesium derivatives with t-butylperbenzoate, followed by dealkylation of the /-butyl ethers with acid. The boronic acid method has been used for the synthesis of several pyridine-substituted hydroxy thiophenes <92ACS654>. 

Among other pyridine derivatives 2-hydroxy-pyridine-AT-oxides, 2-mercapto-pyridine- -oxides and 8-hydroxyquinolines are described in this section which may be looked at as membrane-active microbicides with chelating properties. The following pyridine compounds with antimicrobial activity but without significant importance for the protection of materials shall only be mentioned ... 

In peptide syntheses, where partial racemization of the chiral a-carbon centers is a serious problem, the application of 1-hydroxy-1 H-benzotriazole ( HBT") and DCC has been very successful in increasing yields and decreasing racemization (W. Kdnig, 1970 G.C. Windridge, 1971 H.R. Bosshard, 1973), l-(Acyloxy)-lif-benzotriazoles or l-acyl-17f-benzo-triazole 3-oxides are formed as reactive intermediates. If carboxylic or phosphoric esters are to be formed from the acids and alcohols using DCC, 4-(pyrrolidin-l -yl)pyridine ( PPY A. Hassner, 1978 K.M. Patel, 1979) and HBT are efficient catalysts even with tert-alkyl, choles-teryl, aryl, and other unreactive alcohols as well as with highly bulky or labile acids. 

Ethers of benzenepentol have been obtained by Dakin oxidation of the appropriately substituted acetophenone. Thus, the oxidation of 2-hydroxy-3,4,6-ttimethoxyacetophenone and 2-hydroxy-3,4,5-ttimethoxyacetophenone with hydrogen peroxide ia the presence of alkali gives l,2-dihydroxy-3,4,6-ttimethoxybenzene and l,2-dihydroxy-3,4,5-ttimethoxybenzene, respectively further methylation of these ethers yields the pentamethyl ether of benzenepentol (mp 58—59 degC) (253). The one-step aromatization of myoinositol to produce esters of pentahydroxybenzene is achieved by treatment with carboxylic acid anhydrides ia DMSO and ia the presence of pyridine (254) (see Vitamins). 6-Alkyl- or... 

Pyridine 1-oxide, 4-hydroxy-2,6-dimethyl-kinetie data, 2, 197 (73JCS(P2)1065)... 

If homolytic reaction conditions (heat and nonpolar solvents) can be avoided and if the reaction is conducted in the presence of a weak base, lead tetraacetate is an efficient oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones. The yield of product is in many cases better than that obtained by oxidation with chromium trioxide. The reaction in pyridine is moderately slow the intial red pyridine complex turns to a yellow solution as the reaction progresses, the color change thus serving as an indicator. The method is surprisingly mild and free of side reactions. Thus 17a-ethinyl-17jS-hydroxy steroids are not attacked and 5a-hydroxy-3-ket-ones are not dehydrated. 

Osmium Tetroxide Oxidation of a A -Cyanopregnene 20-Cyano-21-hydroxy-5j5-pregn-17(20)-ene-3,l l-dione21-methyl ether (8 g) isdissolved in 100 ml of benzene and 8 ml of pyridine. After the addition of 9.6 g of osmium tetroxide, the reaction mixture is stoppered and allowed to stand at room temperature for 5 days. The mixture is stirred for 24 hr with 160 ml of chloroform, 200 ml of methanol and 280 ml of an aqueous solution... 

In a typical Knof procedure, 3jS-hydroxyandrost-5-en-17-one acetate is epoxidized with perbenzoic acid (or m-chloroperbenzoic acid ) to a mixture of 5a,6a- and 5)5,6)5-epoxides (75) in 99 % yield. Subsequent oxidation with aqueous chromium trioxide in methyl ethyl ketone affords the 5a-hydroxy-6-ketone (76) in 89% yield. Baeyer-Villiger oxidation of the hydroxy ketone (76) with perbenzoic acid (or w-chloroperbenzoic acid ) gives keto acid (77) in 96% yield as a complex with benzoic acid. The benzoic acid can be removed by sublimation or, more conveniently, by treating the complex with benzoyl chloride and pyridine to give the easily isolated )5-lactone (70) in 40% yield. As described in section III-A, pyrolysis of j5-lactone (70) affords A -B-norsteroid (71). Knof used this reaction sequence to prepare 3)5-hydroxy-B-norandrost-5-en-17-one acetate, B-noran-... 

The intermediacy of dipolar species such as 186 has been demonstrated by reaction of enamines with 2-hydroxy-1-aldehydes of the aromatic series (129). The enamine (113) reacts in benzene solution at room temperature with 2-hydroxy-1-naphthaldehyde to give the crystalline adduct (188) in 91 % yield. Oxidation with chromium trioxide-pyridine of 188 gave 189 with p elimination of the morpholine moiety. Palladium on charcoal dehydrogenation of 189 gave the known 1,2-benzoxanthone (129). 

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