Pyridinium glycols

The well-known triphenyltetrazolium chloride (TTC) reaction for the detection of a-ketolsteroids, pyridinium carbinols and pyridinium glycols can also be included here [20-23]. The chromophore system of the red-colored formazan dye produced by reduction of the TTC is composed of highly conjugated double bonds resulting from the combination of a phenylhydrazone group with an azo group ... 

Purpuric acid lb 174 Pyrazolidine derivatives la 426 3,5-Pyrazolidindione derivatives lb 20 Pyrazolinone derivatives lb 277 Pyrazolin-5-one derivatives lb 327,329 Pyrazone lb 332 Pyrene lb 379 PyrethrinI lb 18 Pyrethrin II lb 18 Pyrethroids lb 86,87 Pyrethroid insecticides la 359 Pyridine alkaloids la 66 lb 279 Pyridine derivatives lb 119,244 Pyridinium carbinols lb 65 Pyridinium glycols lb 65 Pyridoxal la 157,158,253 Pyridoxamine la 253 Pyridoxine la 253... 

Acetoxyandrost-5-en-17-one (59) is converted into the ethylene ketal (60) by treatment with ethylene glycol, triethylorthoformate and p-toluenesulfonic acid. The ketal is brominated with pyridinium bromide perbromide in THF and then treated with sodium iodide to remove bromine from the 5 and 6 positions. This gives the 16a-bromo compound (61) which is hydrolyzed in methanol to the free alcohol (62). Dehydrobromination is effected with potassium Fbutoxide in DMSO to give the -compound (63). Acid catalyzed hydrolysis of the ketal in aqueous acetone gives the title compound (64). ... 

N-Methyl-2-pyrrolidinone 2 KHSO5 KHSO4 K2SO4 Polymeric backbone Pyridinium chlorochromate Pyridinium dichromate Polyethylene glycol... 

Pyridinium chlorochromate Pyridinium dichromate Polyethylene glycol... 

A library of 1,2,3,7-tetrasubstituted indolizines was synthesized using poly(ethylene glycol) (PEG) bound pyridinium salts reacting with alkenes or alkynes in the presence of Et3N <2006JHC781>. 

The utilization of polar polymers and novel N-alkyl-4-(N, N -dialklamino)pyridinium sedts as stable phase transfer catalysts for nucleophilic aromatic substitution are reported. Polar polymers such as poly (ethylene glycol) or polyvinylpyrrolidone are thermally stable, but provide only slow rates. The dialkylaminopyridininium salts are very active catalysts, and are up to 100 times more stable than tetrabutylammonium bromide, allowing recovery and reuse of catalyst. The utilization of b is-dialkylaminopypridinium salts for phase-transfer catalyzed nucleophilic substitution by bisphenoxides leads to enhanced rates, and the requirement of less catalyst. Experimental details are provided. 

Chabardes developed a process for the preparation of vitamin A and its intermediates, from cyclogeranylsulfone and Cio aldehyde-acetals [30]. For example, chlorocitral reacted with ethylene glycol, HC(OMe)3 and pyridinium tosylate to provide the chloroacetal (40%), as a mixture of two isomers. Reaction of this allylchloride with A-methylmorpholine oxide (NMO) and Nal furnished the aldehyde, as a mixture of four isomers. These compounds underwent condensation with P-cyclogeranylsulfone. Further chlorination of the sulfone-alkoxide salts, led to a mixture of sulfone-chloride acetals and their products of hydrolysis in 45-50% yield. Double elimination of the chloride and the sulfone, followed by hydrolysis with pyridinium tosylate (PPTS) gave retinal, as a mixture of all E and 13Z isomers (78/22). The overall yield from the chloroacetal was 18%. In another one-pot example, retinal was obtained in 52% yield from the aldehyde, and was then isomerised and reduced to retinol (all E 95.5, 13Z 4, 9Z 0.5) Fig. (8). 

Different reactivities of some substituted oxan-4-ols on oxidation by pyridinium chlorochromate (PCC) are rationalized on the basis of their conformational features, including twist conformations.2 A rate-determining carbon-carbon bond cleavage step in a glycol-PCC complex is proposed in the oxidation of butane-2,3-diol to acetaldehyde.3 Steroidal 6/i-hydroxy-4-en-3-onc was isolated as an intermediate in the oxidation of steroidal 5-en-3/i-ol with PCC.4... 

D KIE of 6.35 has been observed in the oxidation of a-deuteriomandelic acid by pyri-dinium bromochromate to the corresponding oxo acid. The analysis of the D KIE indicated that the reaction involves a symmetric transition state443. The oxidations of phosphinic and phosphorous acids by pyridinium bromochromate exhibits a substantial primary deuterium KIE444. The hydroxyacids, glycolic, lactic, mandelic and malic acids are oxidized by pyridinium hydrobromide perbromide in acetic acid-water mixtures to oxo acids445. The primary KIE in the oxidation of a-deuteriomandelic acid is kn/kn = 5.07, and it does not exhibit a solvent isotope effect. A mechanism involving hydride ion transfer to the oxidant has been proposed445. 

Oxidation of glycol esters to ene-S-lactones. Reaction of glycal esters with m-chloroperbenzoic acid involves the expected epoxidation followed by cleavage of the oxide by the /n-chlorobenzoic acid formed. However, in the presence of BF3, the reaction produces a,/ -unsaturated 5-lactones, usually in excellent yield. This oxidation is also possible with pyridinium chlorochromate and BF3 as catalyst, but in lower yield.1... 

Heller [3] prepared bioerodible block copolymers using pyridinium p-toluenesulfonate consisting of ortho esters and ethylene glycol, (II), end-capped with triethylene glycol monoglycolide. 

Selective enone ketalization. The reaction of ethylene glycol catalyzed by pyri-dinium p-toluenesulfonate (PPTS) does not discriminate between saturated and a, 3-unsaturated ketones. In contrast, this hindered pyridinium salt (1) permits selective ketalization of enones in the presence of saturated keto groups. 2,6-Lutidinium p-toluenesulfonate (2) is as effective. 

A solution of the ketone (1.23 g, 8.11 mmol), ethylene glycol (1.8 mL, 32 mmol), pyridinium tosylate (0.6 g, 2.4 mmol), and benzene (45 mL) was refluxed for 22 h in a Dean-Stark apparatus. The reaction mixture was cooled, poured into saturated NaHCOj (50 mL), the aqueous layer extracted with hexanes/EtiO (1/1, 2 x 20 mL), and washed with brine (2 x 15 mL). The combined organics were dried (MgSO4), concentrated, and chromatographed to give the ketal (1.59 g, 100%). 

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