Methyl ethers chromatography

After stirring for 1 hr more, the reaction mixture is diluted with 500 ml of cold water the yellow precipitate which forms is filtered, washed and dried, to give 4.1 g (83%) of crude 16-diazoestrone methyl ether (94) mp 133-136°. Chromatography of the crude product over neutral alumina in chloroform, followed by recrystallization from chloroform-methanol, gives pure (94) mp 145-146°, in 64% over-all yield. ... 

Likewise, synthetic 2//-azepines isomerize to 3//-azepines in refluxing chloroform (2-3 h) or in tert-butyl methyl ether at room temperature.291 The isomers can be readily separated by chromatography on silica gel, as the more basic 2//-azepines30 have lower Rf values. In contrast, 7-butyl-2//-azepin-2-acetic acid (11), obtained by heating the tert-butyl ester 10 with iodotrimethylsilane, is stabilized by intramolecular hydrogen bonding and shows no tendency to rearrange to the 3//-isomer.291... 

A solution of 1-trimethylsilyloxycyclohex-l-ene (5.12 mmol) and benzaldehyde dimethyl acetal (5.47 mmol) in dichloromethane (15 ml) was cooled to —78°C, and to this was added TMSOTf (0.05 mmol) in dichloromethane (0.5 ml). The mixture was stirred at -78°C for 8h, and then quenched by the addition of water at —78 °C. Dichloromethane (50 ml) was added, and the mixture was washed with saturated sodium hydrogen carbonate solution and brine, and dried. Concentration provided a crude oil consisting of a 93 7 mixture of erythro- and r/jreo-2-(methoxyphenyl-methyl)cyclohexanone. Chromatography on silica gel (20g, eluant petroleum ether ether 10 1) gave the pure erythro (82%) and threo (6.7%) isomers as oils. 

Substitution of methanol for ethanol gave a mixture that was inseparable by column chromatography. The new compound in the mixture exhibited a singlet as expected for the methyl ether. 

The crude product was purified by column chromatography (n-pentane t-butyl methyl ether dichloromethane 5 4 1) yielding l,l -di(benzoyl)ferro-cene (16.16g, 41.0mmol, 82%) as a dark red solid (mp 97-100°C). 

Renberg [35] used an ion-exchange technique for the determination of chlorophenols and phenoxy acetic acid herbicides in soil. In this method the soil extracts are mixed with Sephadex QAE A-25 anion exchanger and the adsorbed materials are then eluted with a suitable solvent. The chlorinated phenols are converted into their methyl ethers and the chlorinated phenoxy acids into their methyl or 2-chloroethyl esters for gas chromatography. 

The last synthesis to evolve which is due to Ito and his coworkers is interesting in that it relies on a stereospecific skeletal rearrangement of a bicyclo[2.2.2]octane system which in turn was prepared by Diels-Alder methodology (Scheme XLVIII) Heating of a toluene solution of cyclopentene 1,2-dicarboxylic anhydride and 4-methylcyclohexa-l,4-dienyl methyl ether in the presence of a catalytic quantity of p-toluenesulfonic acid afforded 589. Demethylation was followed by reduction and cyclization to sulfide 590. Desulfurization set the stage for peracid oxidation and arrival at 591. Chromatography of this intermediate on alumina induced isomerization to keto alcohol 592. Jones oxidation afforded diketone 593 which had earlier been transformed into gymnomitrol. 

Each fraction was monitored by thin-layer chromatography on silica gel (Merck Silica Gel 60 F-254). The Rf values (dichloromethane) of the product and starting estrone 3-methyl ether are 0.53 and 0.40, respectively. 

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