Thick-layer chromatography

The submitters also tried to purify the crude product by distillation (130-145° at 0.005 mm.), but under these conditions decomposition took place. It is possible to substitute thick-layer chromatography for the dry column. Using Merck silica gel F254 precoated plates, layer thickness 2 mm., and developing with 10 1 (vjv) benzene-acetone, the submitters report a 73% yield of pure product. 

A solution of dihydroergotamine (254) methanesulphonate in water was left in the sunlight for 15 days. The only photolysis product found was the derivative (255). There had been no alcohol in the reaction solution, so the molecule was assumed to have formed an oxo-derivative which gave the enol ether during separation by thick-layer chromatography [158], (Scheme 2.6). 

The technique of paper chromatography has been almost entirely superseded by thin- or thick-layer chromatography (see below). 

Phosphonium salts, which are generally stable in the form of iodide and tetraphenyl-borate crystalline solids, are frequently purified by recrystallization. Where this is not possible, thick-layer chromatography (0.2-1 mm Kieselguhr, silica) may afford a satisfactory method of purification12,13. In this manner, analysis using secondary ion mass spectrometry (SIMS) has a detection limit 10-50 ng per spot14. 

A mixture of the 2,4-dimethyl-5-methoxyoxazole (5 mmol) and the benzaldehyde (5 mmol) was dissolved in 50 mL benzene, the solution transferred to a vacuum-jacket quartz tube and degassed with a steady stream of N2 gas (Sch. 59). The reaction mixture was irradicated at 10 °C in a Rayonet photoreactor (RPR-208, 2 = 300 10 nm) for 24 h. The solvent was evaporated (40 °C, 20Torr) and the crude product was purified by preparative thick-layer chromatography (EA H= 1 4) to give 0.59 g (72%) of the oxetane 169 as a colorless oil. To a solution this photoproduct (2 mmol) in 20 mL methylene chloride, 0.5 mL of cone. HC1 was added. The mixture is stirred in an open flask at room temperature for 2h and the... 

This satisfactory analytical separation provided the data for scale up to a preparative separation. It was decided to obtain 200 mg of each amide from a 600-mg mixture of the b-, e-, and f-amides previously separated by thick-layer chromatography. When the cobester reaction mixture was separated using LC, seven other compounds were found, each comprising 2% or less of the reaction mixture. 

The reagent was used tu transform the ketodiene (1) in to the sesquiterpene oeeidenlalol (5). Thus a Wadsworth-Emmons reaction of (1) with diethyl l-(methylthio)ethyl-phosphonatc i cq.) in HMPT dimcthoxycthanc (62°, 12 hr.) gave the vinyl thiocthcr (2). This was hydrolyzed with mercuric chloride in aqueous acetonitrile to a 2.9 1 mixture of the 7a- and 7 -acetyl dienes (3) and (4), respectively, in 70% yield. The epimers were separated by preparative thick-layer chromatography. ( )-Oeeidenlalol (5) was obtained by addition of methyllithium to the 7a-isomer (3) (72% yield). 

To a stirred solution of 2-naphthol (0.14 g, 1.0 mmol) in benzene or THE (5 ml) was added tetramethyl-2-rerr-butylguanidine (0.21 g, 1.3 mmol) at room temperature under an inert atmosphere. Triphenylbismuth bis(trifluoroacetate) (0.80 g, 1.2 mmol) was added and the resulting mixture is stirred for an appropriate time. Then the solvent was evaporated and the residue is fractionated by thick layer chromatography using ether-hexane (1 4) as the eluent to give 1-phenyl-2-naphthol in 0.15 g, 70% yield. In some cases, triphenylbismuthine was also isolated [85 JCS(P1)2657]. 

A solution of acetylacetone (0.15 g, 1.5 mmol) in anhydrous benzene or dichloromethane (7.5 ml) was stirred under argon in the presence of triphenylbismuth carbonate (1.9 g, 3.8 mmol) until the reaction is complete. The reaction mixture was filtered though Celite, the filtrate was evaporated, and the residue was purified by preparative thick layer chromatography or column chromatography to give 3-phenylpentane-2,4-dione (0.10 g, 38% yield) and 3,3-diphenylpen-tane-2,4-dione (0.15 g, 40% yield) [85JCS(P1)2667]. 

Acomtum forreslii Diterpene alkaloid Forestine (36) Pelletier et at, (1984) Alumina, PF254 Thick Layer Chromatography (20cm X 20cm x 3mm) MCjCO Hexane (45 55) OH T. OMc El -N K OMc OH > OMe McO... 

A 2.0 g 3-methylfurfuryl benzoate (9.25 mmol) was flash vacuum pyrolyzed at 630°C in the normal manner. A quantitative NMR analysis of the pyrolysate indicated the presence of 3-methyl-4-methylenecyclobutenone in a 21% yield and its dimmer in a 24% yield. Thick layer chromatography on silica gel plates (2000 /j.) using two elutions with 20% EtOAc in hexanes afforded two major bands. The upper band consisted of 0.313 g 4H,5H,9H, 10H-cycloocta[l,2-b 6,5-t> ]difuran, in a yield of 18%, m.p. 49-52°C. The lower band was concentrated to give 0.139 g 3-methyl-4-methylenecyclobutenone, in a yield of 16%. 

A solution of 1-bromonaphthalene (0.70 ml, 5 mmol) in dry THF (2 ml) was cooled to -78 °C, and sec-BuLi (3.8 ml, 5 mmol, 1.3 M solution in cyclohexane) was added. The yellow heterogeneous mixture was stirred for 1 h at -78 °C, and then was warmed to -42 °C. To the yellow solution of 609, a solution of chiral oxazoline 602 (0.105 g, 0.28 mmol) in dry THF (4 ml) was added, and the resulting reaction mixture was stirred at -42 °C for 1 h. To this was added a saturated aqueous NH4CI solution (5 ml), and the mixture was warmed to 25 °C. The aqueous phase was neutralized vwth 10% HCl and washed with diethyl ether. The organic phases were combined, washed with water and brine, dried (MgS04), and concentrated. Thick layer chromatography on silica gel with... 

N-Iodoacetyl-3,B-dimethoxy-4-hydroxyphenylethylamine (Sa). To a solution of 3,5-dimethoxy-4-hydroxyphenylethylamine (4a, 0.245 g, 1.24 mmoles) and fV,i r -dicyclohexylcarbodiimide (DCC) (0.256 g, 1.24 mmoles) in 150 ml of dry acetonitrile is added 0.231 g (1.24 mmoles) of iodoacetic acid. The reaction mixture is stirred for 72 hr at ambient temperature, after which the solution is filtered and the solvent is removed under reduced pressure. The residue is applied to a silica gel thick-layer chromatography plate [1000 fim solvent system ethanol/ chloroform (1 9)]. The desired product is extracted from the developed silica gel plate with ethyl acetate. The ethyl acetate solution is filtered and the filtrate is concentrated under reduced pressure. The residual oil can be crystallized from chloroform and hexane. Yield, 0.19 g (42%) m.p. 122°-123.5°. 

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