Chromatography Irradiation

The conversion of II to IV was monitored by gas chromatography. Irradiation under identical conditions of a mechanically stirred nethylene chloride solution of II with P -RB gives the results shown in Figure 4. 

The irradiation of tetra-/-butylcyclopentadienone with 254 nm light at 77 K produced a tricyclopentanone which, upon extended irradiation, lost carbon monoxide. Tetra-f-butyltetrahedrane was formed. This derivative of the second fundamental hydrocarbon of molecular formula (CH), namely tetrahedrane, is stable at room temperature and could be isolated after chromatography on silica gel in crystalline form (G. Maier, 1978). 

The irradiation of 2-methoxytropone (A) leads to methyl 4-oxo-2-cyclopentenyl-acetate (D). The reaction can be followed by analytical gas chromatography and two intermediates are observed. These have the structures B and C. Indicate a mechanism by which each of the three successive reactions might occur. The first two steps are photochemical, while the third is probably an acid-catalyzed reaction which occurs under the photolysis conditions. 

With 2537 k-Light. 1 g (140) in 140 ml anhydrous dioxane is irradiated for 20 hr at room temperature with a Hanau NK 6/20 low-pressure mercury lamp placed in a central water-cooled quartz finger. 0.19 g of (141) crystallize from the crude reaction mixture as described above. Chromatography of the residual material on silica gel with benzene-ethyl acetate (4 1) gives 0.29 g of B-nortestosterone acetate [(142) 28.5 %] and starting material (140). 

The synthesis of 1 -benzothiepin 1 -oxide (23) can be achieved via complex formation with tricarbonyl iron, and quantitative oxidation of the coordination compound 22 with 3-chloroperoxy-benzoic acid. Subsequent irradiation at — 50 C provides 23, which crystallized as yellow needles after low-temperature (-40 C) chromatography, and was characterized by 1H NMR spectroscopy at — 30 C23 before loosing sulfur within one hour at 13°C to give naphthalene. 

Throughout the irradiation a steady stream of argon was bubbled through the photolysate which was maintained at 20 C. Excess MeOH was removed under reduced pressure and the residue separated by column chromatography (neutral alumina). 

However, if the azepine is C-monosubstituted, e.g. 14, or unsymmetrically substituted, then two isomeric 2-azabicycloheptadienes, e. g. 15 and 16, may result corresponding to electrocyclic ring closure involving C2-C5 or C4-C7 of the azepine ring. In practice, the ratio of the two isomers formed (which may be separated by vapor phase chromatography) varies with the position of the substituent.236 In contrast, irradiation of methyl 2,5-di-tm-butyl-l//-azepine-l-carboxylatein methanol yields only methyl 3,5-di-tert-bulyl-2-azabicycIo[3.2.0]hepta-3,6-diene-2-carboxylate (81 %).70... 

Method A A solution of the azidoquinoline (5 mmol) in 3M KOMe in MeOH (40 mL) and dioxane (40 mL) was irradiated under N2 using a water-cooled, 125-W medium-pressure Hg lamp until all the azide [as measured by the disappearance of u(N3) at 2120 cm" 1 or by TLC] had reacted (4-10h). The photolysate was left to stand at 20 C for 24h then neutralized cautiously by the addition of 4M IICI in MeOH. The solvent was removed under reduced pressure and the crude product was purified initially by column chromatography on alumina (Type H, toluene), then finally by crystallization (petroleum ether). 

Dibenz[c,/][1,2]oxazcpine-ll-carbonitrile isomerizes to the TV-oxide acridine-9-carbonitrile 10-oxide on heating in aprotic solvents. Attempted chromatography on silica gel or alumina columns gave a mixture of the oxepino[2,3-6]quinolinecarbonitrile 2, the oxoazepinoindolecarbo-nitrile 3 and the benzo[c]-2-aza-l,6-oxa[10]annulenecarbonitrile 4. Only these types of compounds were isolated when 2,7-dimethylacridine 10-oxide was irradiated.6... 

Methyl-1-phenylisoquinoline 2-oxide (l.OOg, 4.3 mmol) in acetone (200 mL) was irradiated with a Hanovia Q-700 medium-pressure Hg lamp until TLC showed that all starting material had been consumed. The solution was evaporated in vacuo, and the oily residue purified by preparative layer chromatography yield 0.485 g (48.5%) mp 73-75 C. 

An ice-cold solution of a 3-oxa-6-azatricvclo[3.2.0.02,4]hept-6-ene 1 (0.5-1.0 mmol) in MeCN (200 mL) was irradiated with a 30-W low-pressure Hg lamp for 10-125 min. The solvent was removed under reduced pressure and the residue was treated with active charcoal and hexane/i-Pr20. The mixture was filtered and the filtrate was evaporated under reduced pressure to leave the almost pure 1,4-oxazepines as orange oils, which showed vmal (neat) — 1660-1650 cm-L The products decomposed on attempted chromatography. 

A solution of K.OH (l.l2g, 20mmol) in MeOH (lOmL) was added dropwise over 30 min to a solution of 10a (3.5 g, 10 mmol) in MeOH (350 mL) under irradiation with a 400-W high-pressure Hg lamp with a Pyrex filter. After further irradiation for 1 h, the solution was evaporated under reduced pressure below 30 C, Et20 was added and the solution was washed with sat. brine and then dried (MgS04). Evaporation was followed by chromatography of the residue (alumina, hexane/Et20) yield 1.05 g (70%) red crystals mp 81-8.3 C (i-Pr20). 

A solution of a 3-azidopyridine4(0.5-1.0 g) in a mixture of MeOH (75 mL) and dioxane (75 mL) containing NaOMc (2.5-3.0 g, large excess) was irradiated under N2 with a 400-W high-pressure Hg lamp equipped with a Pyrex filter until TLC indicated that the reaction was complete (1 - 2 h). The solvents were removed under reduced pressure, the residue was treated with ice-water (10-20 mL) and the mixture was extracted with hexane. The extract was washed with H20, dried and evaporated in vacuo to leave the product, which was further purified by chromatography (Sephadex, benzene). All the diazepines were oils. 

A solution of the quinoxaline 1-oxide (4 mmol) in cyclohexane was degassed by boiling and passing N2 through and irradiated with a medium-pressure water-cooled Hg lamp (Hanau TQ 150), equipped with a Pyrex filter, until conversion was complete. The solvent was evaporated in vacuo at 20 C and the residue was extracted with a small amount of cyclohexane. The product was deposited on strong cooling. Attempted chromatography resulted in the formation of AfW-diacylbenzene-l,2-diamines. 

The irradiation of 4-azido-3-methoxypyridazine (I, R = H 0.5 g, 6.6 mmol) was carried out as described above, except that only 1 cquiv of NaOMe was used. After the mixture had been evaporated the residue was dissolved in ice-cold pyridine (3 4 mL), AcCl (0.4 g, 5.1 mmol) was added, the solution was stirred at 20 C for 5-6 h then poured into ice-water (20 mL). The mixture was extracted with CH2C12 and the extract was washed successively with sat. aq NaHCOj and H20 and dried. Evaporation, followed by chromatography of the residue (alumina, 9% Et20,/CH2CI2) gave the product yield 0.34 g (26%) pale-yellow plates (hexane) mp 112-113LC. 

A solution of phenol (188 mg, 2 mmol) and benzonitrile (2.06 g, 20 mmol) in McCN (20 mL) was degassed by bubbling nitrogen through it and irradiated with a 16-W low-pressure mercury arc lamp (Applied Photophysics Ltd, APQ40) for 24h. The crude product was separated by flash chromatography (EtOAc/ petroleum ether 1 5) to give yellow crystals yield 79 mg (20%) mp 53-55 C. 

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