Tetrahydrofuran solution, photolysis

Cyanophenyl azide is of interest in that on photolysis in methanol/tetrahydrofuran solution, an unseparated 1 1 mixture (by HNMR spectroscopy) of 2-methoxy-3//-azepine-3-carbonitrile and -7-carbonitrile (44%) is formed.197-282 Likewise, irradiation of 2-azidophenyl methyl ketone in methanol furnishes a mixture of 3-acetyl-2-methoxy- (11 %) and 7-acetyl-2-methoxy-3//-azcpine (3%) along with 3-methyl-2,l-benzisoxazole (18%).78... 

Attempts to effect ring expansion of methyl 2-azidobenzoate in the presence of other nucleophiles have failed. Thus, photolysis in tetrahydrofuran solution saturated with hydrogen sulfide, or with ammonia, produced methyl 2-aminobenzoate in 54 and 37 % yield, respectively, as the sole identifiable product.197 Photolysis of phenyl azide in ethanolic phenol gave 2-phenoxy-3//-azepine in poor yield (8 %).203,204 2-Mesityl-3//-azepine (10 %) is the surprising, and only tentatively explained, product from the photolysis of phenyl azide in mcsitylene in the presence of trifluoroacetic acid.179... 

In contrast, aryl azides 86 bearing an ortho electron-withdrawing group, particularly a carbonyl function, in methanol solution ring expand upon photolysis in practicable yields to provide 2-alkoxy-3//-azepines 87 36,74,195 -197 shorter reaction times and improved yields are often obtained using a 1 1 alcohol/tetrahydrofuran mixture. 

While still slightly warm from the drying oven, the photolysis vessel with a water-jacketed quartz immersion well (Note 1) (section A of Figure 2) is charged with 500 ml. of anhydrous tetrahydrofuran (Note 2) and 10 ml. (8.05 g., 0.122 mole) of cyclopentadiene (Note 3). The solution is cooled in an ice bath and purged with dry nitrogen for 2 minutes. Then the vessel is sealed, the lamp inserted, and the solution irradiated at 0° for 30 minutes. During this period, sections B and C... 

Dccalin (decahydronaphthalene),benzene, 1,4-dioxane, and ethanol may be used as solvents for the photolysis. In an alternative procedure, volatile materials swept from the photolysis vessel are condensed in a dry ice trap. This cold mixture is added to a flask containing a magnetically stirred solution of dimsyl anion in dimethyl sulfoxide, and fractionation at reduced pressure provides a solution of bicyclopentene in tetrahydrofuran. 

The addition of sodium to aromatic hydrocarbons produces only the corresponding radical anion [121]. Alkali metals, however, dissolve in aliphatic ethers, e.g. tetrahydrofuran, dioxan, producing the characteristic blue colour [122], The solutions are diamagnetic because of the formation of higher ion pairs. Flash photolysis of solutions of sodium in ethers forms the ion pair consisting of the solvated electron and a sodium cation [123]. Three transients are formed in the flash photolysis of sodium pyrenide in tetrahydrofuran [124]. These have been identified as the solvated electron, es"oiv. the ion pair, esoiv> Na, and the sodium atom, Na°. Rate coefficients of reactions of es ,iv with various compounds relative to the rate of reaction with NjO have been determined recently by the 7-radiolysis of 2-methyl-tetrahydrofuran [125]. 

Boron.—The principal reaction on photolysis of Na+[BPh4] in tetrahydrofuran or dimethoxyethane solution is formation of biphenyl and Na+[BPh2]-.466 This latter species exhibits carbenoid-like activity and reacts with diphenylacetylene to give an equilibrating mixture of (76) and (77). Radical formation on irradiation of MPh3 (M = , Al, or Ga) at 77 has been discussed.467... 

A fused oxaziridine has been trapped by matrix isolation in ethanol and in 2-methyl-tetrahydrofuran glasses at 77 K on photolysis of (84a) <80JA5643>. It has been suggested that this oxaziridine cleaves homolytically to a diradical on warming and the solution phase photochemistry, leading to (85a), involves this diradical intermediate formed directly from the AAoxide <88JCS(P2)235>. 

Beyond the few simple substitution reactions summarized below, the dominant chemistry reported for the fully-unsaturated diazocines (15) and (16) involves their thermal and photochemical ring contraction. Both the thermal and photochemical reactions appear to proceed via intermediate formation of bicyclo[4.2.0]octatriene valence tautomers. However, the product distribution differs considerably between the thermal and photochemical reactions. Thus, thermolysis of (15) in dode-cane solution at 140°C affords benzene (43.2%) and pyridine (56.8%) at 175°C, benzene becomes the major product (55.7% vs. 44.3% pyridine) (Scheme 3). Pyridazine, however, is not formed. In contrast, photolysis in tetrahydrofuran at >300 nm affords only benzene neither pyridine nor pyridazine are detected <79JOCl264>. 

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