Aryl, photolysis

Photolysis of Cp2TiAr2 in benzene solution yields titanocene and a variety of aryl products derived both intra- and intermolecularly (293—297). Dimethyl titan ocene photolyzed in hydrocarbons yields methane, but the hydrogen is derived from the other methyl group and from the cyclopentadienyl rings, as demonstrated by deuteration. Photolysis in the presence of diphenylacetylene yields the dimeric titanocycle (28) and a titanomethylation product [65090-11-1]. 

Direct proof of an oxaziridine intermediate was achieved in photolysis experiments in an organic glass at 77 K (80JA5643). Oxaziridine (75), formed by photolysis of A/-oxide (74) and evidenced by UV spectroscopy under the above conditions, decomposed at higher temperature to form the imino ether (76) by N—O bond cleavage and C -> O migration of an aryl group. 

The first benzazetidine (243) was isolated from the photolysis of 3-phenyldihydroben-zotriazine (242) (66JA1580). Another route to benzazetidines involving formation of the N to aryl-C bond utilizes intramolecular nucleophilic substitution via aryne (287). It is not general, however, and is only satisfactory when R and/or are alkoxy groups. The reaction also fails for iV-alkylamines (78LA608). 

Thiazole, 2-( D-galactopentaacetoxypentyl)-4-methyl-synthesis, 6, 295 Thiazole, 2-hydrazi nosynthesis, 6, 297 Thiazole, 2-hydroxy-reactions, 6, 285-286 synthesis, 6, 298, 299 tautomerism, 5, 99 6, 247, 269 Thiazole, 4-hydroxy-reactions, 5, 101 6, 287-288 synthesis, 6, 303 tautomerism, 6, 248, 269 Thiazole, 2-hydroxybenzyl-biosynthesis, 1, 96 Thiazole, 2-hydroxy-4-methyl-arylation, 6, 256 Thiazole, 2-iodo-photolysis, 6, 244 Thiazole, 2-isobutyl-occurrence, 6, 327... 

Aiyl esters, prepared from the phenol and an acid chloride or anhydride in the presence of base, are readily cleaved by saponification. In general they are more readily cleaved than the related esters of alcohols, thus allowing selective removal of phenolic esters. 9-Fluorenecarboxylates and 9-xanthenecarboxylates are also cleaved by photolysis. To permit selective removal, a number of carbonate esters have been investigated aryl benzyl carbonates can be cleaved by hydrogenolysis aryl 2,2,2-trichloroethyl carbonates, by Zn/THF-H20. 

Aryl 9-fluorenecarboxylates prepared from the phenol and the acid chloride (9-fluorenecaibonyl chloride, Pyr, C6H6, 25°, 1 h, 65% yield) can be cleaved by photolysis (hv, Et20 reflux, 4 h, 60% yield). The related aryl xanthenecarboxy-lates (i) were prepared and cleaved in the same way. ... 

Mixed aryl selenides have also proven to be excellent ree ents for group transfer reactions.Photolysis of selenides in an inert solvent such as benzene can initiate chain reactions. Substituted radicals can be generated in this manner, from a-selenoe-... 

Depending on structure, photolysis of films of arenediazonium fluoroborates and hexafluorophosphates at room temperature gives aryl fluorides m 10-75% yield [32] In situ photochemical decomposition of arenediazonium fluoroborates... 

Phenyl radicals can be generated by the thermal decomposition of lead tctrabcnzoate, phenyl iodosobenzoate, and diphenyliodonium hydroxide,- - and by the electrolysis of benzoic acid.- These methods have been employed in the arylation of aromatic compounds, including heterocycles. A method of promise which has not been applied to the arylation of heterocycles is the formation of aryl radicals by the photolysis of aromatic iodides at 2537... 

Ring expansion of the benzene ring of a calix[6]arene to a 1 //-azepine in 14% yield by photolysis of an aryl azide confined in the calix structure has been reported.294... 

The synthesis of 3//-azepines by the photolysis of aryl azides in nucleophilic media is a much more efficient and versatile route than the thermolytic process. Initial studies involved photolysis of the aryl azides in an excess of a secondary aliphatic amine, and moderate yields of A, V-dialkyl-3//-azepin-2-amines 38 were obtained.35-1 72... 

Photolysis of aryl azides in amine solution, with a tertiary amine as cosolvent to promote stabilization of the singlet nitrene, has met with some success. For example, the yield of 2-piperidino-3 W-azepme. obtained by the photolysis of phenyl azide in piperidine, is increased from 35 to 58% in the presence of A A /V. /V -tetramethylethylenediamine (TMLDA).180 Also, an improved yield (36 to 60 %) of A,(V-diethyl-3W-azepin-2-amine (38, R = Et) can be obtained by irradiating phenyl azide in triethylamine, rather than in dicthylaminc, solution.181 Photolysis (or thermolysis) of phenyl azide in TMEDA produces, in each case, 38 (R = Et) in 40% yield.181 In contrast, irradiation of phenyl azide in aniline with trimethylamine as cosolvent furnishes jV-phenyl-377-azepin-2-amine (32, R = Ph) in only low yield (2%).35... 

As expected of an unsymmetrically substituted aryl azide, the photolysis of 5-azidoindane (68) in diethylamine furnishes an unseparated mixture (31 % yield) of /V./V-diethyl-l, 6,7,8-tetrahyd-rocyclopent[J]azepin-2-aminc (69) and /Y,/V-diethyl-4,6,7,8-tctrahydrocyclopent[[Pg.151]

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. 

Practicable yields of 5-substituted 2-methoxy-3//-azepines 94 can be obtained by photolysis of aryl azides 56 bearing an electron-withdrawing group para to the azide function, although irradiation times tend to be longer and, in general, yields lower than with the corresponding 2-substituted azides.197... 

The photolysis of aryl azides in water or aqueous tetrahydrofuran provides access to 1 //-azepin-2(37/)-ones. 136.197.199.202... 

Nucleophilic displacement of the butoxy group in 2-butoxy-3//-azepine (1) by the use of excess secondary amine is preferred by some workers64 to the photolysis or thermolysis of aryl azides, or the deoxygenation of nitro- or nitrosoarenes in amine solution, as a preparative route to Ar,Ar-dialkyl-3//-azcpin-2-amines, e.g. 2,... 

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