62-Isoxazoline, photolysis

An extensive and a systematic photochemical studies had been done on 2-isoxazoline. Photolysis of 2-isoxazolines always result in a mixture of products, depending upon the nature of the substituents. Three possible different pathways of photolytic cleavage are reviewed <9iHC(49)l>. Ultraviolet irradiation of 5-unsubstituted 2-isoxazoline (127) in the presence of iron pentacarbonyl, resulted in ring fragmentation products (a ketone (128) and aldehyde (129)) as well as N—O bond fission products ((130) and (131)) (Scheme 21). The plausible mechanism involves N-donor complexation with photochemically generated pentacarbonyl, prior to N—O and C(3)—C(4) bond fissions <83CL51>. 

The photolysis of 4-substituted 2,3-dimethyl-3-isoxazolin-5-ones has been studied. Irradiation in methanol or ethanol with a 100 W high-pressure mercury lamp through a Pyrex filter of a 4-phenylthio compound produced a semithioacetal (Scheme 5). In contrast, an H, Cl or OPh moiety gave no reaction. The use of alkylthio substitution gave similar products. Cyclic compounds yielded cyclic products (Scheme 5), and the photolysis of (29) in benzene... 

The photolysis of 3-( p-cyanophenyl)-2-isoxazoline in benzene produced a tricyclic product along with six other materials (Scheme 46) (B-79MI41616). Irradiation of the bicyclic 2-isoxazoline (155) produced benzonitrile, /3-cyanonaphthalene and polymer via a proposed biradical intermediate (156) (Scheme 47) (B-79MI41615). 

Acetonitrile oxide was generated from 3,4-dimethylfuroxan oxide by flash vacuum pyrolysis and trapped at -40 °C where its and NMR spectra were examined. Warming to room temperature in the presence of propane produced 3,5-dimethyl-2-isoxazoline (Scheme 108) (79TL2443). The oxide could also be generated by photolysis of furoxan (68CC977). 

Jurd reported the isolation of a 2//-3-isoxazoline by the reaction of the flavylium salt (488) with hydroxylamine. Gentle heating of the material caused isomerization to the more stable 2-isoxazoline. Treatment with base generated an a,/3-unsaturated oxime which on photolysis regenerated the starting flavylium salt (Scheme 129) (70CI(L)624). 

Cyclopropenones react with nitrosobenzene by an O-initiated attack at C-1 to produce isoxazolin-5-ones (75TL3283, 78USP4053481), and an isoxazolin-5-one was produced as a by-product in the photolysis of nitroethylene (78AJCU3). Substituted oxazolin-5-ones have... 

Bis(isoxazoline) decomposes to a number of products depending on the substitution (77H(6)1599) On photolysis using NiS04, two major products were formed. ESR spin trapping demonstrated the intermediacy of imino and 2-isoxazolinyl radicals (77TL4619). 

Isoxazolines bromination, 6, 78 chemical potentials, 6, 7 melting and boiling points, 6, 9 oxidation, 6, 37 photolysis, 6, 37-38 N-oxides... 

Isoxazolin-5-imine, 2,3,4-triphenyl-photolysis, 6, 43 Isoxazolin-5-imines synthesis, 6, 105 2-Isoxazolin-5-ol synthesis, 6, 100 Isoxazolinols synthesis, 6, 100-102 Isoxazolin-3-one, 5-methyl-2-phenyl-rearrangement, 6, 43 Isoxazolin-5-one, 4-acyl-reactions... 

Isoxazolin-5-one, 2,3-dimethyl-4-substituted photolysis, 6, 14 Isoxazolinones synthesis, 5, 132 Isoxazolin-3-ones alkylation, 6, 43 synthesis, 6, 106, 129 Isoxazolin-4-ones synthesis, 6, 106-107 Isoxazolin-5-ones alkylation, 6, 39 4,4-dialkyl substituted... 

The base-catalysed reaction of a-bromo-a,P-unsaturated ketones with aliphatic nitro compounds leads to 2-isoxazoline A-oxides by tandem conjugate addition-ring closure (Scheme 5) <95JOC6624>. A -Acyl-3-isoxazolin-5-ones are transformed into oxazoles by photolysis or by flash vacuum pyrolysis (Scheme 6) <96TL675>. 

Photolysis of the bicyclic isoxazoline 31 is believed to involve the intermediacy of the (Z)-azirine 33 (R1 = R2 = R3 = R4 = H), which subsequently ring-opens to the corresponding nitrile ylide 34.1,7-Electrocycliza-tion of the nitrile ylide 34 onto the enone system then leads to the 1,3-oxazepine 35 (Scheme 13) [73TL1835 74JCS(CC)373], Thermolysis of the closely related (Z)-azirines 33 (R1 = R3 = R4 = Ph), generated... 

Isoxazolin-5-one, 2,3-dimethyl-4-substituted photolysis, 6, 14 Isoxazolinones synthesis, 5, 132 Isoxazolin-3-ones alkylation, 6, 43 synthesis, 6, 106, 129 Isoxazolin-4-ones synthesis, 6, 106-107 Isoxazolin-5-ones alkylation, 6, 39 4,4-dialkyl substituted reaction with Grignard reagents, 6, 40 reactions with bases, 6, 41 synthesis, 6, 103-105 Isoxazolium bisulphate, 2,3,5-trimethyl-hydrogen exchange, 6, 21 Isoxazolium salts deprotonation, 5, 71 as hardeners for gelatin, 1, 363 nucleophilic cleavage, 6, 31 nucleophilic reactions, 6, 28-29 4/f-pyran synthesis from, 3, 761 reactions... 

Photolysis of the nitrite ester (49a), which was derived from isojervine, gave the isoxazolines (51a) and (52a) in a ratio of 3 1. The structures of these products were determined by spectroscopic studies, and were confirmed, in the case of isoxazoline (51a), by X-ray diffraction studies on the derived iodomethyl compound (51c).55 The 5,6-dihydro-derivative (49b) similarly gave isoxazolines (51b) and (52b) on irradiation.56 In each case, the isoxazolines isolated appear to be secondary products which are formed by cyclization of the initially formed unstable formyloxime derivatives (50) during chromatography on silica gel.55 56... 

As mentioned earlier, not much work has been done on 3-isoxazolines. Quaternization of the nitrogen atom in 3-isoxazoline is accomplished with methyl iodide <83LA906>. Photolysis of isox-azolinone (185) in the presence of diethylamine, resulted in E) and (Z) isomers of (187) via (186) along with diamide (1 ) via (188) (Scheme 28). The proposed mechanism is discussed <93AJC477>. The reaction between 3-methyl-3-isoxazolin-5-one (190) and benzoyl chloride afforded a mixture of iV-(191) and 0-benzoyl derivatives (192) (Scheme 29) <86CPB3153>. 

The photochemical behavior of the isoxazolidine ring is not extensively studied. Depending upon the experimental conditions, 5-nitroxazolidines undergo photolysis to yield either 4-isoxazolines by the elimination of nitrones or to P lactam derivatives, by ring opening followed by reclosure... 

A number of other approaches to 4-oxazolin-2-ones have been described, including hydrolysis of 2-amino-4,5-diphenyl-5-cyano-oxazole,150 photolysis of 3-hydroxyisoxazoles,151 and thermal rearrangement of an isoxazolin-3-one152 [Eq. (37)]. 

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