Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Photolysis 5,6-dihydro

Intramolecular attack of the carbenes shown in Scheme 30a provides benzo[6]cyclo-hepta[(5 ]-furans and -thiophenes, but the nitrogen analogue (X = NH) yields 9,10-dihydro-acridine 81AJC1037). Photolysis of 2-biphenyl isocyanide (Scheme 30b) (72JOC3571) and thermolysis of 2-biphenylsulfonyl diazomethane (Scheme 30c) (72CC893) also result in ring expansion. [Pg.106]

H- Pyran, rrans-2-methoxy-4-methyl-3,4-dihydro-conformation, 3, 630 2H-Pyran, 4-methyl-5,6-dihydro-photolysis, 3, 719 2H-Pyran, 6-methyl-3,4-dihydro- C NMR, 3, 586... [Pg.763]

Dihydro-9,10-epoxyphenanthrene and related arene oxides are of considerable interest as carcinogens formed by polycyclic aromatic hydrocarbons in vivo.45 Phenanthrene oxide does not isomerize to the corresponding dibenzoxepin under thermal conditions. Photolysis of... [Pg.10]

N. A-Diethyl-2.3-dihydro-8//-thieno[2,3-r/]azcpin-7-amine (20), which is obtained in 49 % yield by photolysis of 6-azido-2,3-dihydrothiophene in a mixture of diethylamine and tetrahydro-furan. on treatment with bromine yields the fully unsaturated derivative 21.1,4... [Pg.231]

With respect to using methyl viologen as electron relay, it might be of interest to note tlmt MV " can be oxidized by positive holes produced in illuminated colloidal semiconductors such as Ti02 Two oxidation products of MV are 1, 2 -di-hydro-l,r-dimethyl-2 -oxo-4,4 -bipyridylium chloride and 3,4-dihydro-l,r-dime-thyl-3-oxo-4,4 -bipyridylium chloride, which can readily be detected by their strong fluorescences at 516 nm and 528 nm, respectively. These products are also produced in the direct photolysis of MV " solutions and in the reaction of MV "" with OH radicals in homogeneous solution... [Pg.158]

Thiamin (vitamin B-l, 177) when photolysed, gives preparations having a characteristic odour. Photolysis of an aqueous solution with a high-pressure mercury lamp is reported to give the pyrimidine (178) [ 113]. Other work used irradiation at 254 nm and concentrated on the approximately 0.1% yield of ether-soluble odoriferous products. As many as nine compounds have been identified (179), (180), (181), 2-methyl-3-formyl-4,5-dihydrofuran, 3-acetyl-4,5-dihydrofuran, 4-oxopentyl formate, 3-formyl-5-hydroxypentan-2-one, 3-mercapto-2-methyl-4,5-dihydrofuran and bis(4,5-dihydro-2-methylfuran-3-yl)disulphide [114, 115]. [Pg.82]

Flash photolysis of 5-diazo-lO, ll-dihydro-dibenzo[a, d]cycloheptene (75) — which can be regarded as a bridged diphenyl-carbene — at room temperature in hquid paraffin first produced the spectrum of the triplet carbene 16, which then disappeared to give the electronic spectrum of the radical 17. The latter finally gave the dimer 5,5 -bi (10, ll-dihydrodibenzo[a, djcycloheptenyl) 18 2). [Pg.109]

Products isolated from the thermal fragmentation of A-arylbenzamide oximes and A-arylbenzamide O-phenylsulfonyl oximes have been accounted for by invoking a free-radical mechanism which is initiated by the preferential homolysis of the N-O bond." Time-resolved IR spectroscopy has revealed that photolysis of A, A -diphenyl-l,5-dihydroxy-9,10-anthraquinone diimine affords acridine-condensed aromatic products via excited-state intramolecular proton transfer." The absolute and relative rates of thermal rearrangements of substituted benzyl isocyanides have been measured,and it has been found that the relative rates are independent of temperature and exhibit excellent Hammett correlations. Thionitrosoarene (25), thought to be generated by desulfurization of the stable A-thiosulfinylaniline (24), has been established" " as an intermediate in the formation of 3,3a-dihydro-2,l-benzisothiazole (26) from o-alkylthionitrosoarene (24). [Pg.498]

Major photoproducts reported in soil treated with alachlor were 2, 6 -diethylacetanilide, 1-chloro-2, 6 -diethylacetanilide, 2,6-diethylaniline, chloroacetic acid, 2, 6 -diethyl-A -methoxy-methylaniline, and l-chloroacetyl-2,3-dihydro-7-ethylindole. Organic matter in soil enhanced the rate of photolysis (Chesters et al, 1989). [Pg.1544]

Photolysis of 2,1,3-benzothiadiazole-l-oxide produces l,3-dihydro-2,l,3-benzothiadiazole-2,2-dioxide, shown by flash photolysis to be formed via hydration of the 2-oxide intermediate... [Pg.364]

Similar structures appear to be intermediates in the photolysis of dihydro-pyrazines (Scheme 16), - and are also formed from the base treatment of certain iV-methyl-2i/-imidazolium salts (Section IV,D,2). ... [Pg.394]

Thermolysis or photolysis of l,3-diazabicyclo[3.1.0]hex-3-enes, as in Scheme 22, gives Al-ylides that have been trapped by a number of dipolar-ophiles. Thermolysis of 151 in diethyl acetylenedicarboxylate (DEAD) yielded 152 (R = Et) directly (Scheme 38), presumably via a dihydro intermediate. Using DMAD, a mixture of 152 (R = Me) and 153 was formed... [Pg.407]

Photolysis of the four examples of 2,3-dihydro-6f/-l,3-thiazines 101-104 resulted in the formation of different products which is dependent on R and R (Scheme 3). When both groups are methyl (101), isomeric thiazolines 105 and 106 are isolated, the thiazoline 106 being the major isomer. The ethyl analogue 102 reacts differently and the thioamide 107 is formed. All four thioamide isomers are formed when the benzyl analogue 103 is photolyzed and the... [Pg.579]

An interesting preparation of aliphatic diazoalkanes (R R C = N2 R, R = alkyl) involves the photolysis of 2-alkoxy-2,5-dihydro-1,3.4-oxadiazoles (see Scheme 8.49). When the photolysis is carried out in the presence of an appropriate dipolarophUe, the diazo compounds can be intercepted (prior to their further photolysis) by a [3 + 2] cycloaddition reaction (54). As an example, 2-diazopropane was intercepted with A-phenylmaleimide (54) and norbornenes (55) to give the corresponding A -pyrazolines. [Pg.547]

Photolysis at 280 nm of DMFU in methanol gave a product of composition DMFU CH3OH, which was decomposed by heating with IN HC1 to DMFU and is probably l,3-dimethyl-5-fluoro-5,6-dihydro-6-methoxyuracil, the analog to the hydrate. At shorter wavelengths... [Pg.223]

Only the head-to-tail adducts were obtained in the [2+2] photoaddition of 4-hydroxy-l-phenyl[l,8]naphthyridin-2(l//)-one with various alkenes in methanol (Scheme 3). The photolysis of the hypoiodites generated by the in situ reaction of the cycloadducts with excess mercury(ll) oxide-iodine reagent in benzene induced a regioselective scission of the non-ring junction bond of the alkoxyl radical to give substituted 3,9-dihydro-9-phenylyfuro[2,3- ][l,8]naphthyridin-4(2//)-one and/or 3,5-dihydro-5-phenylfuro[3,2-f][l,8]naphthyridin-4-(2//)-ones <1996T6125>. [Pg.716]

Valence tautomerization to the bicyclic azetine (47 R1 = OEt, R2 = Me) has been observed in the photosensitized (PlfcCO or PhCOMe) ring contraction of the otherwise photostable 2-ethoxy-4,5-dihydro-3.H-azepine (46 R4 = OEt, R2 = Me) (71JOC1934). In contrast, sensitized photolysis of the dimethylamino derivative (46 R1 = NMe2, R2 = H) gave only polymers. Unsensitized photolysis in pyrex yields several cyclic products, all of which are attributable to the intermediacy of an unstable 7-azabicyclo[3.2.0]hepta-3,6-diene (47 R1 = NMe2, R2 = H) (73CC327). [Pg.505]

Photorearrangement of the dihydro-2-methoxyazepine (48) in heptane is complex, yielding 19 products all in <5% yield In contrast, irradiation in benzene in the presence of a sensitizer (PhCOMe) yields, as sole product, not the expected bicyclic valence tautomer, but a photodimer of (48) via a symmetry allowed [ 2S+ 2S+0-2 ] ene reaction (73JOC1090). Sensitized photolysis in methanol affords the 3,4-methanol adduct. [Pg.505]


See other pages where Photolysis 5,6-dihydro is mentioned: [Pg.279]    [Pg.127]    [Pg.180]    [Pg.563]    [Pg.627]    [Pg.630]    [Pg.763]    [Pg.763]    [Pg.781]    [Pg.882]    [Pg.882]    [Pg.907]    [Pg.399]    [Pg.513]    [Pg.234]    [Pg.186]    [Pg.254]    [Pg.60]    [Pg.666]    [Pg.757]    [Pg.64]    [Pg.259]    [Pg.290]    [Pg.935]    [Pg.580]    [Pg.717]    [Pg.507]    [Pg.508]    [Pg.127]    [Pg.180]    [Pg.290]    [Pg.935]   
See also in sourсe #XX -- [ Pg.23 , Pg.102 ]




SEARCH



© 2024 chempedia.info