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Photocyclization of stilbenes

Phosphoryl-stabilized anions, 25, 2 Photochemical cycloadditions, 44, 2 Photocyclization of stilbenes, 30, 1 Photooxygenation of olefins, 20, 2 Photosensitizers, 20, 2 Pictet-Spengler reaction, 6, 3 Pig liver esterase, 37, 1 Polonovski reaction, 39, 2... [Pg.592]

Polycyclic aromatic compounds, synthesis by photocyclization of stilbenes, 30, 1... [Pg.593]

The photocyclization of stilbene and its simple derivatives to phenanthrene and substituted phenanthrenes is now a well-documented and useful synthetic reaction the scope and mechanism of this reaction have been thoroughly reviewed by Stermitz.344 There... [Pg.87]

The photocyclization of stilbenes to phenanthrenes has been used in the synthesis of the aporphine ring system347,348 conversion of the... [Pg.88]

Oxidative photocyclization of stilbene to phenanthrene, which was discovered in 1960, was first applied to the synthesis of [7]helicene by Martin and coworkers in 1967 [26, 44, 45]. This approach was extended to the syntheses of long [njhelicenes (n < 14) and [n]thiahelicenes (n < 15), using both mono- and diannelations. Numerous [nfhelicenes (n < 13) and [n]thiahelicenes (n < 13) were obtained in non-racemic form via the following methods (1) seeded crystallization of conglomerate (e.g. [7]-, [8]- and [9]helicene) [46, 47], (2) resolution by chromatography (e.g. [13]thiahelicene) [48] and (3) photocyclization from a resolved precursor (e.g. [13]helicene from hexahelicene-2-carboxylic acid) [49]. The oxidative photocyclization of stilbenes is still the method of choice for the preparation of selected [n]helicenes and their heteroatom analogs [50-58]. [Pg.549]

Syntheses of [n]helicenes (and [n]thiahelicenes) via oxidative photocyclizations of stilbenes have serious constraints. They must be carried out in dilute solutions ( 1 mM) and the functional groups that significantly affect relaxation of the singlet excited states of stilbenes such as bromo, iodo, keto, amino and nitro, are typically not compatible for longer helicenes, problems with regioselectivity of photocyclization may be encountered [61]. These limitations have spurred the recent developments of nonphotochemical syntheses for efficient preparation of highly functionalized, nonracemic helicenes. [Pg.551]

The first double helicenes, consisting of head-to-tail annelated [6]helicenes, were prepared by oxidative photocyclization of stilbenes to helicenes [21]. Recently, double helicene 48, in which two benzene rings are shared by [5]- and [7]helicene, was prepared via nonphotochemical Pd-catalyzed cydotrimerization of 3,4-didehydrophenanthrene derived from 47 (Fig. 15.17) [88]. The H NMR spectrum for racemic 48 showed better agreement with the calculated spectrum for the diastereomer with homochiral versus heterochiral helicenes. The characterization of double helicenes did not indude X-ray crystallography [21, 88],... [Pg.560]

One process which is related to the photocyclization of stilbene-like substrates is the conversion of 2-vinyl biphenyls to 8,9a-dihydrophenanthrenes, which undergo a facile thermal isomerization to 9,10-dihydrophenanthrenes (Scheme 9.24) [36]. For the synthesis of 5,6-dihydro- 1,10-phenanthroline and 1,10-phenanthroline derivatives, metal-chelation of the nitrogen atoms has shown to be productive (Scheme 9.25) [37]. [Pg.299]

Photocyclization of arylimines. The photocyclization of stilbenes to phen-anthrenes (13, 231) can be extended to arylimines such as 1 when BF, etherate is used as activator for the imines. [Pg.47]

Phenanthrenequinone from benzoin. The photocyclization of stilbene to phenanthrene requires a trans to cis isomerization. This step can be circumvented by reaction of benzoin with phenylboric acid to form the 1,3-dioxoborole 2. This adduct can be converted to phenanthrenequinone by photocyclization in the presence of diphenyl diselenide as the oxidant. [Pg.254]

The photocyclization of stilbenes (211) (including its in situ oxidation) to phenanthrenes (213) and that of conjugated arylalkenes to polycyclic aromatics constitute one of the most studied and widely used applications of organic photochemistry. Its potential synthetic utility is amplified by the existence of a number of natural products (mainly alkaloids) that contain a phenanthrene subunit in their structure. In view of the plethora of examples contained in several excellent reviews, only selected examples will be presented here with focus on the selectivity of the process. [Pg.723]

Lewis and coworkers have studied the sensitized photocyclization of stilbene-linked primary amines 300 which gave 302, in good yields (Scheme 68) [293],... [Pg.1102]

The photochemistry of substituted furans can be very complex indeed and may differ considerably from that found for benzenoid compounds. However, the photocyclization of 2,2 -ethylenedifuran to a benzodifuran is a simple reaction that is an exact counterpart to the photocyclization of stilbene to phenanthrenes.19 Some side chains allow ready dissociation to radicals typical is the nitro group and Scheme 4 displays what happens to irradiated... [Pg.242]

The combination of oxygen and iodine is the most satisfactory system found for the photocyclization of stilbenes to phenanthrenes. " Thus a mixture of trans-stilbene (0.01 m.) and iodine (0.005 m.) in cyclohexane on irradiation with a mercury... [Pg.252]

Photocyclization of haloarenes into heterocycles 81CSR181. Photocyclization of stilbene analogues with formation of condensed... [Pg.285]

This is an important reaction which competes with cis - trans photoisomerization of stilbenes even at low concentrations in solution or in the gas phase [470]. First observed for cis-stilbenc by Smakula [94] and identified by Moore et al. [471], it has been intensively studied by Mallory [472], Laarhoven [473], and several other groups [82, 125, 474-483]. In general, photocyclization of stilbenes provides a valuable synthetic route for generation of phenanthrenes. [Pg.73]

Photocyclization of Stilbenes and Related Molecules Frank B. Mallory and Clelia W. Mallory... [Pg.424]

A good review of the 4a,4 >-dihydrophenanthrenes formed by photocyclization of stilbenes has appeared, which includes details of evidence for the stereochemistry at the ring junctions. A stilbene (125) substituted with a long-chain... [Pg.369]

Scheme 13.29 Photocyclization of stilbene derivatives towards heteroatom-containing PAHs 104-106. Scheme 13.29 Photocyclization of stilbene derivatives towards heteroatom-containing PAHs 104-106.
Experimental data on photocyclization of stilbenes and related indolic compounds such as bisphenylazostilbene were reported in Ref [5]. The stereoselectivity of the formation of macrocyclic stilbenes as well as the regioselectivity of their photocyclization are strongly influenced by the length of the connecting alkanediyl chain [6]. Photochemical cyclization reaction in cis-3,3, 5,5 -tetramethoxystilbene was investigated [7]. The reaction occurred to give dihydrophenanthrene-type... [Pg.137]

Diatropic effects of polycyclic compounds (162), which were synthesized by intramolecular photocyclization of stilbene derivatives (161), were investigated about a flanking phenyl ring on nearby CH and CF bonds (Scheme 31)7 ... [Pg.108]

Helicenes and helicene-like molecules possessing nonplanar ortho-fused scaffolds exhibit helical chirality. Enantiopure forms of these molecules are potentially applicable to optical or electronic functional materials and chiral reagents [1], Therefore, development of their practical enantioselective synthesis, which can introduce various substituents on their frameworks, is highly attractive. The classical nonasymmetric synthesis of helicenes is based on an oxidative photocyclization of stilbene-type precursors [2]. However, this method suffers from low product yields and low substrate concentrations. Thus, several nonphotochemical synthetic methods have been developed which have been applied to the synthesis of enantioenriched helicenes [3]. Among them, a [2 - - 2 - - 2] cycloaddition strategy is highly attractive because of its convenient operation and its applicability to the catalytic enantioselective synthesis. The synthesis of helicenes and helicene-like molecules by transition-metal-mediated [2 -I- 2 -I- 2] cycloaddition reactions, including enantioselective variants, is summarized in this section. [Pg.281]


See other pages where Photocyclization of stilbenes is mentioned: [Pg.276]    [Pg.2]    [Pg.255]    [Pg.699]    [Pg.334]    [Pg.276]    [Pg.156]    [Pg.699]    [Pg.511]    [Pg.193]    [Pg.529]    [Pg.407]    [Pg.408]    [Pg.45]    [Pg.47]    [Pg.107]    [Pg.676]    [Pg.695]   
See also in sourсe #XX -- [ Pg.30 ]




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Photocyclization of stilbene

Photocyclization of stilbene

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