The products formed on UV irradiation of several tricyclic compounds (i.e. 3 , 6 , 8 , 15 , and 17 , Schemes 2-4) were studied in detail. A marked dependence of the reaction course on the type and site of substitution was found. Among the several light-induced transformations, a novel rearrangement, i.e. 11 to 9 (Scheme 3) was identified. The formation of the polycyclic compound 13 on irradiation of 8a (Scheme 3) resulted from an unexpected skeletal rearrangement with dearomatization of one benzene ring. The structures of compounds 10 , 11 , and 13 were established by X-ray crystallography (Figs. 1-3). An attempt was made to give a general mechanistic picture of all observed photochemical results (Schemes 4-6). 相似文献
2-Substituted benzo[b]furans were synthesized by a one-step metal-free photochemical reaction between 2-chlorophenol derivatives and terminal alkynes by tandem formation of an aryl-C and a C-O bond via an aryl cation intermediate. The mild conditions and the application to chlorophenols rather of the more expensive bromo or iodo analogues makes this procedure environmentally convenient. 相似文献
Methylated polycyclic aromatic hydrocarbons (PAHs) are suspected to be some of the toxic compounds in crude oil towards marine life and are needed as single compounds for environmental studies. 1-, 3- and 6-methylchrysene (3a,b,c) were prepared as single isomers by photochemical cyclization of the corresponding stilbenoids in the Mallory reaction using stoichiometric amounts of iodine in 82-88% yield. 2-methylchrysene (3d) was prepared by photochemical cyclization where the regioselectivity was controlled by elimination of an ortho-methoxy group under acidic oxygen free conditions in 72% yield. These conditions failed to form 4-methylchrysene from the corresponding stilbenoid. All stilbenoids were made from a common naphthyl Wittig salt and suitably substituted benzaldehydes. We have also demonstrated that methylchrysenes can be oxidized to the corresponding chrysenecarboxylic acids by KMnO4 in modest yields. 相似文献
Irradiation of the dienone methyl ether 3a furnished the unstable regioisomeric photoadducts 4a and 5a which on Lewis acid-catalyzed fragmentation afforded the tricyclic diketones 6,7 and 8 . The same mixture was obtained from the isobutyl ether 3b (Scheme 2). 相似文献
2,2-Dipropionylazoxybenzenes undergo rearrangement to the corresponding 3-[1-alkoxy-1-(2-propionylarylamino)ethyl]benzo[c]isoxazoles in the case of base catalysis; this transformation is realized only in the case of ortho,ortho' orientation of the propionyl groups in the substrate molecule and with the participation of the solvent as a reagent. A mechanism for the rearrangement that assumed the participation of one of the propionyl groups in intramolecular reduction of the azoxy group to an azo group is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 743–748, June, 1983. 相似文献
Irradiation of 2-cyanochromone in the presence of olefins gave rise to [3 + 2] cycloadducts together with the formation of normal [2 + 2] cycloadducts with the product ratio being temperature-dependent. The mechanism involving a vinyl nitrene intermediate was proposed. 相似文献
The UV. irradiation of 17β-acetoxy-4α, 5α-epoxy-2-oxaandrostan-3-one ( 7 ) yields 17β-acetoxy-2-oxa-10(5 → 4)abeo-4ζ (H)-androsta-3,5-dione ( 11 ). A non-photochemical synthesis of 11 , proceeding in lower yield, is also described. 相似文献
The intricate frameworks of paracyclophanes are an important target for synthesis since they are found in various chiral auxiliaries, solar cells, high-performance plastics, pharmaceuticals, and molecular machines. Whereas numerous methods exist for the preparation of symmetric paracyclophanes, protocols for the efficient synthesis of strained asymmetric scaffolds are limited. Here we report a remarkably simple photochemical route to strained [3.2]paracyclophanes starting from readily available educts. By way of NMR and X-ray analyses, we discovered that UV-irradiation of an aromatic carboxylic ester tethered to a toluene moiety leads to the intramolecular formation of a new C−C bond, with loss of an alcohol. A systematic evaluation of the reaction conditions and substituents, as well as radical starter and triplet quenching experiments, point to a reaction mechanism involving an excited triplet state and hydrogen atom transfer. The new method proved to be robust and versatile enabling the synthesis of a range of cyclophanes with different substitutions, including an unusual diastereoisomer with two planar chiral centers, and thus proved to be a valuable addition to the synthetic toolbox. 相似文献
Summary: Polymerization as a result of photocrosslinking is one of the most versatile technologies for producing organic polymers. This article highlights the formation of crosslinking in metal coordination polymers in the solid‐state using a photochemical approach and its importance in material science. Past and current developments of solid‐state photochemical [2+2] cycloaddition in organic and inorganic systems relevant to the topic are reviewed. The challenges for the coordination chemist in utilising this rational approach to orient the coordination polymers and the scope of this work are delineated.
The CC‐containing molecules can be aligned by metal coordination bonds in such a way as to promote crosslinking by a photochemical [2+2] cycloaddition reaction. 相似文献
A conrotatory photocyclization , a novel [1,9] hydrogen shift, and a lateral ring opening are involved in the rearrangement of a series of 2-(4-alkylstyryl)furans 1 to 5-(3-alkylbutadienyl)benzo[b]furans 2 in dichloromethane. These novel photochemical rearrangements occur with good yields of isolated products. 相似文献
Regioselective generation of the C(2)-carbocation a of tricyclo[4.2.2.01,5]decane ( 1 ) by treatment of both corresponding epimeric alcohols 5 and 6 with BF3 and trapping the rearranged tricyclo[5.3.0.04,8]decan-7-yl carbocation b with Et3SiH as hydride-ion donor (ionic hydrogenation) gives the corresponding hydrocarbon 3 as sole product in almost quantitative yield. The latter is a known intermediate in the Lewis-acid-catalyzed rearrangement of 1 to adamantane ( 4 ). 相似文献
An extremely short synthesis of 2,2-dimethyl-3-hydroxymethyl cyclopentanone 2 (R1 = R2 = Me), an advanced intermediate in the synthesis of the pheromone planococcyl acetate 3, is described. 相似文献
A new two step synthesis of benzo[b]quinolizine ring systems via the rearrangement of 2-[1(3H)-oxodihydrobenzo[c]furan-3-yl] quinuclidin-3-ones is described. 相似文献