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1.
The synthesis of 2-(1H-imidazol-1-yl)-2,3-dihydro-2H-1-benzopyran-4-ones (I) through 3-bromo-2,3-dihydro-4H-1-benzopyran-4-ones or more conveniently through chroman ring closure from 2-(1H-imidazol-1-yl)-2′-hydroxyacetophenones is described. The ring closure also works well for the pyrazolyl derivatives. Compounds I and the corresponding imidazolylchromanols, -chromenes, and -chromans derived from the former, were pharmacologically investigated. 相似文献
2.
The synthesis of 2-methyl-3-(1-methyl-1H-imidazol-2-yl)-4H-1-benzopyran-4-ones 4 is described starting from 2-acetoxybenzoyl chlorides and 1,2-dimethylimidazole. Chromones 4 undergo alkaline ring opening to the corresponding 1-(2-hydroxyphenyl)-2-(1-methyl-1H-imidazol-2-yl)ethenols 5 which give ring closure to 2-substituted 3-(1-methyl-1H-imidazol-2-yl)-4H-1-benzopyran-4-ones or 2,3-dihydro-3-(1-methyl-1H-imidazol-2-yl)-4H-1-benzopyran-4-ones. The corresponding chromanols and chromenes can be easily obtained from chromones 4 . 相似文献
3.
The synthesis of 2-(1H-imidazol-1-yl)-4H-1-benzothiopyran- 4 -ones 3 from 3-bromo-4H-1-benzothiopyran-4-ones 1 and imidazole is described. The reaction of 1 with secondary amines gives the corresponding 3 -amino-thiochromones 11. Compounds 3 can be oxidized to the sulfones 4 from which the thiochromanols 5 and thiochromene 7 can be easily obtained. 3-Bromo-2,3-dihydro-6-methyl-4H-1-benzothiopyran-4-one 12 and imidazole led by dehydrohalogenation to thiochromone, while the ketal 13 rearranged to benzo[b]thiophene 16. 相似文献
4.
The diethyl ether extract of the Japanese liverwort Metacalypogeia cordifolia yielded five new chroman type derivatives in addition to known sesquiterpenoids. One of the new chroman derivatives was also isolated from the ether extract of another liverwort, Cephalozia otaruensis. Their structures were established by extensive two dimensional (2D) NMR techniques and chemical evidence. They were shown to be 2,2-dimethyl-7-(3-methyl-2-butenyl)-chroman derivatives. This was the first example of the isolation of the chroman-type compounds, although various types of aromatic compounds have been isolated from liverworts. 相似文献
5.
Hashmi AS Rudolph M Bats JW Frey W Rominger F Oeser T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(22):6672-6678
Different furans containing an ynamide or alkynyl ether moiety in the side chain were prepared. The gold-catalyzed transformation of these compounds delivered dihydroindole, dihydrobenzofuran, chroman, and tetrahydroquinoline derivatives at room temperature through very fast reactions. Furthermore, the stabilizing effect of the heteroatom directly attached to the intermediate arene oxides led to highly selective reactions, even in the case of only mono-substituted furans, which is quite different from previous results obtained with non-heteroatom-substituted alkynes. 相似文献
6.
Zhipeng Guan Xingxing Zhong Yayu Ye Xiangwei Li Hengjiang Cong Hong Yi Heng Zhang Zhiliang Huang Aiwen Lei 《Chemical science》2022,13(21):6316
Due to the importance of chroman frameworks in medicinal chemistry, the development of novel synthetic methods for these structures is gaining increasing interest of chemists. Reported here is a new (4 + 2) radical annulation approach for the construction of these functional six-membered frameworks via photocatalysis. Featuring mild reaction conditions, the protocol allows readily available N-hydroxyphthalimide esters and electron-deficient olefins to be converted into a wide range of valuable chromans in a highly selective manner. Moreover, the present strategy can be used in the late-stage functionalization of natural product derivatives and biologically active compounds, which demonstrated the potential application. This method is complementary to the traditional Diels–Alder [4 + 2] cycloaddition reaction of ortho-quinone methides and electron-rich dienophiles, since electron-deficient dienophiles were smoothly transformed into the desired chromans.We have developed a (4 + 2) radical annulation approach for the synthesis of diverse chromans. This method is complementary to the traditional Diels–Alder [4 + 2] annulation of ortho-quinone methides and electron-rich dienophiles.Chroman moieties frequently exist as the key subunit in a wide array of natural products, pharmaceuticals, and bioactive molecules.1 For example, vitamin E,2 centchroman,2 cromakalim3 and rubioncolin B4 are well-known active pharmaceutical ingredients in various therapeutic areas (Scheme 1a). Due to their significant importance in medicinal chemistry, developing new methods towards the synthesis of chromans and the installation of a variety of the functional groups in chroman frameworks are gaining increasing attention of the chemical community.5Open in a separate windowScheme 1Selected bioactive molecules and the synthetic methods of chromans.In the past few decades, a great deal of methods have been developed for the assembly of substituted chromans, and among them, the Diels–Alder [4 + 2] cycloaddition reaction provides a highly efficient synthetic platform in the construction of these functional six-membered frameworks.6 Extensive work has been done with this strategy, resulting in a lot of significant progress. The ortho-quinone methides (o-QMs) are generally essential dienes for the Diels–Alder reaction towards the synthesis of chromans, as they are highly reactive for rapid rearomatization via Michael addition of nucleophiles, cycloaddition with a dienophile of 2π partners or 6π-electrocyclization (Scheme 1b).7 Herein, although various valuable chromans have been successfully synthesized with the Diels–Alder [4 + 2] cycloaddition reaction, the use of o-QMs may lead to several potential limitations in some cases. One of the potential limitations is that o-QMs are used mainly as Michael acceptor and electron-deficient dienes to react only with nucleophiles and electron-rich dienophiles. In these considerations, the evolution of synthetic methods for chromans is very important and highly desirable. In particular, novel (4 + 2) cycloaddition strategies capable of synthesizing chromans with the use of easily available materials and electron-deficient dienophiles are of utmost interest.On the basis of retrosynthetic analysis of chroman shown in Scheme 1c, (4 + 2) radical annulation of the corresponding carbon-centered radical R with olefin would be an alternative route, which is able to overcome the above-mentioned potential limitations. Considering that radical species R is normally nucleophilic, thus, it could react with electron-deficient olefins affording chroman products that generally can''t be synthesized by the traditional Diels–Alder [4 + 2] cycloaddition reaction involving o-QMs. Herein, we reported a highly selective (4 + 2) radical–annulation reaction to construct the chroman framework with the use of easily available NHPI ester as the radical precursor and olefin as the radical acceptor under mild conditions.Compared with other alkyl radical precursors, the redox-active N-(acyloxy)phthalimides (NHPI esters) come to the fore, since they are cheap, stable, readily available, and non-toxic.8 Bearing above hypothesis in mind, we commenced to investigate the (4 + 2) annulation reaction by utilizing readily available N-hydroxyphthalimide ester A′ and commercially available ethyl acrylate as model substrates. After a great deal of screening on the reaction parameters, only a trace amount of the target product was detected by GC-MS. In contrast, the main product is anisole, which may result from a rapid hydrogen abstraction reaction of the unstable primary alkyl radical intermediate. To restrain the formation of this by-product, we designed N-hydroxyphthalimide esters A and A′′, which could produce more stable tertiary radicals, for the target (4 + 2) annulation reaction instead of A′ (9 74% yield of ethyl-2,2-dimethylchromane-4-carboxylate upon 1 was selectively obtained after irradiation of the reaction system under blue LEDs at room temperature for 12 h, despite a little by-product ( Entry Variation from standard conditions Yield/% 1 None 74 2 No light n.d 3 No EY n.d 4 4-CzIPN n.d 5 Ru(bpy)3(PF6)2 36 6 MeCN 34 7 DCE n.d 8 Air 39