- First synthesis of naturally occurring (±)-epi-conocarpan
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(±)-epi-Conocarpan 1 was synthesized via the key intermediate 5-bromo-cis-2-(4-methoxyphenyl)-3-methyl-2,3-dihydrobenzofuran 6 which was synthesized by a ruthenium(II) porphyrin-catalyzed intramolecular C-H insertion reaction using aryl tosylhydrazone salt 5 as the carbene source, starting from the commercially available 5-bromo-2-hydroxyacetophenone.
- Zheng, Shi-Long,Yu, Wing-Yiu,Xu, Ming-Xia,Che, Chi-Ming
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- Enantioselective Oxy-Heck–Matsuda Arylations: Expeditious Synthesis of Dihydrobenzofuran Systems and Total Synthesis of the Neolignan (?)-Conocarpan
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This work discloses the first examples of an effective enantioselective oxy-Heck–Matsuda reaction using a variety of styrenic olefins to generate chiral dihydrobenzofurans. The reaction proceeds in moderate to good yields, with high trans diastereoselectivity (up to 20:1) in enantioselectivities up to 90:10 using the N,N-ligand pyrimidine-bisoxazoline (PyriBox). The oxy-Heck–Matsuda reactions were carried out under mild conditions and rather low catalyst loadings. The feasibility and practicality of the process is demonstrated by a concise total synthesis of the neolignan (?)-conocarpan. X-ray diffraction of an advanced brominated intermediate in the route to (?)-conocarpan has allowed the unequivocal assignment of the absolute stereochemistry of the oxy-Heck–Matsuda aryldihydrobenzofuran products. A rationale for the mechanism operating in these enantioselective oxy-Heck–Matsuda reactions is also presented. (Figure presented.).
- Silva, Allan R.,Polo, Ellen C.,Martins, Nelson C.,Correia, Carlos Roque D.
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p. 346 - 365
(2018/01/26)
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- Concise asymmetric synthesis of (+)-conocarpan and obtusafuran
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The asymmetric synthesis of three natural products: (+)-conocarpan, both (+)- and (-)- obtusafuran is disclosed. The highlights of the synthesis are the enantioselective hydrogenation of prochiral ketones via dynamic kinetic resolution to afford chiral alcohols. Intramolecular ring closure via either Sr reaction or metal-catalyzed C-O bond formation led to the construction of the trans-dihydrobenzofuran core. Georg Thieme Verlag Stuttgart · New York.
- Chen, Cheng-Yi,Weisel, Mark
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p. 189 - 192
(2013/02/26)
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- Cerium ammonium nitrate-mediated the oxidative dimerization of p-alkenylphenols: A new synthesis of substituted (±)-trans- dihydrobenzofurans
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A new method for the preparation of substituted dihydrobenzofurans is described. The p-alkenylphenols, mediated by cerium ammonium nitrate (CAN), undergo the oxidative dimerization to generate substituted dihydrobenzofurans including (±)-conocarpan, (±)-licarin A, (±)-acuminatin, as well as their related substituted dihydrobenzofurans.
- Chen, Po-Yuan,Wu, Yi-Hua,Hsu, Mon-Huei,Wang, Tzu-Pin,Wang, Eng-Chi
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p. 653 - 657
(2013/07/27)
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- Asymmetric synthesis of neolignans (-)-epi-Conocarpan and (+)-Conocarpan via Rh(II)-catalyzed C-H insertion process and revision of the absolute configuration of (-)-epi-Conocarpan
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(Chemical Equation Presented) Catalytic asymmetric synthesis of neolignan natural products (-)-epi-conocarpan and (+)-conocarpan has been achieved by exploiting an enantio- and diastereoselective intramolecular C-H insertion reaction to construct a cis-2-
- Natori, Yoshihiro,Tsutsui, Hideyuki,Sato, Naoki,Nakamura, Seiichi,Nambu, Hisanori,Shiro, Motoo,Hashimoto, Shunichi
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supporting information; experimental part
p. 4418 - 4421
(2009/09/06)
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- Synthesis of (-)-conocarpan by two routes based on radical cyclization and establishment of its absolute configuration
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Two independent routes for the total synthesis of the bioactive neolignan (-)-conocarpan are described. The first (98% ee) is based on formal radical cyclization onto a benzene ring, and involves a 5-exo-trigonal closure onto a double bond restrained within a 6-membered ring. The second route (88% ee), which is shorter, is based on 5-exo-trigonal cyclization of an aryl radical onto a pendant terminal double bond. The two routes differ in their degree of stereoselectivity. The absolute configuration originally assigned to (+)-conocarpan had previously been called into question on the basis of empirical chiroptical rules; the present chemical work confirms the need for revision, and the assigned absolute configurations of several compounds correlated with (+)-conocarpan must also be changed. The Royal Society of Chemistry.
- Clive, Derrick L. J.,Stoffman, Elia J. L.
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experimental part
p. 1831 - 1842
(2008/10/09)
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- Total synthesis of (-)-conocarpan and assignment of the absolute configuration by chemical methods
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(-)-Conocarpan (1) was synthesized by a method based on radical cyclization, and the absolute configuration was established by chemical degradation; the original 2R,3R-assignment to (+)-conocarpan should be reversed, as suggested by a later chiroptical study of model 2,3-dihydrobenzofurans. The Royal Society of Chemistry.
- Clive, Derrick L. J.,Stoffman, Elia J. L.
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p. 2151 - 2153
(2008/02/08)
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- Synthesis of 2,3-dihydrobenzofurans by Mn(OAc)3-based oxidative cycloaddition of 2-cyclohexenones with alkenes. Synthesis of (±)-conocarpan
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Oxidative cycloaddition of a 2-cyclohexenone or α-tetralone and an alkene with dried Mn(OAc)3 in benzene at 80-140 °C provides a general route to dihydrobenzofurans 15 and dihydronaphthofurans 17. Although the yields are modest, this one-pot reaction provides simple access to these compounds, which have previously been prepared by multistep routes. Oxidative cycloaddition of 2-cyclohexenones with β-methylstyrenes provides a new route to benzofuranoid neolignans, which was applied to the synthesis of conocarpan (22). The formation of 2-acetoxyhexanedioic acids 27 and 47 from acetoxylation of 2-cyclohexenones in HOAc, but not in benzene, opens up a new class of Mn(OAc)3 reactions and explains Watt and Demir's discovery that much higher yields of α'-acetoxy enones are obtained in benzene than in HOAc.
- Snider, Barry B.,Han, Luning,Xie, Chaoyu
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p. 6978 - 6984
(2007/10/03)
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