- Studies on asymmetric total synthesis of (?)-β-hydrastineviaa chiral epoxide ring-opening cascade cyclization strategy
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Herein, facile and enantioselective approaches to synthesize the core phthalide tetrahydroisoquinoline scaffold of (?)-β-hydrastineviaboth a CF3COOH-catalyzed (86% ee) and KHMDS-catalyzed (78% ee) epoxide ring-opening/transesterification cascade cyclization from chiral epoxide under very mild conditions are described. The key elements include a highly enantioselective epoxidation using the Shi ketone catalyst and an intramolecular CF3COOH-catalyzed cascade cyclization in one pot, and a late-stage C-3′ epimerization under MeOK/MeOH conditions as the key steps to achieve the first total synthesis of (?)-β-hydrastine (up to 81% ee).
- Cheng, Maosheng,Li, Jihui,Liu, Yongxiang,Meng, Jiaxin,Qin, Qiaohua,Song, Xinjing,Wu, Tianxiao,Zhao, Dongmei,Zheng, Yang
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p. 18953 - 18958
(2020/06/08)
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- Novel Zinc-Promoted Alkylation of Iminium Salts. New Synthesis of Benzylisoquinoline, Phthalidylisoquinoline, and Protoberberine Alkaloids and Related Compounds
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Zinc-promoted reductive coupling reaction of iminium salts with alkyl halides was found to be a successful key reaction for synthesis of a variety of alkaloids such as benzylisoquinoline, phthalidylisoquinoline, and protoberberine alkaloids.More specifically, laudanosine, cordrastine, hydrastine, narcotine, tetrahydropalmatine, and canadine were obtained.A new route for the synthesis of the emetine and yohimbine skeletons was exploited.
- Shono, Tatsuya,Hamaguchi, Hiroshi,Sasaki, Manji,Fujita, Shumei,Nagami, Kimihiko
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p. 1621 - 1628
(2007/10/02)
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- Some Reactions of β-Hydrastine
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β-Hydrastine (I) is an erythro compound, the chiral centres at C-1 and C-9 having R and S configurations respectively.Its conversion into the hitherto unknown threo-isomer by the reduction of the corresponding immonium derivative (II) with zinc and acetic acid has met with failure.Surprisingly, II with Zn/ AcOH regenerates β-hydrastine.During this reduction II rather suffers reductive cleavage yielding the non-nitrogenous lactone, meconine (IV).Sodium borohydride and catalytic reductions of II also fail to afford the threo-isomer.The latter is found to be extremely unstable as revealed from Dreiding model because of the severe steric interaction between the axial hydrogen at C-4 and the C1'-C2'bond.Benzylic oxidation of β-hydrastine (I) with MnO2, instead of producing the desired 4-oxo derivative (VI), gives 6,7-methylenedioxyisoquinoline arising out of cleavage at C1-C9 bond.
- Chatterjee, A.,Bhattacharyya, S.,Bhattacharyya, S.
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- NEW ELECTROREDUCTIVE SYNTHESIS OF PHTHALIDE ALKALOIDS
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Electroreduction of 2-methyl-3,4-dihydro-6,7-dimethoxy-isoquinolinium salt in the presence of 3-bromomeconine afforded Cordrastine.The method of cross coupling of immonium salts with bromophthalides was also applicable to other phthalide alkaloids.
- Shono, Tatsuya,Usui, Yoshihiro,Hamaguchi, Hiroshi
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p. 1351 - 1354
(2007/10/02)
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