- Synthesis of phthalideisoquinoline and protoberberine alkaloids and indolo[2,1-α]isoquinolines in a divergent route involving palladium(0)- catalyzed carbonylation
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6,7,3',4'-Alkoxy-substituted 1-(2'-bromobenzoyl)-3,4-dihydroisoquinoline methiodides 17 were treated with sodium borohydride in methanol or acetic acid to give erythro-1-(2'-bromo-α-hydroxybenzyl)-2-methyl-1,2,3,4- tetrahydroisoquinolines 19. Treatment of 17 with lithium aluminum hydride in tetrahydrofuran gave the threo-isomer 20 in preference to the erythro 19. On the basis of studies on palladium(0)-catalyzed carbonylation of 2-bromo-3,4- dimethoxybenzyl alcohol to 6,7-dimethoxyphthalide, amino alcohol 19 or 20 was treated with a catalytic amount of palladium(II) acetate and triphenylphosphine in an atmosphere of carbon monoxide in the presence of chlorotrimethylsilane and potassium carbonate in boiling toluene to give the corresponding erythro- or threo-types of phthalideisoquinoline alkaloids 1 or 2, respectively. One-pot cyclization of the erythro-amino alcohols 19 was achieved by heating in N,N-dimethylformamide containing potassium carbonate to give 2,3,8,9- or 2,3,9,10-alkoxy-substituted 5,6-dihydroindolo[2,1- α]isoquinolines 3, which have a unique tetracyclic skeleton characteristic of dibenzopyrrocoline alkaloids. Similarly, palladium-(0)-catalyzed carbonylation of 1-(2'-bromobenzyl)tetrahydroisoquinolines 21 in the presence of excess potassium carbonate was found to give 8-oxoberbines 22, which on reduction with lithium aluminum hydride can be converted to protoberberine alkaloids 4.
- Orito, Kazuhiko,Miyazawa, Mamoru,Kanbayashi, Ryo,Tokuda, Masao,Suginome, Hiroshi
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p. 6583 - 6596
(2007/10/03)
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- 1-magnesiotetrahydroisoquinolyloxazolines as chiral nucleophiles in stereoselective additions to aldehydes: Auxiliary optimization, asymmetric synthesis of (+)-corlumine, (+)-bicuculline, (+)-egenine, and (+)-corytensine, and preliminary 13C NMR studies of 1-lithio- and 1-magnesiotetrahydroisoquinolyloxazolines
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Transmetalation of 1-lithiotetrahydroisoquinolyloxazolines with magnesium halides affords Grignard reagents that add to aldehydes with up to 80% selectivity for one of the four possible diastereomeric products. An oxazoline chiral auxiliary derived from camphor provides an optimal blend of diastereoselectivity and isomer separability. Synthetic applications of the optimal auxiliary, patterned after a literature approach in the racemic series, comprise an improved (formal) synthesis of bicuculline, egenine, and corytensine, as well as an efficient synthesis of corlumine. Preliminary NMR studies show that both 1-lithio- and 1-magnesiotetrahydroisoquinolyloxazolines are dynamic mixtures in THF solution at low temperatures. The barrier to pyramidal inversion of the secondary Grignard reagent is in the 9.8-10.1 kcal/mol range, while an upper limit of about 8.2 kcal/mol can be assigned to the barrier to the organolithium inversion.
- Gawley, Robert E.,Zhang, Pingsheng
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p. 8103 - 8112
(2007/10/03)
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- Studies on Carboxylation of Alkoxy-Substituted Benzyl Alcohols via Direct Lithiation and Bromine-Lithium Exchange: Synthesis of Phthalides and Phthalideisoquinoline Alkaloids
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Conversion of alkoxy-substituted benzyl alcohols to the corresponding phthalides by carboxylation via ortho lithiation and bromine-lithium exchange was studied.The method was applied to the key step in the synthesis of phthalideisoquinoline alkaloids.
- Orito, Kazuhiko,Miyazawa, Mamoru,Suginome, Hiroshi
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p. 2489 - 2496
(2007/10/02)
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- A FACILE SYNTHESIS OF PHTHALIDEISOQUINOLINES BY DECARBOXYLATION OF PHTHALIDECARBOXYLATES IN THE PRESENCE OF IMINE METHIODIDES
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Decarboxylation of potassium phthalide-3-carboxylates in the presence of acyclic imine methiodides in DMSO leads mainly to 2-acylbenzamides, but with 3,4-dihydroisoquinolinium methiodides, a one step synthesis of phthalideisoquinolines is achieved in mode
- Chiefari, John,Janowski, Wit K.,Prager, Rolf H.
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p. 863 - 867
(2007/10/02)
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- Synthesis of phthalideisoquinolines from 3-halophthalides and 3,4-dihydroisoquinolinium salts
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Phthalideisoquinoline alkaloids have been synthesized by coupling appropriately substituted 3-halophthalides and 2-methyl-3,4-dihydroisoquinolinium salts in the presence of Zn(Cu) couple or metallic Zn.Both erythro and threo isomers are formed in the reaction.The nmr spectra of the (+/-)-erythro- and (+/-)-threo-isocordrastines have been reinvestigated.The results, which differ from those previously reported, lead to a different conclusion regarding the conformations of the molecules.
- Slemon, Clarke E.,Hellwig, Louise C.,Ruder, Jean-Pierre,Hoskins, Eric W.,MacLean, David B.
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p. 3055 - 3060
(2007/10/02)
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