- The palladium-catalyzed preparation of condensed tetracyclic heterocycles and their application to the synthesis of rac-mangochinine
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Dihydroisoquinoline derivatives and their analogues, prepared by the Bischler-Napieralsky reaction, were converted to their indole-fused derivatives. Scope and limitations of the palladium-catalyzed reaction, proceeding through the tautomeric enamine forms of these compounds, were studied and the process was extended to the preparation of racemic mangochinine. Georg Thieme Verlag Stuttgart.
- Vincze, Zoltan,Biro, A. Beatrix,Csekei, Marton,Timari, Geza,Kotschy, Andras
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p. 1375 - 1385
(2007/10/03)
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- Method for preparing certain acetonitriles
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This invention relates to a process for making certain acetonitriles.
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- Photochemical synthesis of 7,8-dioxygenated isoquinoline alkaloids
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A new approach to the synthesis of 7,8-dioxygenated tetrahydroisoquinoline alkaloids based on the photo-Fries rearrangement of esters derived from 3-hydroxy-4-methoxy phenylacetonitrile is reported. The procedure was applied to the synthesis of the alkaloid Arizonine and 1-benzyl tetrahydroisoquinoline precursor of cularine and 1,2-berbine alkaloids.
- Suau, Rafael,Valpuesta, Maria,Torres, Gregorio
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p. 1315 - 1318
(2007/10/02)
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- Biosynthesis of the A/B/C/D-Ring System of the Rotenoid Amorphigenin by Amorpha fruticosa Seedlings
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With phenylalanine as the starting point, the biosynthesis of the characteristic rotenoid A/B/C/D-ring system of amorphigenin is studied using Amorpha fruticosa seedlings.The course of the biosynthesis can be divided into four phases represented by the bordered and interconnecting Schemes 1, 3, 6 and 7 which summarise the Chalcone-Flavanone Phase, the Flavanone-Isoflavone Phase, the Hydroxylation/Methoxylation Phase and the Rotenoid Phase.By using an INADEQUATE NMR experiment involving the administration of acetate, the type of folding forming ring-D isdemonstrated by 13C-13C coupling and is interpreted as involving a polyketide containing a glutaconate segment which cyclises by a Claisen condensation.The resulting chalcone is cyclised, enzymically and stereospecifically, to 4',7-dihydroxyflavanone.The latter flavanone undergoes aryl migration, in a manner similar to that found in isoflavone biosynthesis, to give 7-hydroxy-4'-methoxyisoflavone.Possible mechanisms for the flavanone-isoflavone rearrangement are discussed, including a proposal that the initiating step involves attack on ring-A and is similar to the first stage of the aromatic hydroxylation of tyrosine to dopa.Although possessing no 4'-hydroxy group in ring-A, the mechanism is also applicable to the recently discovered rotenoids of the Boerhaavia and Iris type, and it provides an explanation for the biogenesis of natural spirobenzocyclobutanes from dihydroeucominoids.Six suitably substituted isoflavonoids labelled with 13C or 3H are synthesized and are used to show that the next hydroxylation (and probably methylation) involves C-3' rather than C-2' in 7-hydroxy-4'-methoxyisoflavone.Whilst the methylations involveS-adenosylmethionine, the hydroxylating enzymes are probably very similar to the flavanone-isoflavone-rearranging enzyme.The closure of ring-B to form finally the rotenoid system probably involves conjugate addition of a methoxyl radical.Prenylation and oxidative modifications are characteristically late-stage processes.
- Bhandari, Prabha,Crombie, Leslie,Daniels, Peter,Holden, Ian,Bruggen, Nicholas Van,Whiting, Donald A.
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p. 839 - 850
(2007/10/02)
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- Oxidation of Methoxy- and/or Methyl-Substituted Benzenes and Naphthalenes to Quinones and Phenols by H2O2 in HCOOH
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The oxidation of a number of arenes (methoxybenzenes, methylbenzenes, and naphthalenes) to quinones and phenols by H2O2 in HCOOH has been examined.Methoxybenzenes were much more easily oxidized to p-benzoquinones than methylbenzenes (e.g., 1,3,5-trimethoxybenzene was oxidized to 2,6-dimethoxy-p-benzoquinone in a 75percent yield and 1,2,4-trimethylbenzene to 2,3,5-trimethyl-p-benzoquinone in a 16percent yield).Electron-withdrawing substituents, such as nitro, cyano, and chloro groups, lowered the conversion of reactants and changed the product selectivity from quinones to phenols.Methoxybenzonitriles were oxidized to corresponding phenols in a moder ate yield (e.g., 2,6-dimethoxybenzonitrile to 3-hydroxy-2,6-dimethoxybenzonitrile in a 39percent yield and a 64percent selectivity).
- Orita, Hideo,Shimizu, Masao,Hayakawa, Takashi,Takehira, Katsuomi
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p. 1652 - 1657
(2007/10/02)
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