- Asymmetric syntheses of (?)-hastanecine, (?)-turneforcidine and (?)-platynecine
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Concise total asymmetric syntheses of three diastereoisomeric 1-hydroxymethyl-7-hydroxy substituted pyrrolizidines, (?)-hastanecine, (?)-turneforcidine and (?)-platynecine, are reported. The doubly diastereoselective conjugate additions of lithium (R)- or (S)-N-benzyl-N-(α-methylbenzyl)amide to tert-butyl (R,E)-4-(triethylsilyloxy)hepta-2,6-dienoate [which was prepared (in 96:4 e.r.) via Lewis acid mediated catalytic asymmetric allylation of tert-butyl (E)-4-oxobut-2-enoate] proceeded in both cases under the dominant control of the lithium amide reagent. Subsequent diastereoselective enolate allylations installed the required stereogenic centres, and the pyrrolizidine ring system was rapidly accessed by a two-step protocol (viz. ozonolysis and one-pot hydrogenolysis/double reductive cyclisation), to complete the asymmetric syntheses of (?)-hastanecine, (?)-turneforcidine and (?)-platynecine in 17, 8 and 24% overall yield, respectively, in eleven steps from commercially available 2,2-dimethoxyacetaldehyde in each case.
- Brambilla, Marta,Davies, Stephen G.,Fletcher, Ai M.,Roberts, Paul M.,Thomson, James E.
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p. 4523 - 4535
(2016/07/07)
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- An Efficient Synthesis of Racemic Necine Bases from a Common Intermediate
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Necine bases of pyrrolizidine alkaloids, turneforcidine, hastanecine, and platynecine are synthesized from ethyl 1-hydroxy-2,3,5,6-tetrahydro-1H-pyrrolizine-7-carboxylate in racemic form.
- Niwa, Haruki,Kuroda, Akio,Sakata, Tomoyo,Yamada, Kiyoyuki
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p. 2541 - 2543
(2007/10/03)
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- The tandem cycloaddition chemistry of nitroalkenes. A novel synthesis of (-)-hastanecine
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A short and efficient asymmetric synthesis of the pyrrolizidine necine base (-)-hastanecine is described. The key reaction in the synthesis is a sequential inter [4 + 2]/inter [3 + 2] cycloaddition. The Lewis acid promoted [4 + 2] cycloaddition between 2-
- Denmark,Thorarensen
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p. 5672 - 5680
(2007/10/02)
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- Practical asymmetric synthesis of hastanecine and dihydroxyheliotridane by a Claisen rearrangement/amine-epoxide-opening sequence
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A practical 13-step synthesis of the title compounds suitable for the gram scale has been developed. Key steps are Sharpless resolution, Claisen rearrangement, epoxidation and intramolecular S(N)2 ring closure to form the pyrrolizidine system.
- Mulzer,Scharp
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p. 615 - 622
(2007/10/02)
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- N-Acyliminium Ion Rearrangements: Generalities and Application to the Synthesis of Pyrrolizidine Alkaloids
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N-Acyliminium ions of the 2-aza-1,5-hexadienyl type frequently rearrange to isomeric ions by a process which is formally a 2-aza-Cope rearrangement.When gem-dimethyl substitution is present at C-4 of the initially formed N-acyliminium ion, the rearranged
- Hart, David J.,Yang, Teng-Kuei
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p. 235 - 242
(2007/10/02)
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