- Ring expansion of azetidinium ylides: Rapid access to the pyrrolizidine alkaloids turneforcidine and platynecine
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(Chemical Equation Presented) Azetidinecarboxylate esters react readily with metallocarbenes in an inter- or intramolecular fashion to generate azetidinium ylides. Efficient [1,2]-shift by the ester-substituted carbon furnishes ring-expanded pyrrolidine p
- Vanecko, John A.,West
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- Synthesis of bridged azabicyclic compounds using radical translocation reactions of 1-(o-halogenobenzoyl)-2-(prop-2-enyl)-and -(prop-2-ynyl)-piperidines
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Methyl 1-(o-bromobenzoyl)-2-(prop-2-enyl)piperidine-2-carboxylate 8a, upon treatment with tributyltin hydride in the presence of azoisobutyronitrile in boiling toluene gave regioselectively the 8-azabicyclo[3.2.1]octane 14a (a 5-exo cyclisation product) in quantitative yield as a diastereomeric mixture (66:34). 1-(o-Bromobenzoyl)-2-(prop-2-enyl)piperidine 13 also gave the 8-azabicyclo-[3.2.1]octane 16 (75% as a diastereomeric mixture), along with the pyrido[2,1-a]isoindolone 17 (10%) and the simple reduction product 18 (5%). 1-(o-Iodobenzoyl)-2-[3-(trimethylsilyl)prop-2-ynyl]piperidine 23 afforded, in addition to the pyrido[2,1-a]isoindolone 25 (18%), the 8-azabicyclo-[3.2.1]octane 24 (75%) which was converted into the 6-oxo derivative 27. For comparison, the behaviour of the azetidine congener 31 was also examined.
- Ikeda, Masazumi,Kugo, Yasuhiro,Sato, Tatsunori
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p. 1819 - 1824
(2007/10/03)
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- 2-Amino Ketene S,S-Acetals as α-Amino Acid Homoenolate Equivalents. Synthesis of 3-Substituted Prolines and Molecular Structure of 2-(N-Pivaloylpyrrolidin-2-ylidene)-1,3-dithiane
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Allylic deprotonation of the heterocyclic 2-amino ketene S,S-acetal 8a, followed by regioselective γ-alkylation reaction of the resulting organolithium 10 (a proline homoenolate equivalent) with electrophiles, leads to adduct 11.Controlled hydrolytic cleavage of 11 gives a series of 3-substituted prolines, including the conformationally-constrained aspartate and glutamate derivatives, 14e and 14f respectively.The bicyclic thiolactam 18 has been prepared in an attempt to provide an asymmetric variant of organolithium 10 but efforts to generate the requisite ketene N,S-acetal 19 were unsuccessful.Extension of the ketene S,S-acetal chemistry to other ring sizes has been examined within the context of substituted azetidine-2-carboxylates.Condensation of the protected amino ester 20 with AlMe3-HS(CH2)3SH was complicated, however, by the reactivity of the four-membered ring and led to the ring-opened adduct 24, with none of the required ketene S,S-acetal 22 being observed.
- Moss, William O.,Jones, Annette C.,Wisedale, Richard,Mahon, Mary F.,Molloy, Kieran C.,et al.
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p. 2615 - 2624
(2007/10/02)
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