- Reactivity and Enantioselectivity in the Reactions of Scalemic Stereogenic α-(N-Carbamoyl)alkylcuprates
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Stereogenic 2-(N-carbamoyl)pyrrolidinylcuprates prepared from scalemic (i.e., enantioenriched) N-Boc-2-lithiopyrrolidine and THF soluble CuCN·2LiCl react with vinyl iodides, vinyl triflates, β-iodo-α,β-enoates, propargyl mesylates, and allyl bromide to afford the substitution products with excellent enantioselectivity. Excellent enantiomeric ratios are obtained in the conjugate addition reactions with methyl vinyl ketone while low enantiomeric ratios can be achieved with acrylate esters using HMPA/TMSCl activation. Enantiomeric ratios vary with substrate substitution patterns and the observed enantioselectivities appear to be more a function of cuprate-electrophile reactivities than of the reaction type (e.g., substitution, conjugate addition). Low enantiomeric ratios are obtained with the α-(N-carbamoyl)benzylcuprates. The lithium-copper transmetalation and cuprate vinylation reactions proceed with retention of configuration.
- Dieter, R. Karl,Oba, Gabriel,Chandupatla, Kishan R.,Topping, Chris M.,Lu, Kai,Watson, Rhett T.
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p. 3076 - 3086
(2007/10/03)
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- Asymmetric syntheses of N-Boc 2-substituted pyrrolidines and piperidines by intramolecular cyclization
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Asymmetric lithiation-substitutions by n-BuLi/(-)-sparteine with the N- Boc-N-(3-halopropyl)allylamines 1-4 provide the N-Boc-2-alkenylpyrrolidines (S)-5, (S)-6, and (S)-7 in yields of 3193% with enantiomeric ratios (ers) from 65:35 to 90:10. These reactions are shown to involve an initial asymmetric deprotonation, but the enantiodetermining step is a subsequent asymmetric cyclization under the influence of the chiral ligand. Extension to formation of a piperidine is illustrated by reaction of N-Boc-(4- chlorobutyl)cinnamylamine (9) to afford (S)-N-Boc-2-(trans-β- styryl)piperidine ((S)-10) in 68% yield with an enantiomeric ratio (er) of 84:16. Analogous reactions with epoxide ring openings of N-Boc-N- (oxaalkenyl)benzylamines 11 and 12 afford the corresponding N-Boc-2-phenyl- 3-(hydroxymethyl)pyrrolidine (13) in 67% yield with a diastereomeric ratio (dr) of 50:50 and ers of 97:3 and 95:5 and the corresponding N-Boc-2-phenyl- 3-(hydroxymethyl)piperidine (14) in 29% yield with a dr of 86:14 and ers of 81:19 and 86:14.
- Serino,Stehle,Yong Sun Park,Florio,Beak
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p. 1160 - 1165
(2007/10/03)
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- Synthesis of Chiral Bicyclic Lactams Using Ring Closure Metathesis: Synthesis of (-)-Coniceine and (S)-Pyrrolam A
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Chiral (-)-coniceine and (S)-pyrrolam A were synthesized from dienes prepared from L-proline by ring closure metathesis.
- Arisawa, Mitsuhiro,Takezawa, Emiko,Nishida, Atsushi,Mori, Miwako,Nakagawa, Masako
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p. 1179 - 1180
(2007/10/03)
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