- Application of the Mitsunobu reaction to ephedrines and some related amino alcohols. Aspects of intramolecular participation of the amino group
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Inversion of configuration at the benzylic hydroxyl group of (1S,2S)-pseudoephedrine (2) to afford (1R,2S)-ephedrine is known to be a difficult process.The Mitsunobu reactions of 1 and 2 might offer a route to achieve such inversions.In fact Mitsunobu reactions on 1 and 2 are known to proceed via aziridines formed on intramolecular SN2 substitution by the amine functionality.The Mitsunobu reactions of N-methylated and N-benzylated ephedrines have been found to proceed via the corresponding aziridinium ions.These aziridinium ions can be opened (SN2 substitution) by nucleophiles like phthalimide and thiols.Intramolecular participation in 2 can be avoided by use of the tert-butyloxycarbonyl-(BOC) or benzyloxycarbonyl- (CBZ) protected derivatives.Mitsunobu reactions on these derivatives lead to inversion of configuration at the benzylic hydroxyl center.In contrast the BOC and CBZ derivatives of 1 are deprotected under Mitsunobu conditions.The Mitsunobu reactions of threo (1S,2S)-2-amino-1,3-propanediol have also been examined.An attempt to achieve protection by reaction with dimethylformamide dimethyl acetal led to the more substituted 2-oxazoline as established by X-ray crystallography.The desired inversion of configuration of the benzylic hydroxylic group was eventually achieved by protection of the amino substituent as the phthalimide and protection of the primary hydroxyl group as the tosylate.
- Poelert, Martin A.,Hulshof, L. A.,Kellogg, Richard M.
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p. 355 - 364
(2007/10/02)
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- Reactions of (-)-Ephedrine, (+)-Norpseudoephedrine and Derivatives with N,N-Dimethylacetamid-dimethylacetal and N,N-Dimethylformamid-dimethylacetal
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The reactivity of (-)-ephedrine (2) and (+)-norpseudoephedrine (3) towards the amid-acetals 1 a/b has been studied.Both 2 and 3 were acetylated resp. formylated at first at the amino group.Nevertheless, derivatives of 2 and 3 possessing a trisubstituted amino group react with 1 a in a sigmatropic rearrangement to ortho substituted dimethylcarbamoylmethyl derivatives.By subsequent reduction with lithiumaluminiumhydride the aromatic compounds 8, 13, and 18 with two aminoethyl groups are easily available.In contrast to these results 1 b did not furnish any rearrangement products. Keywords. (-)-Ephedrine; (+)-Norpseudoephedrine; N,N-Dimethylacetamid-dimethylacetal; N,N-Dimethylformamid-dimethylacetal; Sympathomimetic effects; Sigmatropic rearrangements.
- Koehl, M,Spreitzer, H.,Fleischhacker, W.
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p. 911 - 918
(2007/10/02)
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- MISE EN EVIDENCE PAR RMN-(1)H ET -(13)C D'ISOMERISME Z/E ET D'EQUILIBRE CONFORMATIONNEL SUR UNE SERIE DE DERIVES MONO- ET DIACETYLES DE 2-ALKYLAMINO-1-PHENYLPROPAN-1-OLS
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(1)H- and (13)C NMR studies of mono- and diacetylated-erythro- and threo-2-alkylamino-1-phenylpropan-1-ols, C6H5CHOHCHNHRCH3 (R = H, CH3, C2H5 AND i-C3H7) show that the series exhibit Z/E isomerism about the C-N amide bond.The Z/E ratio increases in the monoacetylated series CH3 1-C2 and N-C2 bonds.In the Z configuration, the conformer Z-s-syn where the proton H-2 is syn with the N-alkyl substituent predominates.
- Tytgat, D.,Gelbcke, M.
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p. 479 - 490
(2007/10/02)
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