- Synthesis of α-trifluoromethyl substituted α-amino acid derivatives from methyl 3,3,3-trifluoro-2-diazopropionate
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New derivatives 2-7 of α-trifluoromethyl substituted amino acids are synthesized via transformation of ammonium ylides formed on reaction of methyl 3,3,3-trifluoro-2-diazopropionate with amines and amides, respectively.
- Osipov, Sergey N.,Sewald, Norbert,Kolomiets, Alexey F.,Fokin, Alexander V.,Burger, Klaus
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- The 'non-oxidative' Pummerer reaction: Conclusive evidence for S(N)2- type stereoselectivity, mechanistic insight, and synthesis of enantiopure L- α-trifluoromethylthreoninate and D-α-trifluoromethyl-allo-threoninate
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Enantiopure methyl D-α-trifluoromethyl-allo-threoninate 18 and L-α- trifluoromethylthreoninate 19 were synthesized using (R)-ethyl p- tolylsulfoxide as chiral α-hydroxyethyl anion equivalent. The key step was the S(N)2-type replacement of the sulfinyl auxiliary with a hydroxy group, via trifluoroacetic anhydride promoted 'non-oxidative' Pummerer reaction (NOPR) of the diastereomeric intermediate β-sulfinyl amines 14 and 15, obtained by condensation of (R)-ethyl p-tolylsulfoxide 13 with the N-Cbz imine of methyl trifluoropyruvate 12. The conclusive evidence for S(N)2-type stereoselectivity of the NOPR was achieved by X-ray diffraction of both the starting diastereomer 14 and the p-bromobenzoate 25, obtained from the threoninate 19. NMR monitoring of the NOPR performed on 15 allowed the detection of a transient intermediate, which was identified as the four membered cyclic σ-sulfurane 27. This intermediate spontaneously rearranged (40 min, rt) into the corresponding sulfenamide 17, probably via an intramolecular displacement of the sulfinyl by a trifluoroacetoxy group, with inversion of configuration at the carbon stereocenter. The same process occurred for the diastereomeric β-sulfinyl amine 14, but the sulfenamide 16 was formed at very fast rate, thus precluding NMR detection of the corresponding σ-sulfurane intermediate 26. One-pot treatment of the diastereomeric sulfenamides 16 and 17 with NaBH4 afforded very good yields of the corresponding threoninates 18 and 19.
- Crucianelli, Marcello,Bravo, Pierfrancesco,Arnone, Alberto,Corradi, Eleonora,Meille, Stefano V.,Zanda, Matteo
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p. 2965 - 2971
(2007/10/03)
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- New Synthetic Pathways to 3,3,3-Trifluoroalanine, 2-Deutero-3,3,3-trifluoroalanine and their Derivatives
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New synthetic pathways to 3,3,3-trifluoroalanine, 2-deutero-3,3,3-trifluoroalanine, their esters, amides, and thioamides are described, starting from hexafluoroacetone, and trifluoropyruvates, respectively.
- Burger, Klaus,Hoess, Eva,Gaa, Karl,Sewald, Norbert,Schierlinger, Christian
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p. 361 - 384
(2007/10/02)
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- FLUORINE-CONTAINING AMINO ACIDS. A CONVENIENT METHOD FOR THE SYNTHESIS OF D,L-β,β,β-TRIFLUOROALANINE
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A convenient method was developed for the synthesis of D,L-β,β,β-trifluoroalanine by the Curtius transformation on methyl 3,3,3-trifluoro-2-fluoroformylpropionate with sodium azide or trimethylsilyl azide.The presence of small amounts of hydrogen fluoride
- Yagupol'skii, Yu. L.,Soloshonok, V. A.,Kukhar', V. P.
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p. 459 - 463
(2007/10/02)
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