Enantioselective syntheses O 0031First Application of Chiral Ionic Liquids in Asymmetric Baylis-Hillman Reaction. -The use of a chiral ionic liquid [cf. (I)] based on N-alkyl-N-methylephedrinium salts as the reaction medium for the Baylis-Hillman reaction produces the adducts (IV) with low e.e. -(PEGOT, B.; VO-THANH*, G.; GORI, D.; LOUPY, A.; Tetrahedron Lett. 45 (2004) 34, 6425-6428; Lab. React. Sel. Supports, CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.; Eng.) -Mais 48-029
Imidazole derivatives R 0190Amino Acid Homologation by the Blaise Reaction: A New Entry into Nitrogen Heterocycles. -Treatment of Cbz-protected amino nitriles of type (IV) derived from α-amino acids with bromoacetate and subsequent base-mediated cyclization provides a new approach to imidazolidinones like (VI). These compounds smoothly undergo stereoselective reduction to give cis-and/or trans-substituted imidazolidinones. Hydrolysis of the latter does not yield the expected β,γ-diamino acids but cyclization products like (IX) and (X). Blaise reaction of the functionalized amino nitrile (XIII) provides the lactam (XIV) instead of the corresponding imidazolidinone. (XIV) undergoes stereoselective reduction giving the trans-substituted lactam (XV). -(HOANG, C. T.; BOUILLERE, F.; JOHANNESEN, S.; ZULAUF, A.; PANEL, C.; POUILHES, A.; GORI, D.; ALEZRA*, V.; KOUKLOVSKY, C.; J.
Frozen: The spontaneous crystallization of an achiral compound in a chiral conformation is used as the unique source of chirality in an absolute asymmetric synthesis of tertiary amino acids. The dynamic axial chirality of tertiary aromatic amides is frozen in a crystal (see picture) and is responsible for the stereoselectivity of the deprotonation/alkylation (see scheme). α‐Amino acid derivatives are synthesized in up to 96 % ee.
Absolute Asymmetric Synthesis of Tertiary α-Amino Acids. -The first example for the use of the frozen-chirality approach for the synthesis of biologically interesting compounds, e.g. amino ester (VIII), is presented. For practical reasons the enantiomer (S)-(V) with the shortest retention time is used for the transformation to (VIII). -(MAI, T. T.; BRANCA, M.; GORI, D.; GUILLOT, R.; KOUKLOVSKY, C.; ALEZRA*, V.; Angew. Chem., Int. Ed. 51 (2012) 20, 4981-4984, http://dx.doi.org/10.1002/anie.201200950 ; Lab. Chim. Procedes Subst. Nat., Univ. Paris Sud, F-91406 Orsay, Fr.; Eng.) -C. Gebhardt 40-149
Substrate Control in Enantioselective and Diastereoselective Aldol Reaction byMemory of Chirality: A Rapid Access to Enantiopure -Hydroxy Quaternary -Amino Acids. -An asymmetric aldol reaction memorizing the underlying chirality of the starting amino acid is reported for the first time. Using L-alanine-derived oxazolidinone (I) as starting material, the initial chirality is memorized through the dynamic axial chirality of the tertiary aromatic amide. Moreover, a surprising diastereoselectivity control from the aldehyde side is observed. Finally, diastereopure and enantioenriched -hydroxy quaternary -amino acids like (XI) become accessible. -(VISWAMBHARAN, B.; GORI, D.; GUILLOT, R.; KOUKLOVSKY, C.; ALEZRA*, V.; Org. Lett. 16 (2014) 3, 788-791, http://dx.doi.org/10.1021/ol403523e ; Inst. Chim. Mol. Mater., Univ. Paris-Sud, F-91405 Orsay, Fr.; Eng.) -H. Haber 29-149
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