Asymmetric Synthesis of α,α-Disubstituted α-Amino Acids via Enantioselective Alkylation of Azlactones under Biphasic Conditions Using P-Spiro Chiral Tetraaminophosphonium Salts as a Phase-Transfer Catalyst
Enantioselective quaternization of 4-substituted oxazol-5-(4H)-ones using recoverable Cinchona-derived dimeric ammonium salts as phase-transfer organocatalysts
Dimeric anthracenyldimethyl-derived Cinchona ammoniumsalts are used as chiral organocatalysts (5 mol %) for the enantioselective 4-alkylation of 4-substituted azlactones. The corresponding adducts bearing a new quaternary center were obtained with up to 80% ee when using a dimericammonium salt derived from cinchonidine, and are precursors of α,α-disubstituted α-amino acids. The catalysts can be recovered
Asymmetric Synthesis of α,α-Disubstituted α-Amino Acids via Enantioselective Alkylation of Azlactones under Biphasic Conditions Using P-Spiro Chiral Tetraaminophosphonium Salts as a Phase-Transfer Catalyst
Highly enantioselective alkylation of azlactones derived from α-amino acids has been achieved under solid-liquid phase-transfer conditions using P-spiro chiral tetraaminophosphonium salt as a catalyst. The resulting alkylated azlactones can be readily converted into the corresponding α,α-disubstituted α-amino acids through simple acidic hydrolysis.
Palladium‐Catalyzed Asymmetric Decarboxylative Allylation of Azlactone Enol Carbonates: Fast Access to Enantioenriched α‐Allyl Quaternary Amino Acids
作者:Massimo Serra、Eric Bernardi、Giorgio Marrubini、Ersilia De Lorenzi、Lino Colombo
DOI:10.1002/ejoc.201801363
日期:2019.1.31
A practical synthetic protocol for the preparation of enantioenriched 4‐allyl oxazol‐5‐ones was developed. The key Pd‐catalyzed decarboxylative allylation allowed the attainment of the allylated derivatives in very good yields (83–98 %) and with ee up to 85 %. The corresponding quaternary amino acids can be recovered in their enantiopure form or in high optical purity after a single recrystallization