Amino acidsAmino acids U 0400Catalytic, Asymmetric Synthesis of α,α-Disubstituted Amino Acids. -The asymmetric alkylation of enolates derived from N-benzylidene amino acids esters is investigated in the presence of copper(salen) as the catalyst. The reactivity of the substrates decreases sharply with the steric demand of the substituent. Generally, the absolute configuration of the product cannot be determined. -(BELOKON', Y. N.; BHAVE, D.; D'ADDARIO, D.; GROAZ, E.; MALEEV, V.; NORTH*, M.; PERTROSYAN, A.; Tetrahedron Lett. 44 (2003) 10, 2045-2048; Dep. Chem., King's Coll., London WC2R 2LS, UK; Eng.) -Mais 22-201
Copper(II)salen Catalyzed, Asymmetric Synthesis of α,α-Disubstituted AminoAcids. -The chiral Cu(II)-salen complex is shown to be a useful phase-transfer catalyst for the asymmetric α-alkylation of α-amino acid-derived enolates in the system solid NaOH-toluene. The enantioselectivity decreases with increasing steric bulk around the α-position. Thus, good results are achieved with the enolates of α-aminobutanoic ester (Ia) and leucine ester (VI), while the valine-derived enolate (XX) remains unchanged under the applied reaction conditions. The application of functionalized amino acid enolates like aspartic acid derivative (Id) or allylglycine derivative (XI) is possible, but an unexpected lactonization reaction is observed for glutamic acid derivative (XVIII). The use of functionalized α,α-disubstituted amino acid esters (XI) is demonstrated in the synthesis of non-natural amino acid derivative (XVII). -(BELOKON, Y. N.; BHAVE, D.; D'ADDARIO, D.; GROAZ, E.; NORTH*, M.; TAGLIAZUCCA, V.; Tetrahedron 60 (2004) 8, 1849-1861; Dep. Chem., King's Coll., London WC2R 2LS, UK; Eng.) -Mischke 22-198 2004 Amino acids
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