A practical asymmetric synthesis of a-methyl a-amino acids using a chiral Cu–salen complex as a PTCDOI:
10.1016/S0040-4039(00)01247-8
AbstractThe asymmetric C-alkylation of N-benzylidene alanine methyl ester has been achieved using a copper(II) (salen) complex as an asymmetric phase transfer catalyst and provides a practical synthesis of a-methyl a-amino acids with up to 86% enantiomeric excess.
Tetrahedron Letters
Volume 41, Issue 37 , September 2000, Pages 7245-7248
Other PTC ReactionsDOI:
10.1016/S0957-4166(99)00185-8
AbstrctEnantiopure 2-hydroxy-2'-amino-1,1'-binaphthyl (NOBIN) is shown to catalyse C-alkylation of aldimine Schiff's bases of alanine ester under phase-transfer catalysis conditions (solid NaOH or NaH, toluene, ambient temperature, 10% NOBIN). Using (R)-NOBIN, the final (S)-a-methylphenylalanine was obtained in up to 68% ee.
DOI:
10.1016/S0957-4166(98)00044-5
AbstrctCompound (4R,5R)- or (4S,5S)-2,2-dimethyl-a,a,a',a'-tetraphenyl-1,3-dioxolane-4,5-dimethanol (TADDOL) was shown to catalyze C-alkylation of aldimine Schiff's bases of alanine esters under phase-transfer catalysis conditions (solid NaOH, toluene, ambient temperature, 10% TADDOL) with the e.e. of the final a-methylphenylalanine or a-allylalanine reaching 82%.
DOI:
10.1016/S0040-4039(99)01836-5
AbstractApplication of N-anthracenylmethyl dihydrocinchonidinium bromide as a catalyst for the enantioselective alkylation of a series of alanine-derived imines is reported. Using solid K2CO3/KOH as the stochiometric base such alkylations can be achieved with enantiomeric excesses up to 87% allowing rapid access to a,a-dialkyl-a-amino acid esters.
I am mainly interested in the Copper salen reaction, but the other PTC's wouldn't bother me if they weren't so exotic. Can someone explain to me chiral Cu-Salen complexes? There was another interesting one that I couldn't access the abstract to, titled........ "Asymmetric PTC C-Alkylation Catalyzed by Chiral Derivatives of Tartaric Acid and Aminophenols" found on Beilstein, J.Org.Chem. , Jan 2000.
