Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

Scheme 1.17
The chiral nickel (II) complex 1.39 reported by Belokon et al.. derived from
benzyl-proline, O-arninoacetophenone and glycine, is one of the best-studied systems for
glycine enolate derivatization. Alkyl halides,& aldehydes4' and 1,4-unsaiurated
carbonyls4' have al1 been added to 139 and enantioselectivities for addition are typically
in the order of 90% ee (Scheme 1.18). p-Hydroxy amino acid derivatives are generated
from aldehydes in good yield and with threo:allo ratios of >20: 1 in most cases, however,
poor induction of stereochemistry at the B-carbon is achieved with 1,4unsaturated
carbonyl compounds, for example, 2: 1 for methyl methacrylate (Section 4.1 -4.1).
1) base
*R"
Scheme 1.18
A wide variety of alkylating agents have been reacted with the enolate of 1.39 to
give alkylated a-amino acids in yields of 60-901 and generally >98% ee.'
Seebach and coworkers have developed the use of irnidazolidinones 1-41 prepared
from Ala, Met, Val, Phe> Asp and Glu." Deprotonation of the imidazolidinone
NH2