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

hydrolysis of the L-threo-B-phenylserine derivative was reported, giving the €tee amino
acid in 54% yield and 92:8 threo:erythro ratio with an overall yield of 4646 from the
imidazolidinone template 1.42.
Scheme 2.12
Another imidazolidinone-bound enolate 2.31, described by Craddick et al., has
been shown to undergo aldol condensations with aliphatic and aromatic aldehydes in
good yield (62-841) and high stereocontrol(93-95% de) (Scheme 2.1 3)'3
Scheme 2.13
Belokon et al. have successfully used the chiral nickel (II) complex 1.39 in the
synthesis of threo-P-hydroxy-a-arnino acids usually with diastereoselectivities >30: 1 and
yields of 55-87% (Scheme 2.14)."
Unlike the glycine enolaîes described above, Evans' methodology provides access
to boih syn and anti diastereomers. &Phenylserine was synthesized in 50% overall yield
with >98% de in the stereocenter forming reactions (Scheme 2. lS)."