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

increasing the steric bulk on the amine, protecting it as the P W n derivative 5.11
(P=PhFl, Bn, R'=~Bu, R~=M~).*~
Baldwin and coworkers approached the moderate stereoselectivity previously
reported by his group through the use of azetidinone 5.13 (Scheme 5.7)? Stereospecific
"antz" allylation was achieved in >95% in 95% yield. The substituted azetidinone 5.14
was opened with O-benzylhydroxylamine to give the 2S,3R derivative en route to the
synthesis of alahopcin 5.2? Hanessian et al. used the same methodology to synthesize p-
methylaspartate 5.1 by hydrolyzing 5.14 @=Me) with 6N HCl?
L-AS, -
Scheme 5.7
- 2) E+
O *H 98%
ee.
The first report of the general addition of heteroatoms at the B-position of
aspartate was by Sardina et al. in 1992? Using Rapport's PhFl protected aspartic acid
derivative 5.11 (P=PhFi, R'=~Bu,M~, R~=M~), the enolate was quenched with solid
MoOPH to give the p-hydroxyaspartate derivative 5.12 (P=PhFl, R'=~Bu,M~, R*=M~,
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