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

in 4165% yields with 63-96% diastereoselectivity in preference of the syn (threo)
Myers et al. have recently reported the use of a pseudoephedrine derivative 1.44
as a chiral auxiliary in the synthesis of various allcylated a-amino acids? The
advantages of this template include ease of preparation, high ee and de's and simplicity
of hydrolysis off the template. The reported yields ranged between 70-805 for
intermediate 1.45 and hydrolysis gives the fiee a-amino acids in generally >85% yield,
however, few reports currently exist utilizing this methodology (Scheme 1.20).
Scbeme 1.20
1.44 R=Me, Et. allyi, Bn 1.45
1 J.3.2 Glycine a-Cation Equivalents
Many of the cyclic chiral templates described in the previous section can be
converted to a-cation equivalents simply by the introduction of good leaving groups at
the a-position. This approach has been used successfully with Schollkopf's bis-lactim
1.33, Williams' oxazinone 1.34 and Belokon's Ni-complex 1.39.
The chlorinated derivative of bis-lactim ether 1.33 was converted into aromatic a-
amino acids by Friedel-Crafts alkylation with yields in the 60% range and
enantioselectivites generaily >90% ee and occurs with inversion of stereochemistry at the
a-carbon ."