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

Inverse addition was used to generate the dianion (based on results described in chapter
5) and addition of electrophile were both carried out at -78'C to prevent decomposition
of the enolate and erosion of diastereoselectivity which occurred upon warming to -30°C.
Methyl iodide was chosen as the alkylating agent since an easily identifiable doublet
would be formed which could be integrated by NMR methods to determine
diastereoselectivity .
At first, &ter generation of the enolate and addition of methyl iodide. the y-
methylglutamate 4.73 denvative was seemingly generated in approximately 10: 1 ratio
based upon 'H-NMR intcgration of the new methyl group at 61.15 ppm (Figure 4.2)
although no other signals comsponding to the other diastenomer were observed. High
field NMR analysis (2 300 MHz) was essential since examination of the methyl doublets
on lower field instruments failed to distinguish between diastereomers (vide infra). In