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

classical techniques (Scheme 1.7) and the numerous methods available for the
enantioselective hydrogenation of dehydroarniw acids.
A number of methods exist for the generation of E- and 2-olefins, including
variations of the Wittig and Horner-Wadsworth-Ernrnons reactions. Among the most
versatile is the reaction of phosphonates 1.11 with various aldehydes to afford Cbz or
Boc protected deh ydroamino acids 1.12 with a preterence for 2-isomers (Scheme 1.7)?
Heck coupling of aryl iodides or bromides to 1.13 gives a-amido acrylates 1.14,
providing an alternative route to various aryl functionalized Z isomers. rhreo-BHydroxy-
a-arnino acids 1.15 cm be dehydrated into the E-isomer 1.16 providing complementarity
to the above methods.
O
Scheme 1.7
v c W n Ar(, Pd(OAcI2
NHBoc
NaHC03, Bu4NI,
DMF
NHBoc
The enantioselective hydrogenation of dehydroarnino acids 1.7 is generally
catalyzed by a chirally modified Wilkinson catalyst 1.17, and is such an efficient process
for the preparation of chiral amino acids that it is also used industrially (Scheme 1.8).