Inductive effect from functional groups, Table

Table 4.7 Inductive effects from functional groups...

The favorable effect of the enamide function on asymmetric induction is indicated not only by the result with compound I, but also by later results summarized in Table I, where optical purities in the range of 70 to 80% were generally obtained for various derivatives of alanine, phenylalanine, tyrosine, and 3,4-dihydroxyphenylalanine (DOPA). The Paris group found that the Rh-(-)-DIOP catalyst yielded the unnatural R or d -amino acid derivatives, whereas l-amino acid derivatives could be obtained with a (+)-DIOP catalyst. Since the optical purity of the IV-acylamino acids can often be considerably increased by a single recrystallization (fractionation of pure enantiomer from racemate) and the IV-acetyl group can be removed by acid hydrolysis, this scheme provides an excellent asymmetric synthesis route to several amino acids. 

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