The alkylation of 7 occurs in moderate to good trans stereoselection (d.e.40-98%), while a poorer d.e. (40-98%) is observed for 8. On the contrary, in both substrates the alkylation with CH3I produces a greater amount of the cis isomer (d.e.48%).). Cleavage of the lactims 9(a,e) gives enantiomerically pure dipeptides 14(a,e). The absolute configuration of the introduced stereogenic centres has been assigned on the basis of the 1H-NMR data in connection with the conformational analysis.
Favero, Valentina,Porzi, Gianni,Sandri, Sergio
p. 599 - 612
(2007/10/03)
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