Remarkable Effect of Silyl Groups on Asymmetric Induction in a Conjugate Addition Reaction with O-Methylnorephedrine-Based N-Silylamidocuprates

Scalemic N-silylamidocuprates, prepared from O-methylnorephedrine in a two-flask procedure, are exceedingly reactive and give excellent enantiomeric excesses with chalcone, a classic substrate for studies of organocuprate conjugate addition. For example, the butyl N-diphenylmethylsilylamidocuprate (T = Bu) affords a 99.2% ee (99% yield) of (S)-3-butyl-1,3-diphenyl-1-propanone. The remarkably high yields with this and other silyl ligands are attributed to the extraordinary activating effect of a beta-silicon atom on organocuprate reactions. The high ee is a consequence of the larger size of the silyl ligands compared to that of the unsubstituted or methyl-substituted analogues.