New auxiliaries for copper-catalyzed asymmetric Michael reactions: Generation of quaternary stereocenters at room temperature

Dialkyl amides of L-valine, L-isoleucine, and L-tert-leucine (2) are excell ent chiral auxiliaries for the construction of quaternary stereocenters at ambient temperature. Enaminoesters 3, prepared from these auxiliaries 2 and Michael donors 1, undergo a copper-catalyzed asymmetric Michael reaction w ith methyl vinyl ketone (MVK, 4) to afford products 5 in 70-90% yield and 9 0-99% ee (enantiomeric excess). The exclusion of moisture or oxygen is not necessary. The auxiliaries 2 are readily available by standard procedures. After workup they can be recovered almost quantitatively.