Enolates in asymmetric synthesis

The utility of chiral oxazoline enolates in asymmetric synthesis has elegantly been demonstrated by Myers (106,120). The stereoselective aldol condensations of these enolates have been examined in a hmited number of cases (eq. [107]) (32,121). Assuming that the enolate formed has the geometry indicated in 164 (120b), the diastereoselection observed for both the aldol condensation and the previously reported alkylations favors electrophile attack on the Re face as indicated. In contrast, the unsubstituted enolate 163b exhibits significantly poorer diastereoface selection with a range of aldehydes (eq. [108]) (121). 

In fact, the usefulness of chiral oxazoline enolates in asymmetric synthesis had been already demonstrated by Meyers [24]. Evans obtained enantiofacial selectivities (or enantiomeric excesses = e.e) equal to or greater than 99% (Table 9.4). 

D. A. Evans, Stereoselective Alkylation Reactions of Chiral Metal Enolates, in Asymmetric Synthesis -Stereodifferentiating Reactions, Part B (J. D. Morrison, Ed.), Vol. 3, 1, AP, New York, 1984. 

---

See also in sourсe #XX -- [ , , ]

---