ZnF2--chiral diamine complex

In 1996, Carreira reported a catalytic enantioselective aUylation of aldehydes using BlNOL-modified Tip4. More recently, Kobayashi reported a catalytic enantioselective aUylation of hydrazono esters in aqueous media using ZnF2-chiral diamine complex, [Eq. (13.36)]. In both reactions, reaction mechanism via dual activation of the substrate by Lewis acid metals and aUylsUanes by fluoride is proposed ... 

Catalytic enantioselective allylation of a-hydrazono esters with allyltrimethoxysilanes in aqueous media can be accomplished by ZnF2-chiral diamine complexes.132... 

As for the reaction mechanism, some experimental evidence suggests that the ZnF2-chiral diamine complex is the real catalytic active species and that it is regenerated from MejSiF that forms as the reaction progresses (Scheme 15.22, fluoride-catalyzed mechanism). 

ZnX2," " ZnCl2," ° Zn(0Tf)2-H20," ZnF2 with diamine complex,- Et2Zn with (S, S) linked BINOL,dinuclear zinc catalyst," chiral zirconium catalyst" (e.g., Zr(0-... 

Quite recently, chiral diamine ligands have been used by Kobayashi et al. for highly enantioselective Mannich-type reactions [228, 229]. The chiral complex prepared from chiral diamine 89a and Cu(OTf)2 effects highly enantioselective addition of silyl enolates to a-N-acyhmino esters (Scheme 10.82) [228]. The first example of catalytic asymmetric Mannich-type reaction in aqueous media has been achieved by the combined use of ZnF2, diamine 89b, and TfOH in the reaction of a-hydrazono esters [229]. 

---