Schiff base dinuclear catalyst

On the other hand, a dinuclear chiral nickel catalyst, (R)-3, was developed by Mitsunuma and Matsunaga to promote the conjugate addition of a-sub-stituted p-keto esters to nitroethylene. " As shown in Scheme 2.6 the use of 1-10 mol% of this Schiff base dinuclear catalyst in a mixture of EtOAc and toluene as solvent allowed a range of cyclic as well as acyclic p-keto esters to be added to nitroethylene, providing the corresponding chiral Michael products in moderate to almost quantitative yields (73-92%), combined with good to high enantioselectivities of up to 98% ee in the case of cyclic substrates, and... 

On the other hand, Matsunaga and Shibasaki have observed an opposite syn diastereoselectivity in the enantioselective conjugate addition of a-keto anilides to nitroalkenes under dinuclear nickel catalysis. Indeed, the use of 10 mol% of dinuclear chiral Schiff base nickel catalyst 9 in the presence of HFIP and 5 A MS as additives in 1,4-dioxane as solvent allowed the corresponding Michael adducts to be achieved in moderate to good yields, with good syn diastereoselectivities of up to >90% de and combined with good to excellent enantioselectivities of up to 98% ee (Scheme 2.15). The substrate... 

The Schiff bases (23), (43), and (44) formed Mo complexes of the type cw,wgr-[Mo02(ligand)] (which was associated in the solid state) and cw,mer-[Mo02(ligand)L] (L = neutral donor). The structures, electrochemical and chemical properties of these complexes, and their oxygen-atom transfer capabilities were extensive studies. These species were generally more active catalysts than their N-O-O-donor atom Schiff base counterparts, but oxygen-atom abstraction reactions with tertiary phosphines led to dinuclear Mo species rather than monomeric Mo complexes. 

Scheme 6.13 a-Aminations of iV-Boc-oxindoles with Schiff base mononuclear and dinuclear nickel catalysts. 

Scheme 8.1 Aldol reaction of formaldehyde with P-keto esters in the presence of a preformed dinuclear nickel catalyst derived from a Schiff base ligand.

On the other hand, Mannich-type reactions of homoenolates or their synthetic equivalents for the production of y-amino acids have been less studied than those involving enolates. In this context, the same authors applied a closely related preformed dinuclear nickel catalyst derived from Schiff base ligand 8 to induce the asymmetric direct Mannich-type reaction of a-keto anilides with o-Ns-protected imines (Scheme 8.11). The corresponding... 

---