Fesulphos ligand

Scheme 5.17 Pd-catalysed Diels-Alder reaction with Fesulphos ligands.

In 2005, Carretero et al. reported a second example of chiral catalysts based on S/P-coordination employed in the catalysis of the enantioselective Diels-Alder reaction, namely palladium complexes of chiral planar l-phosphino-2-sulfenylferrocenes (Fesulphos). This new family of chiral ligands afforded, in the presence of PdCl2, high enantioselectivities of up to 95% ee, in the asymmetric Diels-Alder reaction of cyclopentadiene with A-acryloyl-l,3-oxazolidin-2-one (Scheme 5.17). The S/P-bidentate character of the Fesulphos ligands has been proved by X-ray diffraction analysis of several metal complexes. When the reaction was performed in the presence of the corresponding copper-chelates, a lower and opposite enantioselectivity was obtained. This difference of results was explained by the geometry of the palladium (square-planar) and copper (tetrahedral) complexes. 

Scheme 5.19 Cu-catalysed aza-Diels-Alder reactions with Fesulphos ligand.

Scheme 10.12 1,3-Dipolar cycloadditions of azomethine ylides with polystyrene-supported Fesulphos ligand.

Scheme 10.72 Ring openings of meso heterobicyclic alkenes with Fesulphos ligands.

Carretero et al. already found that Pd(II) and Cu(I) complexes of P,S-bidentate ligands, especially those having a bulky substitution of sulfur, have provided very high asymmetric inductions. Recently, they have reported that Pd(II) complexes of chiral planar (R)-l-phosphino-2-sulfenylferrocenes (Fesulphos ligands) (62) act as effective Lewis acids for highly enantioselective Diels-Alder reaction (Scheme 16.19)... 

Azomethine ylides are typical 1,3-dipoles, their participation in [3+2]cycloaddition is greatly influenced by Cu catalysts. Asymmetric reactions are realized by the addition of chiral ferrocene ligands such as 141 (called Fesulphos) and 142. ... 

On the other hand, the use of the suitable combination of a metal salt, chiral ligand, and base promotes at low temperature the formation in situ of chiral A-metalated azomethine ylides from the corresponding iminoester and the subsequent selective cycloaddition onto the fullerene cage. Thus, the P,S chiral ligand Fesulphos along with copper(II) acetate directs the addition toward the formation of the stereoisomer (25, 55)-2-alkoxycarbonyl-5-arylpyrrolidino[3,4 l,2][60]fullerene with complete cis diasteroselectivity and enantiomeric excesses up to 93% (Scheme 34.9). 

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