Taniaphos-based ligands

Riant employed other chiral Taniaphos-based ligands to induce chirahty in Cu(l)-catalyzed reductive aldol reactions of aldehydes 92 with methyl acrylate 127 using phenylsilane as a reducing agent. Although the reaction was highly chemoselective. 

Sammakia and Uemara, the development of the 1,5-bisphosphine Taniaphos by Knochel and coworkers, and more recently by Fu for the preparation of chiral heterocycles, ferrocene-based ligands in asymmetric catalysisJ For a specialized recent review concerning apphcations of chiral ferrocene ligands in asymmetric catalysis, the reader may consult a review by Carretero et alP ... 

The ferrocene-based ligand Taniaphos (137) has been found particularly effective in copper-catalyzed AAA using Grignards and allylic bromides. " Here, CuBr SMe2 is the precursor of choice (1-5 mol%), used in DCM at -78 "C. Cinnamyl systems typically react in high yields and excellent ee s. Catalyst loading of only 1% is sufficient. Reactions in MTBE (f-BuOMe) as solvent were not as selective. 

High ees were achieved recently with Cu-JOSIPHOS complexes for the Michael addition of Grignard reagents to various substrates (302). Another ferrocene-based ligand, TANIAPHOS, was also efficient in the copper-catalyzed reductive addition of aldehydes and ketones to methyl acrylate (303). 

A series of non-f, -symmetrical ferrocene-based 1,5-diphosphane ligands (TaniaPhos) has been developed by Knochel.88,88a,88b The ligands have been effectively used in Rh- or Ru-catalyzed asymmetric hydrogenations. The ligand 39, which has an MeO group at the chiral carbon center, has shown excellent applications in the hydrogenation of several olefin and ketone substrates.89 Weissensteiner and Spindler have reported a series of structurally different... 

Many chiral ferrocene-based bisphosphane ligands with great structural variations have been developed recently. Togni and Spindler introduced non-Crsymmetric ferrocene-based Josiphos type ligands. Josiphos 38 has been found to be effective for Rh-catalyzed hydrogenation of a-acetamidocinnamate, dimethyl itaconate, and P-keto esters. A class of non-Cj-symmetrical ferrocene-based 1,5-diphosphane ligands (TaniaPhos 39) has also been... 

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