DuPHOS hgand

Significant advance in the field of asymmetric catalysis was also achieved with the preparation of l,2-bis(phospholano)benzene (DuPHOS 4) and its confor-mationally flexible derivative (l,2-bis(phospholano)ethane, known as BPE) by Burk et al. [59]. Two main distinctive features embodied by these Hgands, as compared to other known chiral diphosphine ligands, are the electron-rich character of the phosphorus atoms on the one hand and the pseudo-chirality at phosphorus atoms, on the other. These properties are responsible for both the high activity of the corresponding metal complex and an enantioselection indepen-... 

The hydrogenation of a series of T/Z-isomeric mixtures of a-arylenamides containing a MOM-protected /9-hydroxyl group, using BICP-Rh and Me-DuPhos-Rh catalysts, affords the /9-amino alcohol derivatives with excellent enantioselectivity [41c]. A 1,4-di-phosphane, T-Phos, with a rigid 1,4-dioxane backbone is also a very effective Hgand for this transformation (Eq. 11) [45]. 

A copper-catalyzed reaction using a chiral diphosphine hgand, DuPHOS, with an added lanthanide salt, provides good levels of enantioselectivity (67-91% ee) in additions of the simple allylboronate 31 to both aromatic and aliphatic ketones that present a large difference of steric bulk on the two sides of the carbonyl group. One such example is shown in Eq. 81. On the basis of B NMR experiments and on the lack of diastereoselectivity in crotylation reactions, the... 

A new family of chelating diphosphines, where phosphorus is part of a five-membered ring containing two asymmetric centers, was developed at Du Pont by Burk et al. in 1990 [58a]. These C2-symmetric Hgands (duphos and derivatives) gave excellent rhodium catalysts for asymmetric hydrogenation of many types of imsatuxated systems. 

An intramolecular version of the reaction has been reported by the same group with the boronated version of 56 (Scheme 6.25, Section 6.2.3.1, with Me-BPE or Me-DuPhos as hgands and a proton sponge instead of NaSiOMc3) to avoid displacement of the diphosphine in the catalyst. For R = Cy and (-)-Men no eyelisation was observed but for R = Ph the expected reaction occurred to yield the benzophospholanes borane in 60-89% yield with ee up to 70% with Me-DuPhos. 

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