Bisphosphinic acids

By analogy with bisphosphonates, bisphosphinic acids were recently synthesized for their complexing abilities (Scheme 63) [228]. The synthesis was... 

Much effort has been placed in the synthesis of compounds possessing a chiral center at the phosphoms atom, particularly three- and four-coordinate compounds such as tertiary phosphines, phosphine oxides, phosphonates, phosphinates, and phosphate esters (11). Some enantiomers are known to exhibit a variety of biological activities and are therefore of interest Oas agricultural chemicals, pharmaceuticals (qv), etc. Homochiral bisphosphines are commonly used in catalytic asymmetric syntheses providing good enantioselectivities (see also Nucleic acids). Excellent reviews of low coordinate (coordination numbers 1 and 2) phosphoms compounds are available (12). 

This approach makes use of bromopropyl phosphine 17 as a key synthon obtained via the reduction of 3-bromopropyl phosphonate with dichloroaluminum hydride [10]. Reaction of bromopropyl phosphine 17 with the dianion of 6,8-dithiooctanoic acid produced the -COOH functionalized P2S2-primary bisphosphine framework 18 in > 80% yields (Scheme 7) [10]. 

Arylation of alkynes via addition of arylboronic acids to alkynes represents an attractive strategy in organic synthesis. The first addition of arylboronic acids to alkynes in aqueous media catalyzed by rhodium was reported by Hayashi et al.89 They found that rhodium catalysts associated with chelating bisphosphine ligands, such as 1,4-Ws(diphenyl-phosphino)butane (dppb) and 1,1 -/ E(diphenylphospliino)fcrroccnc... 

Fig. 2. Drawing showing the bisphosphine- rhodium complex viewed along the plane of the five-membered ring (diene omitted), and the Z-a-benzamido cinnamic acid substrate in a linear and flat conformation.

Hydroxy-phosphines undergo benzoylation with o-sulfobenzoic anhydride in the presence of bases (Na2C03 or BuLi) affording sulfobenzoylated phosphine products. In such a way several mono- and dihydroxy phosphines could be made soluble in water, exemplified by the chiral bisphosphines 53. It should be noted, that this general method allows the preparation of water-soluble sulfonated derivatives of acid-sensitive phosphines, such as DIOP, too, which are not accessible via direct sulfonation [56]. 

Pye and Rossen have developed a planar chiral bisphosphine ligand, [2.2]PHANE-PHOS, based on a paracyclophane backbone (Scheme 1.6) [69]. Moreover, the ortho-phenyl substituted NAPHOS ligand, Ph-o-NAPHOS, has been successfully applied for the rhodium-catalyzed hydrogenation of a-dehydroamino acid derivatives [70]. 

Over the past decade we have explored a number of phosphine ligands for incremental improvements of present systems and for studies in new types of reductions and hydroformylations. Even though bisphosphines continue to dominate the field, we have found fairly efficient monophosphines. This chapter deals with these and other systems that we have explored for a-phenylacrylic acid, dehydrovaline, and hydroformylation of vinyl acetate. Even though we have not solved efficiently any of these cases, we ve learned a lot about the behavior of a variety of ligands and hope that this knowledge will contribute to these and other unsolved problems in this field. 

This in situ catalyst is suitable for reducing acids which provide a proton source to release the AcAc. When reducing neutral substrates, one must either add. 005 mmol of HC1 or use a preformed solid catalyst of the type [Rh(COD)(Bisphosphine)]+ BF4 (3). 

A rhodium-catalysed asymmetric 1,4-addition of arylboronic acids to substituted maleimides (198) has been described. The regioselectivity in this reaction is controlled by the choice of ligand (dienes or bisphosphines) 1,4-adducts with a quaternary stere- ocentre (199) can be obtained with high regioselectivity (87%) and enantioselectivity (<97% ee) when (7 )-H8-BINAP is employed as ligand.245... 

Enantioselective reduction of prochiral ketones by transfer hydrogenation is catalysed by amino acid derivatives. A mechanistic suggestion for the origin of enantioselective induction has been proposed.306 ,/M Jnsaluralcd nitriles are efficiently reduced by a Cu(I)-H species in the presence of bisphosphine ligands. The active Cu(I)-H species was generated by the reaction of copper(II) acetate and polymethylhydrosilane.307... 

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