Chiral diphosphines

Recent developments in chirality induced by ligands, and in efficient synthetic methods for ligands such as diphosphines, chiral diamines, amino-phosphine-phosphinites, phosphino-oxazolines and diimino-diphosphines, are available in the literature.105-107... 

Remarkable success has been achieved by Fryzuk and Bosnich (247) using the complex [Rh(5,5-chiraphos)(COD)]+, where the chiral ligand 25,55-bis(diphenylphosphino)butane, a diphosphine chiral at carbons (25), is readily synthesized from 2R,3R-butane diol. TheZ-isomers of the prochiral a-N-acylaminoacrylic acid substrates were hydrogenated at ambient conditions to / -products with very high enantiomeric excess indeed, leucine and phenylalanine derivatives were obtained in complete optical purity. Catalytic deuteration was shown to lead to pure chiral f3-carbon centers as well as a-carbon centers in the leucine and phenylal-... 

H2 cat HRhCO(PPh3>3, Rli4(C0)i2 or RhsCCOie cat diphosphine (chiral)... 

Dang, T. P., J. C. Poulin et H. B. Kagan Reduction asymetrique catalysee par des complexes de metaux de transition. III. Diphosphines chirales derivees de risopropylidene dihydroxy-2,3-bis(diphenylphosphino)-1,4-butane (DIOP). J. Organo-met. Chem. 91, 105 (1975). 

The most effective catalysts for enantioselective amino acid synthesis are coordination complexes of rhodium(I) with 1,5-cyclooctadiene (COD) and a chiral diphosphine such as (JR,jR)-l,2-bis(o-anisylphenylphosphino)ethane, the so-called DiPAMP ligand. The complex owes its chirality to the presence of the trisubstituted phosphorus atoms (Section 9.12). 

The disclosure, in 1982, that cationic, enantiopure BINAP-Rh(i) complexes can induce highly enantioselective isomerizations of allylic amines in THF or acetone, at or below room temperature, to afford optically active enamines in >95 % yield and >95 % ee, thus constituted a major breakthrough.67-68 This important discovery emerged from an impressive collaborative effort between chemists representing Osaka University, the Takasago Corporation, the Institute for Molecular Science at Okazaki, Japan, and Nagoya University. BINAP, 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (Scheme 7), is a fully arylated, chiral diphosphine which was introduced in... 

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-... 

Although sulfur is unHkely to chelate the metal in this case, it is worth mentioning the axially chiral diphosphine Hgands, based on hz-thienyl systems which increase the electronic density at phosphorus such as 159 (used in Ru-catalyzed reduction of /1-keto esters with 99% ee) [llla],BITIANP 160,andTMBTP 161 (in a Pd-catalyzed Heck reaction, the regio- and enantioselectivity are high with 160 but low with 161) [mb]. 

For example, the hydrogenation of methyl (Z)-a-acetamidocinnamate gives a chiral product when conducted in the presence of a chiral diphosphine catalyst. The enantiomeric excess data for micro-reactor and batch operation are in line when performed imder similar conditions [169]. A very high reproducibility of determining data on enantiomeric excess was reported [170]. In addition, the ee distribution was quite narrow 90% of aU ee data were within 40-48% [170]. 

Similar catalytic reactions allowed stereocontrol at either of the olefin carbons (Scheme 5-13, Eqs. 2 and 3). As in related catalysis with achiral diphosphine ligands (Scheme 5-7), these reactions proceeded more quickly for smaller phosphine substrates. These processes are not yet synthetically useful, since the enantiomeric excesses (ee s) were low (0-27%) and selectivity for the illustrated phosphine products ranged from 60 to 100%. However, this work demonstrated that asymmetric hydrophosphination can produce non-racemic chiral phosphines [13]. 

Almost no attention has been paid to diphosphine sulfides employed as chiral ligands for palladium-catalysed nucleophilic substitution reactions. In this context, enantiomerically pure diphosphine sulfides derived from 2,2 -biphosphole, which combined axial chirality and phosphorus chiralities, were synthesised, in 2008, by Gouygou et al. through a four-step synthetic sequence. Among various palladium catalytic systems derived from this type of ligands and evaluated for the test reaction, that depicted in Scheme 1.62... 

On the other hand, the enantioselective 1,4-addition of carbanions such as enolates to linear enones is an interesting challenge, since relatively few efficient methods exist for these transformations. The Michael reaction of p-dicarbonyl compounds with a,p-unsaturated ketones can be catalysed by a number of transition-metal compounds. The asymmetric version of this reaction has been performed using chiral diol, diamine, and diphosphine ligands. In the past few years, bidentate and polydentate thioethers have begun to be considered as chiral ligands for this reaction. As an example, Christoffers et al. have developed the synthesis of several S/O-bidentate and S/O/S-tridentate thioether... 

Another class of chiral diphosphine ligands bearing two interconnected thiophene rings, has been successfully developed by Sannicolo et al. These bis(diphenylphosphino)[Z)]thiophene ligands, called tetraMe-BITIANP and... 

Finally, Sinou et al. have shown that rhodium(I) catalysts formed with various chiral sulfonated diphosphines were efficient catalysts for the... 

Another class of chiral sulfur-containing ligands, diphosphine ligands based on a thiophene backbone, has been successfully developed by Sannicolo et For the first time, bis(diphenylphosphines) bidentate ligands incor-... 

---