BINOL-derived ligands

The majority of the reported phosphoramidite ligands consist of BINOL and a diversity of readily available amines. Excellent enantioselectivities in the hydrogenation of a- and /fdehydroamirio acids, itaconates and enamides [63, 64] have been reported. In a recent full report, the group of Minnaard, De Vries and Fer-inga noted that especially the BINOL-derived ligands containing a piperidine or... 

Yields and selectivities of BINOL-derived ligands in additions of Et2Zn and Me2Zn to 2-cyclohexenone are compiled in Tab. 7.2. 

Scheme 19.7 Asymmetric cyanosilylation of aldehydes catalysed by aluminium complexes of BINOL-derived ligands.

The complex of Se(OTf)3 with new BINOL-derived ligands, bearing chiral bis-oxazoline at the 3,3 -carbons (BINOL-Box), was found to catalyze the 1,3-dipolar cycloaddition of N-benzylidenebenzylamine N-oxide to 3-((E)-2-butenoyl)-l,3-oxazolidin-2-one [139]. Using 6mol% of the most effective ligand and 5mol% of the Lewis acid, the corresponding endo-isoxazolidine was obtained as the major diastereoisomer with an endojexo ratio of 97/3, and the enantioselectivity of the endo product was 87%. 

The following order of initiation rate constants was found by Grubbs et al. for 71a and some precatalysts containing one phosphine ligand 56d< 56k 71a<56h (cf. Scheme 15 for structures of 56d,h,k) [48b, 55]. Thus, 71a shows a rate of initiation comparable to that of 56k but three orders of magnitude higher than that of 56d. Nevertheless, 56d appears to be more reactive in RCM reactions than 71a [56]. Wakamatsu and Blechert were the first to report that the activity of precatalysts related to 71a can be dramatically enhanced by modification of the benzylidene unit [56]. For example, RCM of 75 using 1 mol% of BINOL-derived complex 71b yields the azacyclic product 76 in quantitative yield within 20 min (Eq. 10), whereas with 56d only 4% of 76 was obtained under these conditions [56]. 

The stereoselective synthesis of hexacoordinated phosphate anions was also reported by the same group. A general one-pot process was developed for the preparation of C2-symmetric anions 15,16 and 17 containing enantiopure BINOL, hydrobenzoin, and tartrate-derived ligands respectively [38-40] Cpsymmetric anion 18 being prepared similarly in two steps from methyl-a-... 

On the other hand, Bolm et al. have reported, more recently, the use of BINOL-derived A -phosphino sulfoximines as ligands in the rhodium-catalysed hydrogenation of dimethyl itaconate and a-acetamidoacrylates, achieving excellent enantioselectivities of up to 99% ee (Scheme 8.12). In the main... 

Scheme 8.12 Hydrogenations of olefins with BINOL-derived A -phosphino sulfox-imine ligands.

Scheme 9.21 Rh- and Ru-catalysed reductions of acetophenone with BINOL-derived S/P ligands.

On the other hand, S/0 ligands have been developed to a much lesser extent, although the high efficiency of BINOL-derived hydroxysulfoxides was demonstrated by Shibasaki s group in 2004 for the Reissert reaction. 

The asymmetric hydrogenation of quinoline continues to be of interest. Li et al. reported the asymmetric hydrogenation of a variety of 2-substituted-quinolines to the corresponding tetrahydroquinolines using an Ir-catalyst with a BINOL-derived diphosphonite ligand... 

Woodward and co-workers utilized [Gu(MeCN)4]BF4 and (A)-BINOL-derived thiourethane ligand 87 in the addition reaction of trimethylaluminum to acyclic enones. Both yields and enantioselectivities were moderate (Scheme 44).130... 

In a comprehensive screen of the effect of TADDOL and BINOL-derived phosphites on the conjugate addition of diethylzinc to representative enones, Al-exakis et al. (181) revealed that the Feringa ligand exhibits the broadest scope, providing the conjugate adducts in selectivities ranging from 66 to 92% ee, Eq. 144. 

Binol-derived phosphoroamidite PipPhos (19) has been successfully used as a ligand for the Ir-catalyzed asymmetric hydrogenation of 2- and 2,6-substituted quinolines [39], 2- and 2,6-substituted quinoxalines [40], and IV-aryl imines [41] (Fig. 16). 

Fig. 16 Summary of the best results obtained in the Ir-catalyzed hydrogenation of quinolines, quinoxalines, and Af-aryl imines using binol-derived phosphoroamidite PipPhos 19 ligand...

Reetz et al. [53] prepared analogues of (R)-binol as ligands for the titanium complex in the presence of water under the same conditions as Uemura s mentioned above. In this study, (R)-octahydrobinol and its dinitro derivative were synthesized. The reaction using (R)-dinitro-octahydrobinol ligand gave (. S j-methyl p-tolyl sulfoxide (86% ee) [53], which makes a sharp contrast to the reaction using (R)-binol wherein (A1 (-methyl p-tolyl sulfoxide was formed [50]. It is probable that kinetic resolution is involved, giving some asymmetric amplification. 

BINOL-derived phosphoramidites are versatile ligands in palladium-catalysed umpol-ung allylation of aryl aldehydes mediated by diethylzinc.172 The possible roles of allyl-zinc and -palladium species in the mechanism are discussed in detail. 

---