BIPHEP hydrogenations

Scheme 15 Iridium-catalyzed hydrogen-mediated coupling of alkyl-substituted alkynes to activated ketones and aldehydes. Conditions a ligand = BIPHEP, solvent = toluene, T = 80 °C b ligand = DPPF, solvent = toluene, T = 60 °C c ligand = BIPHEP, solvent = DCE,...

Iridium-catalyzed transfer hydrogenation of aldehyde 73 in the presence of 1,1-dimethylallene promotes tert-prenylation [64] to form the secondary neopentyl alcohol 74. In this process, isopropanol serves as the hydrogen donor, and the isolated iridium complex prepared from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and (S)-SEGPHOS is used as catalyst. Complete levels of catalyst-directed diastereoselectivity are observed. Exposure of neopentyl alcohol 74 to acetic anhydride followed by ozonolysis provides p-acetoxy aldehyde 75. Reductive coupling of aldehyde 75 with allyl acetate under transfer hydrogenation conditions results in the formation of homoallylic alcohol 76. As the stereochemistry of this addition is irrelevant, an achiral iridium complex derived from [Ir(cod)Cl]2, allyl acetate, m-nitrobenzoic acid, and BIPHEP was employed as catalyst (Scheme 5.9). 

R)-liINAP-RuBr2 can be successfully applied to the enantioselective hydrogenation of /i-kelo esters in the synthesis of (+)-(2R,3 W)-corynomycolic acid 115. ( S )-MeO-BIPHEP-RuBr2 was used in a similar manner in the synthesis of (R)-fluoxetine (116, Prozac ) and (S)-duloxetine (117).648... 

Using RuCl3/CK)-MeO-BIPHEP catalytic system, the /Uhydroxy ester, a key intermediate to vWF receptor antagonists Sulfobacin A, was produced through asymmetric hydrogenation in 96% yield and 99% ee (Scheme 8).266 The... 

BINAP system with excellent ee s. For example, 0// 0-bromoacetophenone can be converted into the corresponding chiral alcohol with 96% ee (Equation (72)). However, this type of substrate can be hydrogenated more effectively with the Ru/chiral phosphine/diamine system.279 Asymmetric hydrogenation of phenylthioketones has been realized with Ru catalysts. BINAP, MeO-BIPHEP,280 BDPP281 and Me-CnrPHOS,62c are efficient for this transformation (Table 17). 

A series of /3-keto phosphonates have been hydrogenated with the Ru-BINAP system to give various chiral /3-hydroxyl phosphonates (Equation (75)).286 An Ru-MeO-BIPHEP catalyst is also effective for this transformation.287 /3-Keto thiophosphonates can also be smoothly transformed into /3-hydroxyl thiophosphonates with high ee.287... 

Using Ir/MeO-Biphep/l2 catalyst system, a variety of substituted quinoline derivatives were hydrogenated in 95% yield and up to 96% ee. This method provided an efficient accesss to three naturally occurring alkaloids (Scheme 17).328 Ferrocene N, P ligand 108 is also effective for the asymmetric hydrogenation of quinolines with up to 92% ee.188a... 

The sense of diastereoselectivity in the dynamic kinetic resolution of 2-substi-tuted / -keto esters depends on the structure of the keto ester. The ruthenium catalyst with atropisomeric diphosphine ligands (binap, MeO-biphep, synphos, etc.) induced syn-products in high diastereomeric and enantiomeric selectivity in the dynamic kinetic resolution of / -keto esters with an a-amido or carbamate moiety (Table 21.21) [119-121, 123, 125-127]. In contrast to the above examples of a-amido-/ -keto esters, the TsOH or HC1 salt of /l-keto esters with an a-amino unit were hydrogenated with excellent cwti-selectivity using ruthenium-atropiso-... 

CHEP ligand, which was successfully applied in both Rh- and Ru-catalyzed en-antioselective hydrogenation [7]. Schmid et al. reported BIPHEMP [8] and MeO-BIPHEP [9] ligands, both of which were successfully applied in many Ru-cata-lyzed hydrogenations. Achiwa also developed several atropisomeric ligands such as BIMOP [10], FUPMOP [11], and MOC-BIMOP (Fig. 26.1) [12]. 

A PYRPHOS ligand was found to be effective for the hydrogenation of a / -aryl- or alkyl-substituted monoamido itaconate [107]. A MeO-BIPHEP-Ru catalyst was successfully applied for the enantioselective hydrogenation of an intermediate for the drug candoxatril in a mixed solvent (THF/H20) (Scheme 26.12) [108]. 

Enantioselective hydrogenation of / -keto phosphonates in the presence of an ( R)-BINAP-Ru complex under 1-4 atm H2 and at room temperature provides the (R)-yS-hydroxy phosphonates in up to 99% ee (Fig. 32.20) [69]. The sense of enantioface selection is the same as that observed in the reaction of / -keto carboxylic esters (see Fig. 32.14). A BDPP-Ru catalyst is also usable [70]. Similarly, / -keto thiophosphonates are hydrogenated with a MeO-BIPHEP-Ru catalyst with up to 94% optical yield [69 b]. 

BINAP-Ru catalysts also show high enantioselectivity in the hydrogenation of/ -keto sulfonates. Reaction of sodium yS-keto sulfonates with (R)-BINAP-Ru catalyst quantitatively gives the (R)-/1-hydroxy sulfonates in up to 97% ee (Fig. 32.21) [15]. In the same manner, hydrogenation of / -keto sulfones in the presence of an (R)-MeO-BIPHEP-Ru catalyst affords the (R)-hydroxy sulfones in >95% ee [71]. 

Figure 32.22 shows the diastereoselective hydrogenation of (R)-/ -keto sulfoxides with Meo-BIPHEP-Ru catalysts [72]. The R chiral center of the substrate matches with the S catalyst, giving the S,R alcohols in >99 1 selectivity, whereas reactions with the R catalyst affords a 6 94 to 10 90 mixture of the S,R and R,R diastereomeric alcohols. The diastereoselection is controlled mainly by the configuration of the catalyst. 

The hydrogenation of enamides and enol acetates without acid function is often more demanding, and at present is not applied widely. Besides a bench-scale application by Roche with a Ru-biphep catalyst [55], two examples are of interest a pilot process for a cyclic enol acetate by Roche [55], and a feasibility study by Bristol-Myers Squibb [56], both using Rh-DuPhos catalysts (Fig. 37.11). In the latter case, despite very good ee-values, a chiral pool route was finally chosen. Chiral Quests Rh-f-KetalPhos (see Fig. 37.9) has been shown to hydrogenate a variety of substituted aryl enamide model substrates at r.t., 1 bar, with very promising catalyst performance (ee 98-99%, TON 10000) [47]. 

The hydrogenation was carried out on 12-kg scale for Pfizer by Dow/Chirotech, using a cationic Rh-DuPhos catalyst [79] and on 250-kg scale by PPG-Sipsy with a Ru-biphep complex [80]. Both catalysts achieved very high enantioselectivities and medium activities. 

The hydrogenation of a-amino ketones was also a key step for the synthesis of three more pharma actives (Fig. 37.25). Roche [95] divulged a pilot process involving the hydrogenation/dynamic kinetic resolution of a cyclic a-amino ketone using an optimized MeO-biphep ligand. The Ru-catalyzed reaction was carried out on a 9-kg scale with excellent enantio- and diastereoselectivities, and very... 

Chan and coworkers developed a new diphosphine 9, related to MeO-BiPhep 5 (Fig. 10) [21]. [lr(p-Cl)(COD)]2/9/l2 catalytic system provided similar enantios-electivities than [lr(p-Cl)(COD)]2/5/l2 in the Ir-catalyzed hydrogenation of quinolines but higher enantioselectivitites in the reduction of 2-methyl-quinoxaline and 2,3,3-trimethylindolenine (Fig. 10). 

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