Tol-BINAP complexes

H. Yamamoto reported an enantioselective allylation of aldehydes catalyzed by AgF-p-tol-BINAP complex, [Eq. (13.24)]. High enantioselectivity was obtained... 

Unsaturated esters like 198 react with Grignard reagents under similar conditions, giving excellent yields and enantioselectivities. The catalyst is a Cu -Tol-BINAP complex... 

Kinetic resolution using the AHR was achieved for the first time by Shibasaki et al. [123], The AHR of racemic 133 catalyzed by the Pd-(R)-tol-BINAP complex provided the desired product 134p, a potential synthetic intermediate for (+)-wortmannin,in 20% yield (134P 134a=l 1 1) and 96% ee (Scheme 6). 

Sodeoka et al. have developed novel chiral diaqua Pd(II)-BINAP and -Tol-BINAP complexes 67 as efficient asymmetric catalysts of the aldol reaction of SEE (Scheme 10.57) [157]. These complexes are readily prepared from PdCl2(BINAP) and PdCl2(Tol-BINAP) by treatment of 2 equiv. AgBE4 in wet acetone, and are quite stable to air and moisture. The results of H NMR experiments indicate that reaction of 67b with acetophenone TMS enolate forms an O-bound Pd enolate. 

The Tol-BINAP complexes of CuFa, CuF, and CuOt-Bu also work as efficient chiral catalysts of the aldol reactions of aromatic and a, -unsaturated aldehydes wifh dienolate 64 (Scheme 10.62) [164]. IR spectroscopy has revealed fhat the stoichiometric reaction of 64 wifh Cu(Ot-Bu)(S)-Tol-BINAP forms a Cu(I) enolate, and fhat subsequent reaction wifh an aldehyde gives a copper aldolate. The copper enolate is also obtained by stepwise treatment of 64 with Bu4NPh3SiF2 and Cu(C1O4)(S)-To1-BINAP. These results, with the known reduction of Cu(II) to Cu(I) by SEE, indicate that fhe Cu-catalyzed aldol reactions proceed fhrough a transmetalation mechanism involving a chiral Cu(I) enolate. 

Lectka et al. have reported that Tol-BI NAP-coordinated CUCIO4 catalyzes fhe addition of SEE to a-N-tosylimino esters wifh high enantioselectivity (Scheme 10.81) [227]. The use of a-substituted SEE gives anti adducts wifh high diastereoselectivity. The Tol-BINAP complex is superior to fhe corresponding BINAP complex in diastereo- and enantioselectivity. It has been proposed that this asymmetric Mannich-type reaction proceeds by a Lewis acid-catalyzed mechanism, not a transmetalation mechanism as reported by Sodeoka et al. 

In our asymmetric process development, the discovery of the thermally stable rhodium bis-BINAP complex was outstanding as it enabled the repeated use of catalyst [10]. In Scheme 3, the synthesis of the cationic rhodium bis-Tol-BINAP complex 13 is illustrated. Its precursor 12 can be prepared quantitatively using cheap sodium perchlorate in a binary system in the presence of a phase transfer catalyst. It is possible to convert 12 to 13 by monitoring the reaction either by the volume of hydrogen absorbed or the color change from orange (12) to deep red (13). 

The enantioselective completely intramolecular [2 + 2 + 2] cycloaddition also furnishes Cz-symmetric axially chiral biaryls. Shibata et al. reported the cationic rhodium(I)/tol-BINAP complex-catalyzed enantioselective [2 + 2 + 2] cycloaddition of symmetric hexaynes 58 to give Cz-symmetric axially chiral biaryls 59 with good yields and ee values (Scheme 9.21) [21]. This is the first example of an axially chiral bis(biphenylene) skeleton. 

Asymmetric a-arylations of ketones to form products containing quartemary benzyhc stereogenic centers with high enantioselectivities were also reported by Hartwig et al. and Buchwald et al. Initial studies employed the traditional Pd/BINAP or Tol-BINAP complexes, which in many cases resulted in modest enantioselectivity. Later, other combinations of Pd or Ni precatalysts with ligands such as electron-rich monodentate or bidentate phosphines, l,l -bis-substi-tuted ferrocenyl phosphines, or A(-heterocyclic carbenes/-phosphines expanded the scope of this reaction. 

The phosphine (127)-catalysed asymmetric 4 +1-cycloaddition reaction of Morita-Baylis-Hillman carbonates with dicyano-2-methylenebut-3-enoates formed highly functionalized cyclopentenes in high yields and excellent ee% The [RuCl(CO)2]2-catalysed 4 + 1-cycloaddition reaction of alkenyl propargyl acetates, RCH(OAc)C=CC(Me)=CH2, with CO in CH2CI2 produced highly functionalized cyclopentenones in high yields (96%). The chiral copper/Tol-BINAP complex... 

The complex -Tol-BINAP-AgF (/>-Tol-BINAP - 2,2 -bis(di-/)-tolylphosphanyl)-l,l -binapthyl) catalyzes the asymmetric addition of allylic trimethoxysilanes to aldehydes (Equation (7)).7 3 The process can provide various optically active homoallylic alcohols with high enantioselectivity (up to 96% ee) and a remarkable 7 and anti- selectivities are observed for the reaction with crotylsilanes, irrespective of the configuration of the double bond ... 

This reaction has lent itself to the development of its asymmetric version (Scheme 88). The trick here is to remove the choride ligands from the coordination sphere of the platinum-chiral ligand complex. This makes the metal center more electrophilic, thus reactive reactions can be run at lower temperature. Interestingly, the best ligand was found to be the atropisomeric monophosphine (fJ)-Ph-BINEPINE.312 Enantiomeric excess up to 85% was observed. Very recently, enantioselectivity up to 94% ee has been achieved using [(AuCl)2(Tol-BINAP)] as pre-catalyst for the reaction of another enyne.313... 

Catalytic enantioselective dienolate additions to aldehydes were realized by Tol-BINAP-Cu(ll) fluoride complexes as shown by an example in Equation (131). 

More recent work employing diphosphine ligands has focused on both new substrates for hydroboration and also new hydroborating agents. Specifically, Gevorgyan has successfully employed cyclopropenes 56 as substrates, with pinacolboranes 13 as the borane source.20 Impressive enantioselectivities were obtained with a range of diphosphines, for example, with rhodium complexes of NORPHOS (>99% ee), PHANEPHOS (97% ee), BINAP (94% ee), and Tol-BINAP (96% ee), all with near perfect m-selectivity (see Scheme 8). 

Noyori et al. recently used ESI-MS to characterize species present in catalytically active solutions during the hydrogenation of aryl-alkyl ketones using their base-free catalyst precursors trans-[Ru((R)-tol-BINAP)((R, RJ-dpenJfHXf/ -BH ] (tol-BI-NAP = 2,2 -bis(ditolylphosphino) -1, T-binaphthyl dpen = 1,2-diphenylethylenedia-mine) in 2-propanol [9b]. Based upon ESI-MS observations, deuterium-labeling studies, kinetics, NMR observations, and other results, the authors proposed that the cationic dihydrogen complex trans-[Ru((R)-tol-BINAP)((R, R)-dpen)(H)( 2-H2)]+ is an intermediate in hydrogenations carried out in the absence of base. 

Several other chiral Lewis acids have also been reported to effect asymmetric aldol reactions. Kruger and Carreira59 reported a catalytic aldol addition of silyl dienolate to a range of aldehydes in the presence of a bisphosphanyl-Cu(II) fluoride complex generated in situ from (iS )-Tol-BINAP, Cu(OTf)2, and (Bu4N)Ph3SiF2. Aromatic, heteroaromatic, and a,/ -unsaturated aldehydes provided the aldol adducts with up to 95% ee and 98% yield (Scheme 3-33). 

Lectka and co-workers found that cationic Cu phosphine complexes are efficient Lewis acids in the activation of a-imino esters (248). The Tol-BINAP was found to be the most effective ligand providing the adduct of acetophenone enol-... 

In 1998, Carreira reported that a catalyst formed from Tol-BINAP, Cu(OTf)2, and 2 equiv of Bu4N+ Ph3SiF2 (TBAT), a soluble fluoride source, was extremely effective in mediating the aldol reaction between a silyldienolate and aromatic or vinyl aldehydes (254). Although initially formulated as a Cu(II) catalyst, subsequent evidence has shown that the active catalyst is a Cu(I) phosphine complex. By using only 2 mol% of the complex, excellent yields and enantioselectivities are observed with a range of aromatic aldehydes (93-95% ee, 86-98% yield), along with some enals (cinnamaldehyde provided the aldol adduct in 83% yield and 85% ee), Eq. 221. 

Enantioselective alkylative ring opening of these oxabicyclic alkenes has also been studied. Lautens and coworkers discovered that palladium complexes efficiently catalyze the addition of organozinc reagents to these activated alkenes with concomitant ring opening. In the presence of (Tol-BINAP)PdCl2, diethylzinc adds to oxabenzonor-... 

Addition of [1-ketoesters to unsaturated A -acylthiazolidinethiones 836 is catalyzed by the Ni(ll) Tol-BINAP Lewis acid complex 837. The initial addition products 838 cyclize upon treatment with base to afford enantiopure 3,4-dihydropyran-2-ones 839 in excellent yield (Scheme 236, Table 35) <2005JA10816>. 

The decrease in the dihedral angle of the biaryl backbone had a profound effect on both reactivity and enantioselectivity. It was determined that the catalyst [NH2Me2]+ (RuCl(/ -ScgPIIOS) 2(Li-Cl)3] can hydrogenate 2-oxo-l-propanol to (2R)- 1,2-propanediol in 98.5% ee and with an S/C ratio of 10,000. (2R)- 1,2-propanediol is used in the production of Levofloxacin (see Section 12.2.2.5). The current catalyst used in production is a R-Tol-BINAP-Ru(II) complex.130... 

Attempts to develop enantioselective protocols for the aza-Diels-Alder reaction were reported simultaneously with those described above. A first contribution in this area was the report by the. Mrgensen group,85 who studied the influence of salts of copper, silver, palladium, and zinc. Copper(I) perchlorate provides optimal yields and enantioselectivity, but complexes of BINAP (87) and Tol-BINAP (203) with AgSbF6, AgOTf, and AgC104 were able to catalyze the reaction, albeit with low enantioselectivity (Scheme 2.52). 

Jorgensen et al. reported that C2-symmetric bis(oxazoline)-copper(II) complex 25 also acts as chiral Lewis acid catalyst for a reaction of allylic stannane with ethyl glyoxylate [37]. Meanwhile, p-Tol-BINAP-CuCl complex 26 was shown to be a promising chiral catalyst for a catalytic enantioselective allylation of ketones with allyltrimethoxysilane under the influence of the TBAT catalyst [38]. Evans and coworkers have developed (S,S)-Ph-pybox-Sc(OTf)3 complex 27 as a new chiral Lewis acid catalyst and shown that this scandium catalyst promotes enantioselective addition reactions of allenyltrimethylsilanes to ethyl glyoxylate [39]. But, when the silicon substituents become bulkier, nonracemic dihydrofurans are predominantly obtained as products of [3+2] cycloaddition. 

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