BINAP rhodium catalyst

Nitroalkenes are good candidates for the rhodium-catalyzed asymmetric 1,4-addition of organoboronic acids. Hayashi et al. reported that the reaction of 1-nitrocyclohexene with phenylboronic acid in the presence of rhodium/ -BINAP catalyst gave 99% ee of 2-phenyl-1-nitrocyclohexane (Scheme 38).117... 

The first example of an enantioselective [5 + 2]-cycloaddition was reported for the tethered alkene-VCP 7a, which upon treatment with a chiral rhodium complex afforded the m-fused bicyclo[5.3.0]decene 8a in 80% yield and 63% enantiomeric excess (ee) (Equation (6)).39 A later study found that when a 2,2-bis(diphenyl-phosphanyl)-l,l-binaphthyl (BINAP)-modified rhodium(l) catalyst is used, good to excellent ee s and yields are achieved with a variety of substrates (Equation (7)).40... 

Asymmetric cyclization was also successful in the rhodium-catalyzed hydrosilylation of silyl ethers 81 derived from allyl alcohols. High enantioselectivity (up to 97% ee) was observed in the reaction of silyl ethers containing a bulky group on the silicon atom in the presence of a rhodium-BINAP catalyst (Scheme 23).78 The cyclization products 82 were readily converted into 1,3-diols 83 by the oxidation. During studies on this asymmetric hydrosilylation, silylrhodation pathway in the catalytic cycle was demonstrated by a deuterium-labeling experiment.79... 

Under a pressure (20 bar) of carbon monoxide, carbonylative silylcarbocyclization of enyne 92 was examined in the presence of a cationic rhodium-BINAP catalyst (Scheme 31).86 Although the enantioselectivity is low, the five-membered carbocycle functionalized with an alkenylsilane moiety and a formyl group was obtained with high selectivity. 

Striking examples of this phenomenon are presented for allyl and homoallyl alcohols in Eqs. (5) to (7). The stereodirection in Eq. (5) is improved by a chiral (+)-binap catalyst and decreased by using the antipodal catalyst [60]. In contrast, in Eq. (6) both antipode catalysts induced almost the same stereodirection, indicating that the effect of catalyst-control is negligible when compared with the directivity exerted by the substrate [59]. In Eq. (7), the sense of asymmetric induction was in-versed by using the antipode catalysts, where the directivity by chiral catalyst overrides the directivity of substrate [52]. In the case of chiral dehydroamino acids, where both double bond and amide coordinate to the metal, the effect of the stereogenic center of the substrate is negligibly small and diastereoface discrimination is unsuccessful with an achiral rhodium catalyst (see Table 21.1, entries 9 and 10) [9]. 

Industrial practice. Both the ligand, S-BINAP, and rhodium are rather expensive (both = 50-150 per gram) and the turnover per mole of catalyst... 

As another way of constructing nitrogen-containing heterocycles enantioselec-tively, the use of 3-aIkoxycarbonyl-3-pyrrolines as substrates has also been described in the rhodium-catalyzed asymmetric 1,4-addition reactions (Figure 3.41). Among the conditions examined, it was found that [Rh(OH)(cod)]2/(5)-binap catalyst is uniquely effective for achieving high yield of the 1,4-adducts. 

Asymmetric 1,4-addition of arylzinc chlorides to ( >3-arylpropenals has proceeded with high enantioselectivity in the presence of a rhodium-(/ )-binap catalyst and chlorotrimethylsilane.102 The corresponding 3,3-diarylpropanals were obtained in high yields and excellent enantiomeric excess (98-99% ee). 

The bisphosphine ligand Biphemp (106a) has been used in rhodium catalysts in the asymmetric isomerization of N,/V-diethyIneryTamine with enantioselectivities up to 99.5% ee. [Rh(Biphemp)]+ catalysts compared favorably to [Rh(BINAP)]+ catalysts in rate and enantioselectivities.120... 

One additional favourable feature of the use of rhodium-BINAP catalysts is that they are stereospecific the ( )-enamine gives the (i )-amine and the Z)-enamine gives the (5)-amine with catalysts containing (5)-BINAP. Obviously, the use of (i )-BINAP catalysts affords the opposite enantiomers of the amine (Figure 21). Thus to obtain a high enantiomeric purity, it is essential to start from isomerically pure amine. Almost perfect enantioselectivity (> 96% ee) and quantitative yields were obtained by all routes. Initially, [Rh(BINAP)(-COD)]" (COD = 1,5-cyclooctadiene) was used as catalyst precursor, and TON up to 8000 were achieved. Further improvements in TON were achieved with... 

For the transfer of arj l and alkenyl groups to enones, Hayashi s procedure, employing the corresponding boronic adds and a rhodium-BINAP catalyst, is the method of choice at present [24, 25]. For the transfer of alkyl groups to cydic enones the use of dialkylzinc reagents in the presence of copper-phosphoramidite catalysts is superior. Although the first examples of hi ly enantiosdective 1,4-ad-ditions of R Zn reagents to nitroalkenes have been reported, similar catalytic methods for numerous other dasses of a, -unsaturated compounds still need to be devdoped. 

Keywords Allylamine, BINAP, Catalyst recycle, Citronellal, Enamine, Ene reaction. Isomerization, Menthol, Rhodium complex, Telomerization, Terpenoids... 

A small number of enantiomerically pure Lewis acid catalysts have been investigated in an effort to develop a catalytic asymmetric process. Initial work in this area was carried out by Narasaka and coworkers using the titanium complex derived from diol (8.216) in the cycloaddition of electron-deficient oxazolidinones such as (8.217) with ketene dithioacetal (8.218), alkenyl sulfides and alkynyl sulfides. Cyclic alkenes can be used in this reaction and up to 73% ee has been obtained in the [2- -2] cycloaddition ofthioacetylene (8.220) and derivatives with2-methoxycarbonyl-2-cyclopenten-l-one (8.221) usingthe copper catalyst generated with bis-pyridine (8.222). Furthermore, up to 99% ee has been obtained in the [2-1-2] cycloaddition of norbornene with alkynyl esters using rhodium/Hs-BINAP catalysts. This reaction is not restricted to the use of transition metal-based Lewis... 

In the next step, diethylgeranylamine is treated with an enantiomericaUy pure rhodium-BINAP catalyst. The product, an enamine of citroneUal, is obtained in quantitative yield and in high optical purity. 

Among the vast number of chiral homogeneous catalysts, rhodium(I) and ruthenium(II) diphosphane complexes revealed to be the most efficient ones in asymmetric hydrogenation of functionalized olefins of practical importance. In certain cases described below (including also the BINAP-containing systems), enzyme-like enantioselectivities matching the requirements of natural product synthesis were reported. 

The intramolecular [2+2+2] cycloaddition of triynes affords tricyclic compounds, which are not readily accessible by other methods. The double [2+2+2] cycloaddition of a diphenylphosphinoyl-substituted hexayne proceeded in the presence of the cationic rhodium(I)/tol-BINAP catalyst to give the corresponding Cj-symmetric axially chiral biaryl bisphosphine oxide with high enantioselectivity (Scheme 21.24) [28]. 

Aryl ethynyl ethers can also be employed in cationic rhodium(I) complex-catalyzed intermolecular [2- -2-1-2] cycloaddition. The [2- -2-1-2] cycloaddition of aryl ethynyl ethers proceeded by using the cationic rhodium(I)/Hg-BINAP catalyst (Scheme 4.13) [24], The same rhodium(I) complex catalyzed cross-[2 - - 2 - - 2] cycloaddition of two molecules of aryl ethynyl ethers with electron-deficient internal alkynes (Scheme 4.14) [24]. 

The cross-[2 + 2 + 2] cycloaddition-aromatization sequence of terminal alkynes, dialkyl acetylenedicarboxylates, and enol esters was accomplished by using a cationic rhodium(I)/BINAP catalyst (Scheme 4.15) [25]. In this reaction, commercially available and cheap liquid enol acetates could be used as gaseous acetylene and propyne equivalents, which are difficult to handle using conventional laboratory equipment, due to their explosive and flammable nature. 

The bulky phosphine ligands were synthesized via [2 + 2 + 2] cycloaddition of diynes with 1-alkynylphosphine sulfides using the cationic rhodium(I)/BINAP catalyst followed by desulfurization (Scheme 4.44) [47]. 

Use of the rhodium(I)-catalyzed double [2- -2-1-2] cycloaddition approach to the synthesis of symmetric biaryl diphosphorus compounds was first reported by Doherty et al. The reactions of l,4-bis(diphenylphosphinoyl)buta-l,3-diyne 81 with terminal a,co-diynes 80 proceeded at room temperature in the presence of the cationic rhodium(I)/BINAP catalyst to give symmetric biaryl bisphosphine oxides 82 in excellent yields (Scheme 9.29) [27]. Subsequent reduction of bisphosphine oxide 82 furnished the corresponding bisphosphine 83 (Scheme 9.29) [27]. 

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