BINAP olefin isomerization

Mikami and Hatano70 demonstrated the efficiency of the dicationic [Pd(MeCN)4](BF4)2/BINAP catalyst system in DMSO with the highly enantioselective synthesis of a variety of quinoline derivatives, including spiro-compound 99 (Equation (63)), resulting from olefin isomerization of the Alder-ene product. 

One of the landmark achievements in the area of enantioselective catalysis has been the development of a large-scale commercial application of the Rh(I)/BINAP-catalyzed asymmetric isomerization of allylic amines to enamines. Unfortunately, methods for the isomerization of other families of olefins have not yet reached a comparable level of sophistication. However, since the early 1990s promising catalyst systems have been described for enantioselective isomerizations of allylic alcohols and aUylic ethers. In view of the utility of catalytic asymmetric olefin isomerization reactions, I have no doubt that the coming years will witness additional exciting progress in the development of highly effective catalysts for these and related substrates. 

Benzamido-cinnamic acid, 20, 38, 353 Benzofuran polymerization, 181 Benzoin condensation, 326 Benzomorphans, 37 Benzycinchoninium bromide, 334 Benzycinchoninium chloride, 334, 338 Bifiinctional catalysts, 328 Bifiinctional ketones, enantioselectivity, 66 BINAP allylation, 194 allylic alcohols, 46 axial chirality, 18 complex catalysts, 47 cyclic substrates, 115, 117 double hydrogenation, 72 Heck reaction, 191 hydrogen incorporation, 51 hydrogen shift, 100 hydrogenation, 18, 28, 57, 309 hydrosilylation, 126 inclusion complexes, oxides, 97 ligands, 19, 105 molecular structure, 50, 115 mono- and bis-complexes, 106 NMR spectra, 105 olefin isomerization, 96... 

Olefin isomerization can be promoted by a variety of metal complexes [288—294], One of the best known examples is [Rh(P-P)][C104] (produced in situ by hydrogenation of [Rh(P-P)(cod)][C104]), which converts an (Z)-allylamine 105 to a racemic ( )-enamine 106 with high chemical selectivity and conversion rate the best phosphine ligand for this purpose is BINAP, followed by dppe and dppf [295,296). 

This isomerization is enantioselective when optically active BINAP is used and provides practical access to optically active aldehydes and alcohols such as L-menthol, which is a key fragrance chemical [297—299], The proposed mechanism involves amine, iminium, and enamine as complex intermediates [300], Extension of this olefin isomerization is realized in the isomerization of an alkyne to a conjugated diene (Scheme 1-47) [301], High chemoselectivity is achieved when Pd(OAc)2 or [Pd2(dba)3]/HOAc, in the presence of phosphine, is used as catalyst (Table 1-14). The phosphine of choice is dppb although dppf could give a similar yield. 

BINAP complexes have been used extensively in asymmetric synthesis, for example in hydrogenations,389,390 olefin isomerizations,390 arylation of olefins,391 and enantioselective allylation of aldehydes.392 Palladium or platinum complexes of (165) find important applications in enantioselective C—C bond formation,393-396 whilst iridium complexes are catalysts for the hydrogenation of nonfunctionalized tri- and tetrasubstituted olefins. 97... 

Remote olefins are maintained in BINAP-Rh(l)-catalyzed allylic amine isomerizations 1. (CH3)2CO, aq. NaOH (aldol condensatlon/dehydratlon) 2. H2, Pt/C... 

With olefins other than ethene two isomeric chlorohydrins can be obtained, one of them being chiral. When pyridine was replaced by monodentate chiral amines in [PdCl3(pyridine)], the enantioselectivities were low (8-12%) (Scheme 8.3) [14]. The mononuclear [PdCl2(L2)] complexes (L2 = sulfonated p-tolyl-BINAP) performed better providing the chird chlorohydrin in 46-76% e.e. Even better activities and... 

Isomerization is a frequent side-reaction of catalytic transformations of olefins, however, it can be a very useful synthetic method, as well. One of the best-known examples is the enantioselective allylamine enamine isomerization catalyzed by [Rh (jR)-or(S)-BINAP (COD)] which is the crucial step in the industrial synthesis of L-menthol by Takasago [42]... 

Scheme 21). Scheme 22 illustrates an example of kinetic resolution of a racemic allylic alcohol with a 1,3-hydrogen shift. When racemic 4-hydroxy-2-cyclopentenone is exposed to a cationic (/ )-BINAP-Rh complex in THF, the S enantiomer is consumed five times faster than the R isomer (32). The slow-reacting stereoisomer purified as the crystalline ferf-butyldimethylsilyl ether is an intermediate in prostaglandin synthesis (33). These isomerizations may occur via initial Rh-olefinic bond interaction (34). 

The mechanism involving simple nitrogen-coordinated complexes also accounts for reactivities of certain sterically constrained systems. For instance, 3-(diethyamino)cyclohexene undergoes facile isomerization by the action of the BINAP-Rh catalyst (Scheme 18). The atomic arrangement of the substrate is ideal for the mechanism to involve a three-centered transition state for the C—H oxidative addition to produce the cyclometalated intermediate. The high reactivity of this cyclic substrate does not permit any other mechanisms that start from Rh-allylamine chelate complexes in which both the nitrogen and olefinic bond interact with the metallic center. On the other hand, fro/tt-3-(diethylamino)-4-isopropyl-l-methylcyclohexene is inert to the catalysis, because substantial I strain develops during the transition state of the C—H oxidative addition to Rh. 

Alkenyl carboxylates and enamides are topologically analogous to each other. Both possess a carbonyl oxygen atom that is located three atoms from the olefin. The correct arrangement facilitates chelation to a metal center to realize high asymmetric induction. In fact, the BINAP-Ru complex is effective for hydrogenation of a 70 30 E/Z mixture of ethyl a-(acetoxy)-/3-(isopropyl)acrylate in 98% optical yield (Eq. 2.4) [34]. The E/Z isomeric mixtures can be employed without detrimental effect on the selectivity. 

In the study of Ru-BINAP catalyzed asymmetric hydrogenation of geraniol 10, a striking isomerization to y-geraniol 11 was observed, Eq. (5) [24]. The reaction is noteworthy in that it promotes the olefin migration from an inner to an exo position. Originally the presence of 11 was supposed to be an intermediate... 

In 1976 the first example of the asymmetric isomerization of prochiral allyl alcohols to aldehydes was reported [26]. The isomerization proceeds by migration of the olefinic double bond of allyl alcohol 12 from the 2,3 position to the 1,2 position to give enol 13, which transforms rapidly to aldehyde 14 (Scheme 2). It was claimed that DIOP (15)-modified rhodium catalysts (Fig. 1) exemplified the enantiorecognition in 2 to 4% ee. After their successful use for allylamines, BINAP (16)-coordinated rhodium catalysts (Fig. 1) were applied for the isomer-... 

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