Olefin isomerization enantioselective

Enantioselective Olefin Isomerizations 430 Andrea Christiansen and Armin Borner... 

In 2011, a general and highly enantioselective olefin isomerization via bio-mimetic proton-transfer catalysis with a novel cinchona alkaloid derived catalyst QDla was reported (Scheme 3.10). ... 

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... 

Kawasaki T, Shinada M, Kamimura D, Ohzono M, Ogawa A (2006) Enantioselective Total Synthesis of (-)-Flustramines A, B and (-)-Flustramides A, B via Domino Olefination/ Isomerization/Claisen Rearrangement Sequence. Chem Commun 420... 

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. 

Spectacular enantioselection has been observed in hydrogenation (cf. Section 2.2) [3] and hydrometallation of unsaturated compounds (cf. Section 2.6) [4], olefin epoxidation (cf Section 2.4.3) [5] and dihydroxylation (cf Section 3.3.2) [6], hydrovinylation (cf Section 3.3.3) [7], hydroformylation (cf Section 2.1.1) [4a, 8], carbene reactions [9] (cf Section 3.1.10), olefin isomerization (cf Section 3.2.14) [10], olefin oligomerization (cf Section 2.3.1.1) [11], organometallic addition to aldehydes [12], allylic alkylation [13], Grignard coupling reactions [14], aldol-type reactions [15], Diels-Alder reactions [12a, 16], and ene reactions [17], among others. This chapter presents several selected examples of practical significance. 

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... 

Very recently, the enantioselective total synthesis of hexahydropyrrolo[2,3-h]-indole alkaloids, (-)-pseudophynaminol, through tandem olefination, isomerization and asymmetric Claisen rearrangement was reported [81]. Using a 3-ketodi-hydroindole derivative 107, the reaction smoothly proceeded under extremely... 

There are few examples of asymmetric catalytic processes which are of practical use. A new study on the catalytic olefin isomerization of, A-diethylneryl-amine (32) or A,JV-diethylgeranylamine (33) has now shown that optically active iV,A-diethylcitronellal-(E)-enamine (34) can be obtained with excellent enantioselectivity (> ca. 95 % e.e.) and chemoselectivity (> ca. 98 %) (Scheme 51). 

Kawasaki, T, Shinada, M., Kamimura, D., Ohzono, M., and Ogawa, A. (2006) Enantioselective total synthesis of (—)-flustramines A, B and (—)-flustramides A, B via domino olefination/isomerization/Claisen rearrangement sequence. Chem. Commun., 420-422. 

In Ghosh s enantioselective total synthesis of the cytotoxic marine macrolide (+)-amphidinolide T1 (318) [143], the C1-C10 fragment 317 was constructed by CM of subunits 315 and 316 (Scheme 62). The reaction mediated by catalyst C (5 mol%) afforded in the first cycle an inconsequential 1 1 mixture of (E/Z)-isomeric CM products 317 in 60% yield, along with the homodimers of 315 and 316. The self-coupling products were separated by chromatography and exposed to a second metathesis reaction to provide olefins 317 in additional 36% yield [144]. 

Mazet et al. have reported an efficient asymmetric isomerization reaction of allylic alcohols [60, 61]. In a preliminary report they utilized the BArp analog of Crabtree s complex to efficiently catalyze a hydride transfer from the a position of the allylic alcohol to the p position of the olefin with a concomitant formation of a formyl group. A subsequent report detailed a remarkable enantioselective variant of this process catalyzed with Ir(12g) and (12h) (Scheme 12). 

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]... 

A range of allylic alcohols are isomerized with good enantioselection by Rh(I)/PF-P(o-To1)2 (Tab. 4.1). As the steric demand of the alkyl group on the olefin increases, the enantioselectivity increases (entries 1-3). In contrast, the stereoselectivity does not appear to be particularly sensitive to either steric or electronic variations in the aryl substituent (entries 3-6). 

Olefins that lack an aromatic substituent can also be isomerized by Rh(l)/PF-P(o-To1)2 with good enantioselectivity (Eq. 8). Interestingly, for this class of substrates the reactions of E- and Z-allylic alcohols proceed with similar enantioselection. 

Stability, activity and chemo- and enantioselectivity increased with increasing steric demand of the ortho substituent R. Introduction of the trimethylsilyl group at this position (ligand 38) therefore resulted in an excellent enantioselective system which belongs among the best Pd catalysts described so far for asymmetric hydrovinylation. Almost 70% conversion was observed within 15 min. The product was obtained in 78.5% ee and only a small amount of the isomerization products was detected in the reaction mixture. However, at higher conversions, isomerization of the product to the internal achiral olefin took place. Therefore,... 

Asymmetric epoxidation of prochiral olefins is a powerful strategy for the synthesis of enantiomericaUy enriched epoxidesJ Previously, we reported a fructose-derived catalyst (1) that gives high ee for a wide variety of trans- and trisubstituted olefins (Figure 6.5). " Recently, we discovered a new catalyst (2) derived from D-glucose that can epoxidize many c -olefins with high enantioselectivity and no c w/rran -isomerization. ... 

This experimental procedure in section 6.5.7 can be used to epoxidize certain cyclic as well as acychc cw-olefins with good enantioselectivity and no cis/trans-isomerization (Table 6.7). Promising results have also been observed for some terminal olefins with this new glucose-derived catalyst, which complements our previously reported trans- and trisubstituted olefin catalyst 1. 

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