Enantioselective phase transfer

D. L. Hughes, U.-H. Dolling, K M Ryan, R F. Schoene-waldt, E. I. J. Grabowski, A Kinetic and Mechanistic Study of the Enantioselective Phase-Transfer Methyla-tion of 6,7-Dichloro-5-methoxy-2-phenyl-l-indanone , J. Org. Chem. 1987, 52, 4745-4752... 

E. J. Corey, Y. Bo, J. Busch-Peterson, Highly Enantioselective Phase Transfer Catalyzed Alkylation of a 3-Oxygenated Propionic Ester Equivalent Application and Mechanism , J. Am Chem Soc 1998, 120, 13000-13001. 

J. J. Eddine, M. Cherqaoui, Chiral Quaternary Benzo-phenone Hydrazonium Salt Derivatives Efficient Chiral Catalysts for the Enantioselective Phase-Transfer Alkylation of Imines. Application to Synthesis of Chiral Primary Amines , Tetrahedron Asymmetry 1995, 6, 1225-1228. 

P. Bako, T. Novak, K. Ludanyi, B. Pete, L. Toke, G. Kegle-vich, D-Glucose-based Azacrown Ethers with a Phos-phonoalkyl Side Chain Application as Enantioselective Phase Transfer Catalysis , Tetrahedron Asymmetry 1999,10, 2373-2380. 

Ye, J., Wang, Y, Liu, R., Zhang, G., Zhang, Q., Chen, J. and Liang, X. A Highly Enantioselective Phase-transfer Catalyzed Epoxidation of Enones with a mild Oxidant, Trichloroisocyanuric acid. Chem. Commun. 2003, 2714-2715. 

Reactions accomplished by enantioselective phase-transfer catalysis are summarized in Table 10.1 according to type of catalyst and synthetic transformation [9-81], Highest reported enantioselectivities (% ee) or optical purities (% op) are listed to give perspective to the overall field [82]. General aspects of phase-transfer systems, including catalysts are then discussed, followed by particular reaction classes. 

Having optimized the catalytic enantioselective phase-transfer alkylation system, the group explored the scope and limitations. A variety of electrophiles were reacted with the benzophenone imine glycine tert-butyl ester 1 catalyzed by 5 mol% of the selected chiral dimeric PTCs, benzene-linked-l,3-dimeric PTC 37, 2 -F-benzene-linked-1,3-dimeric PTC 41, and naphthalene-linked-2,7-dimeric PTC 39, at reaction temperatures of 0°C or — 20 °C (Scheme 4.8). 

Table 5.2 Catalytic enantioselective phase-transfer alkylation of glycine derivative 2 catalyzed by (S)-16Aa, (S)-16Ab, (S)-16Ba, and (S)-16Bb.

Table 5.3 Catalytic enantioselective phase-transfer alkylation of glycine derivative 2.

Bako later prepared mannose-derived crown ethers 3 in which the macrocyde and six-membered ring are cis-fused [12]. Crown ethers 3 were also found to be highly enantioselective phase-transfer catalysts, and compound 3a catalyzed the asymmetric synthesis of compound 5a in 37% yield and with 92% ee in favor of the (S)-enantiomer. In contrast, crown ethers 4 - which lack a fused ring junction -were found to be relatively poor asymmetric phase-transfer catalysts for the reaction shown in Scheme 8.3. The best results in this case were also obtained with the N-unsubstituted compound 4a, which gave compound 5a in 38% yield and with just 67% ee [13]. 

Bako. P. Novak. T. Ludanyi. K. Pete. B. Toke. L. Keglevich, G. D-glucose-based aza-crown ethers with a phosphonoalkyl side chain Application as enantioselective phase transfer catalysts. Tetrahedron Asymmetry 1999. 10. 2373-2380. 

Scheme 5.2 The first reported enantioselective phase-transfer catalyzed reaction.

Scheme 1.36 Enantioselective phase-transfer-catalyzed intramolecular aza-Michael Reaction...

Scheme 2.86 Enantioselective phase-transfer catalytic Michael addition of p-ketoesters to enones...

The enantioselective phase-transfer catalyzed Michael addition of A-(diphenyl-methylene)glycine fert-butyl ester to several Michael acceptors such as methyl acrylate, cyclohex-2-enone and ethyl vinyl ketone was initially studied by Corey et al. employing 0(9)-aUyl-Af-9-anlhraceny]melhylcinchonidimum bromide (173) (Fig. 2.24) as catalyst and cesium hydroxide as base [272]. Different studies followed this pioneering woik, presenting diverse modifications over the standard procedure such as the employment of non-ionic bases [273], variations of the nucleophile functionality [274], and using new chiral phase-transfer catalysts, the most attention paid to this latter feature. For instance, catalyst 173 was successfully employed in the enantioselective synthesis of any of the isotopomers of different natural and unnatural amino acids... 

Enantioselective phase-transfer catalysis (PTC) has been extensively applied for the alkylation, epoxidation, conjugate addition and related process, with the use of chiral ammonium salts being the typical transfer agent [293]. However, the related aldol... 

Scheme 16.10 Enantioselective phase-transfer catalytic diallq lation using polymer-supported glycine imine esters 15 and 17.

The asymmetric induction originates on the steric screening of the complexed nucleophile anion provided by the chiral tetrahedral ammonium cation [193], From this point of view, enantioselective phase-transfer catalysis can be regarded as a particular case of asymmetric countercation-directed catalysis. In 2008, Ooi... 

Enantioselective phase-transfer catalysis has also been successfiilly applied to intramolecular aza-Michael reactions, as elegantly exemplified by Bandini and Umani-Ronchi in the reaction of amide tethered indolyl a,p-unsaturated esters to yield 3,4-dihydropyrazino[l,2-a]-indol-l(2/i)-ones [109]. With the general assumption that the annulation reaction proceeds to give products with (5) configuration, a proposal for the transition state of the enantioselective step of the reaction was made by the same group two years later [110]. In this transition step a favorable ir-stacking interaction between the indole and the benzyl-CF3 groups was postulated (Scheme 11.30). 

Enantioselective Phase-Transfer Catalyzed Reactions. TAA salts are readily available as single enantiomers via quaternization of trialkylamines containing chiral substituents, most often alkaloids. One could therefore expect that use of chiral TAA salts as PT catalysts would result in enantiodifferentia-tion in reactions of prochiral educts, thus affording asymmetric synthesis. A priori... 

Scheme 3.17 Enantioselective phase-transfer alkylation catalyzed by 20.

Scheme 2.18 Enantioselective phase-transfer catalysis synthesis of pyrazolines.

Mahe, O., Dez, L, Levacher, V., Briere, J.-F. (2010). Enantioselective phase-transfer catalysis synthesis of pyrazoUnes. Angewandte Chemie International Edition, 49,7072-7075. 

In seeking to realise this notion, we chose carboxylates as substrates for two reasons. Firstly, we could avail of the well-known carboxylate-guanidinium recognition motif, as in 11, to establish and dominate complex formation.Secondly, the amphiphilic nature of carboxylates allowed us to aim for enantioselective phase transfer, an easy phenomenon to detect and potentially very useful for the large scale resolution of racemates. ... 

Hughes DL, Dolling UH, Ryan KM, Schoenewaldt EE, Grabowski, EJJ. Efficient catalytic asymmetric alkylations. 3. A kinetic and mechanistic study of the enantioselective phase-transfer methylation of 6, 7-dichloro-5-methoxy-2-phenyl-l-indanone. J. Org. Chem. 1987 52(21) 4745 752. 

Ooi T, Takeuchi M, Kato D, Uematsu Y, Tayama E, Sakai D, Maruoka K. Highly enantioselective phase-transfer-catalyzed alkylation of protected a-amino acid amides toward practical asymmetric synthesis of vicinal diamines, a-amino ketones, and a-amino alcohols. J. Am. Chem. Soc. 2005 127(14) 5073-5083. 

Kim M, Park Y, Jeong B, Park H, Jew S. Synthesis of ( )-paroxetine via enantioselective phase-transfer catalytic monoalkylation of malonamide ester. Org. Lett. 2010 12 (12) 2826-2829. 

Some phase-transfer catalytic asymmetric alkylation reactions of glycine imine derivatives have been explored to access natural products and biologically active compounds. For example, by employing an enantioselective phase-transfer catalytic alkylation, Kim et al. accomplished the first asymmetric total synthesis of the naturally occurring phenanthroindolizidine alkaloid (—)-antofine (Scheme 12.2) [102]. The key feature of this synthesis is the creation of the stereogenic center by reacting 65a with electrophile 66 in the presence of the dimeric catalyst 28 under the phase-transfer conditions. 

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