Ring opening of meso epoxides

The analogous chromium complex was used in the asymmetric ring opening of meso epoxides with trimethylsilyl azide [15] (Scheme 4). In this case a strong dependence on the anion of the ionic hquid was observed. Anions leading to hydrophobic ionic hquids, such as PFe" and SbFe", led to high... 

Method B was also used in the preparation of occluded (salen)Cr complexes. ligands Ih and li were prepared within the pores of Cr -exchanged EMT and Y zeolites, respectively [25]. These complexes were tested as catalysts in the ring opening of meso-epoxides with trimethylsilyl azide (Scheme 4). The occluded complexes showed a dramatic decrease in catalytic... 

Using the catalytic system described above, the enantioselective opening of meso epoxides could also be pursued. Although many excellent examples of ring-opening of meso epoxides by Sn2 reactions have recently been reported, the reaction planned here is conceptually different [40]. In the SN2 reaction, the path of the incoming nucleophile has to be controlled. In the titanocene-catalyzed reaction, the intermediate radical has to be formed selectively. If an intermediate similar to that invoked in the Bartmann ring-open-... 

Schaus, S. E. Larrow, J. F. Jacobsen, E. N. (1997) Practical synthesis of enantiopure cyclic 1,2-amino alcohols via catalytic asymmetric ring opening of meso-epoxides., J. 

Reymond, S. Brunei, J. M. Buono, G. (2000) New development in the enantioselective ring opening of meso-epoxides by various ion silicon sources catalyzed by an o-methoxyaryldiazaphosphonamide Lewis base., Tetrahedron Asymmetry, 11 4441-4445. 

Nakajima, M. Saito, M. Uemura, M. Hashimoto, S. (2002) Enantioselective ring opening of meso-epoxides with tetrachlorosilane catalyzed by chiral bipyridine N,N -dioxide derivatives.. Tetrahedron Lett., 43 8827-8829. 

Tokuoka, E. Kotani, S. Matsimaga, H. Ishizuka, T. Hashimoto, S. Nakajima, M. (2005) Asymmetric ring opening of meso-epoxides catalyzed by the chiral phosphine oxide BINAPO., Tetrahedron Asymmetry 16 2391-2392. 

Carree, F. Gil, R. Collin, J. (2005) Enantioselective ring opening of meso-epoxides by aromatic amines catalyzed by lanthanide iodo binaphtholates., Org. Lett., 7 1023-1026. 

Azoulay, S. Manabe, K. Kobayashi, S. (2005) Catalytic asymmetric ring opening of meso-Epoxides with Aromatic Amines in Water., Org. Lett, 14593-4595. 

Kureshy, R. 1. Singh, S. Khan, N. H. Abdi, S. H. R. Agrawal, S. Mayani, V. J. Jasra, R. V. (2006) Microwave-assisted asymmetric ring opening of meso-epoxides with aromatic amines catalyzed by a Ti-S-(—)-BlNOL complex.. Tetrahedron Lett., 47 5277- 5279. 

Gao, B. Wen, Y. Yang, Z. Huang, X. Liu, X. Feng X. (2008) Asymmetric ring opening of meso-Epoxides with aromatic amines catalyzed by a new proline-based N,N -dioxide-indium tris (triflate) complex,/t/v. Synth. Catal, 350 385- 390. 

Table 3 Bi-catalyzed asymmetric ring opening of meso-epoxide in water and organic solvents...

The enantioselective ring opening of meso-epoxides such as cyclohexene oxide, which uses benzoic acid as the nucleophile, was also investigated (see Scheme... 

Scheme 2.1.6.6 Enantioselective ring opening of meso-epoxides with benzoic acid.

Jacobsen s cobalt and chromium salen complexes 69 and 70 have proven extremely successful in the enantioselective ring opening of meso-epoxides (and kinetic resolution of racemic epoxides). Recent accounts of these most efficient and practical catalysts can be found elsewhere [71-73]. 

An inversion temperature was found for the ring opening of meso-epoxides by amines in dichloromethane.23 These reactions, which were catalysed by samarium iodobinaphthoxide, gave amino alcohols in high enantiomeric excess. The inversion temperature was thought arise because the reaction can occur with two different solvation clusters. 

Buono, Gerard (2001). On the Beneficial Effect of ortho-Methoxy Groups in the Asymmetric Ring Opening of meso Epoxides with Silicon Tetrachloride Catalyzed by Chiralortho-Methoxyphenyldiazaphosphonamide Lewis Bases. Angewandte Chemie, International Edition in English. 40 4536. 

The first attempt at enantioselective ring opening of meso-epoxides by using a chiral selenolate was reported in 1988 [90]. Enantiomerically pure seleno-binaphthyl compounds 65-67 were synthesized and applied to the asymmetric ring opening of cyclohexene oxide (Scheme 47). 

Enantioselective ring opening of meso-epoxides catalysed by an o-methoxyaryldiaza-phosphonamide Lewis base (374) has been achieved using various chloride ion silicon sources. The use of TMSCl leads to enantioselectivi-ties varying from 6 to 98% ee depending on the nature of the epoxide. ... 

Catalytic Asymmetric Ring Opening of meso-Epoxides... 

Denmark et al. have extended this study to the enantioselective ring opening of meso-epoxides with silicon tetrachloride catalyzed by chiral phosphoramide 71 (Table 11). In this case, enantiomerically enriched chlorohydrins have been synthesized in enantiomeric excesses varying from 7 to 87 depending on the structure of the considered substrate [68]. 

Similar conditions have been applied to the ring-opening of meso epoxides using amines. Bismuth triflate catalyzes the reaction of cyclohexene oxide 64 with p-bromoaniline under aqueous conditions to provide the P-aminoalcohol 65 in 84% yield. In this particular case, the water solubility of the starting materials required the use of a micellar solution of sodium dodecyl sulfate (SDS) however, more soluble amines eould be employed in water and bismuth triflate alone <04TL49>. A lanthanide variant has also been reported. Thus, treatment of 64... 

Catalysts formed from Me2Zn and binaphthol 3.7 (R = H) have been used for asymmetric ene-reactions [778]. Enantioselective ring opening of meso-epoxides by n-BuSH is catalyzed by a potassium tartrate/ZnCl2 complex [559, 778, 805]. Mukaiyama and coworkers have shown that reaction of Et2Zn with chiral sulfamides 3.15 (R = PI1CH2, r-Pr) generates Lewis acids [806] that catalyze asymmetric reactions of aldehydes with ketene acetals. 

The use of zirconium complexes derived from tartramides 3.19 in asymmetric epoxidation of homoallylic alcohols does not result in any improvement over the related to titanium analogs [808]. A zirconium complex prepared from Zr(Otert-Bu)4 and (S,S,S)-triisopropylam3ne 3.22 in the presence of water catalyzes the asymmetric ring opening of meso-epoxides by /-PiMe2SiN3 (ee 85%), while related titanium complexes are less efficient [805,831]. 

Scheme 8.11. (a) Group-selective ring-opening of meso epoxides by nucleophiles leads to enantioselective syntheses of 1,2-difunctionalized compounds, (b) Azido alcohol synthesis from epoxides and trimethylsilyl azide as catalyzed by (salen)CrCl complexes (see Scheme 8.6a for general structures of salen catalysts)... 

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