Chiral epoxidation

These reagents may be considered to be one of the elusive aza-analogues of peroxyacids, and there are significant mechanistic similarities between the Rees-Atkinson reaction and the Bartlett epoxidation. Chiral Q-reagents have been used to effect highly stereoselective aziridination of alkenes (Scheme 4.13) [1],... 

Sulfur ylides are a classic reagent for the conversion of carbonyl compounds to epoxides. Chiral camphor-derived sulfur ylides have been used in the enantioselective synthesis of epoxy-amides <06JA2105>. Reaction of sulfonium salt 12 with an aldehyde and base provides the epoxide 13 in generally excellent yields. While the yield of the reaction was quite good across a variety of R groups, the enantioselectivity was variable. For example benzaldehyde provides 13 (R = Ph) in 97% ee while isobutyraldehyde provides 13 (R = i-Pr) with only 10% ee. These epoxy amides could be converted to a number of epoxide-opened... 

The MABR-promoted rearrangement, when applied to optically active epoxy substrates, has been shown to proceed with rigorous transfer of the epoxide chirality. Accordingly, used in combination with the Sharpless asymmetric epoxidation of allylic alcohols,5 this rearrangement represents a new approach to the synthesis of various... 

Kureshy, R. I. Singh, S. Khan, N. H. Abdi, S. H. R. Ahmad, I. Bhatt, A. Jasra R. V. (2005) Improved catalytic activity of homochiral dimeric cobalt salen complex in hydrolytie kinetic resolution of terminal racemic epoxides.. Chirality, 17 590-594. 

Keywords Asymmetric epoxidation Chiral iminium salt Chiral ketone... 

Like epoxides, chiral non-racemic aziridines are useful synthetic intermediates [3, 71], and a number of methodologies have been developed for their asymmetric synthesis [3, 6, 14, 72, 73]. Although several groups have developed stoichiometric methods using chiral ylides [16, 20, 22, 74, 75], catalytic asymmetric ylide azir-idinations remain relatively rare. In fact, the first catalytic aziridination with an ylide was only reported ten years ago [76]. Progress in this area is reviewed in the following section. 

Roberts SM, Bentley PA, Kroutil W, Littlechild JA (1997) Preparation of polyamino acid catalysts for use in Julia asymmetric epoxidation. Chirality 9 198-202... 

Shi asymmetric epoxidation Chiral-ketone catalyzed epoxidation of unfunctionalized olefins. 410... 

Salvador , P., Pini, D., Petri, A., Mandoli, A. Catalytic heterogeneous enantioselective dihydroxylation and epoxidation. Chiral Catalyst Immobilization and Recycling 2000, 235-259. 

Using optically active epoxides, chiral N-alkylated pyrazole and imidazole derivative ligands have been prepared by high pressure reactions with 103 or 104 their catalytic efficiency as chiral ligands in the enantioselective addition of diethylzinc to benzaldehyde has been tested. 

Hingerty, B.E., Ibanez, V., Margulis, LA., Geadntov, N.E., Broyde, S., and Patel, D.j. (1992) Influence ofbenzojo] pyrene diol epoxide chirality on solution conformations of DNA covalent adducts the (-)-trons-onti-[BP]G C... 

Bis[l,r-bi-2,2 -hydroxynaphth-3-T 2-Aryloxy alcohols. These gl From weso-epoxides, chiral products complex. Reaction with simple BI.N< due to phenolate exchange (i.e.. BLN C... 

Gross et al. reported the first use of a chiral ruthenium porphyrin Ru"(L,)(CO) as a catalyst for styrene epoxidation . Chiral ruthenium porphyrin systems have also been reported by Che et a/. . The utilization of another chiral ruthenium porphyrin, Ru"(L2)(CO) as a catalyst for enantioselective epoxidation of olefins with 2,6-dichloropyridine A-oxide has been described by Berkessel and Frauenkron ". The highest enantiomeric excesses of the oxiranes were obtained in the epoxidation of tetrahydronaphthalene and styrene, 77% and 70% ee, respectively, with high jdelds (up to 88%). Terminal aliphatic olefins and tra 5-disubstituted olefins, represented by 1-octene and rraw-stilbene, were sluggish substrates and gave low ee s. The epoxidation of tetrahydronaphthalene with iodosylbenzene catalyzed by Ru(II)(L2)(CO) produced only 52% ee... 

Groves, J.T. and K.V. Shalyaev (1998). Paramagnetic H-NMR relaxation probes of stereoselectivity in metalloporphyrin catalyzed olefin epoxidation. Chirality 10, 106-119. 

Other reactions described, with varying degrees of success, have been chiral epoxidation, chiral hydrogenation, chiral iodination, and chiral reduction of keto-groups. One of the last reactions is especially interesting in using a chiral phase-transfer catalyst. Finally, Johnson and his co-workers have reported in full the asymmetric induction in their steroid synthesis via polyene cyclization [e.g. (46) (47) with ca. 90 % optical purity]. ... 

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