Ring Opening Of Cyclohexene Oxide Research Articles

Enantioselective Ring Opening of meso-Epoxides by Aromatic Amines Catalyzed by Lanthanide Iodo Binaphtholates

[reaction: see text] Lanthanide iodo binaphtholates are efficient enantioselective catalysts for the ring opening of meso-epoxides by various aromatic amines. The study of the influence of temperature on the ring opening of cyclohexene oxide by o-anisidine catalyzed by the samarium complex shows an isoinversion effect with the maximum enantiomeric excess at -40 degrees C. Reactions of aniline, o-anisidine, or p-anisidine with five- or six-membered ring epoxides at this temperature allow the preparation of beta-amino alcohols with enantiomeric excesses up to 93%.

A supramolecular approach to an allosteric catalyst.

The design and synthesis of a novel, supramolecular allosteric catalyst system, assembled via the weak-link approach, is presented. The catalyst contains two structural Rh(I) centers in thioether- and phosphine-rich hemilabile pockets, and two functional Cr(III) centers bound within salen-based moieties. The catalytic properties of the supramolecular catalyst are compared to those of a Cr(III)-salen monomeric analogue in the context of the asymmetric ring opening of cyclohexene oxide by TMSN3. Allosteric control is afforded via reactions that occur at distal sites which open the macrocyclic cavity and facilitate the catalytic reaction. Kinetic data show a significant rate increase upon opening of the catalyst's flexible macrocyclic cavity and enhanced selectivity and reactivity with respect to the monomeric Cr(III)-salen analogue. The work presented represents a new approach to the construction of abiotic allosteric catalysts.

Asymmetric Ring-Opening of Cyclohexene Oxide with Mercaptan (Thiophenols) Catalyzed by Chiral Schiff Base/Ti(OPr- i ) 4 or (−)-(S)-Binaphthol/Ti(OPr- i ) 4

New chiral Schiff base ligands 1-4 were synthesized starting from (+)-camphor and (+)-1-(4-nitrophenyl)-2-amino-1,3-propanediol, and their application in asymmetric ring-opening of cyclohexene oxide using mercaptan (thiophenols) as nucleophiles was investigated. The aymmetric ring-opening of cylohexene oxide catalyzed respectively by chiral Schiff bases 1-4 /Ti(OPr- i ) 4 and ( m )-(S)-1,1'-binaphthalene-2,2'-diol 5 /Ti(OPr- i ) 4 complex afforded the corresponding chiral g -hydroxysulfides 6-10 in lower to good yield with lower to moderate ee values. Moreover, the using of ( m )-(S)-1,1'-binaphthalene-2,2'-diol as ligand led to better chiral induction effect.

The cleavage of meso-epoxides with homochiral thiols: synthesis of (+)- and (−)- trans-1-mercaptocyclohexan-2-ol

The synthesis of (+)- and (−)- trans-1-mercaptocyclohexan-2-ol is described. Ring opening of cyclohexene oxide with (−)-4-methoxybenzylnopan-3( R)-thiol 1a followed by oxidation gives two readily separable diastereomeric sulfoxides. These sulfoxides display very different thermal stability but both undergo regio-specific syn-elimination to give cyclohexan-1-ol-2-sulfenic acid that can be reacted in situ with 3,5-dimethylthiophenol to give a mixed disulfide. Reduction of these disulfides with lithium aluminium hydride gives the title compounds in enantiomerically pure form.

A Regio-and Stereoselective Synthesis of β-Amino Alcohols

The regio-and stereoselective ring opening of epoxide with aromatic amines catalyzed by samarium trichloride and the enantioselective ring opening of cyclohexene oxide with aniline catalyzed by lanthanide complexes were studied.

Phase-transfer-catalysed Ring Opening of Cyclohexene Oxide by Phenylacetonitrile Carbanion in the Presence of Lithium Salts†

Lithium cation assisted nucleophilic ring opening of cyclohexene oxide, by phenylacetonitrile carbanions, under phase-transfer conditions giving rise to a diastereoisomeric mixture of trans-γ-hydroxynitriles 7 and 8 is reported.

Chiral lewis acid catalysed asymmetric nucleophilic ring opening of cyclohexene oxide

Titanium and zirconium complexes of bispicolinic amides catalyze the ring opening of cyclohexene oxide with trimethylsilyl azide as nucleophile. The product, 1-azido-2-trimethylsilyloxycyclohexane, was obtained in up to 71% enantioselectivity when a catalyst prepared from (S,S)-N,N′-bis(2-pyridinecarboxamide)-1,2-diphenylethane and zirconium tetra-t-butoxide was employed under optimum conditions, which included the addition of a small amount of diethylamine in the catalyst preparation step. The nature of the catalyst is still unknown, but it seems probable that oligomeric metal species are involved.

Synthesis of chiral diferrocenyl dichalcogenides and their application to asymmetric nucleophilic ring opening of meso-epoxides

Four novel optically active bis[(R,S)- and (S,R)-2-(1-dimethylaminoethyl)ferrocenyl] dichalcogenides [abbreviated as (R,S)- and (S,R)-(Fc*E)2(E = S and Te)], each of which possesses two axial and two central elements of chirality, have been prepared by lithiation of commercially available chiral (1-dimethylaminoethyl)ferrocenes, followed by treatment with elemental sulfur or tellurium and air oxidation, in 42–65% isolated yields. The structure of the di-(S,R)-ferrocenyl disulfide has been fully characterized by X-ray crystallography. Ferrocenyl chalcogenide anions (Fc*E–) produced by reduction of the above (Fc*E)2 and the known (Fc*Se)2 with LiAlH4 in tetrahydrofuran are found to act as useful stereoselective nucleophiles for ring opening of meso-epoxides such as cyclohexene oxide, cyclopentene oxide, cyclooctene oxide and cis-stilbene oxide to give the corresponding ferrocenyl β-hydroxyalkyl chalcogenides in high yields with up to 71% diastereoisomeric excess (de). Although the diastereoselectivity depends on the combination of chalcogen atom and meso-epoxide, it is generally higher with E = S and Se than with E = Te. Selenoxide elimination of (S,R)-2-(1-dimethylaminoethyl)ferrocenyl 2-hydroxycyclohexyl selenide (66% de), obtained by the ring opening of cyclohexene oxide with (S,R)-(Fc*Se)2, gives (S)-cyclohex-2-enol with 60% ee. The S-configuration suggests that the ring opening, by the nucleophilic attack of the chiral ferrocenyl chalcogenide anion on the epoxide carbon, mainly occurs via the least hindered transition state considering the interactions between the epoxide, the 1-dimethylaminoethyl moiety and the ferrocene.