- Diastereoselectivity in the epoxidation of substituted cyclohexenes by dimethyldioxirane
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Three series of compounds based on the cyclohexene framework have been epoxidized by dimetbyldioxirane. A pronounced dependence of epoxide diastereoselectivity on substituent has been observed. In addition there is a solvent influence on this stereoselectivity. The results have been explained by invoking steric, H-bonding, and dipole - dipole influences on the epoxide stereochemistry.
- Murray, Robert W.,Singh, Megh,Williams, Brian L.,Moncrieff, Hazel M.
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p. 1830 - 1841
(2007/10/03)
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- EANTIOSELECTIVITY OF THE MICROSOMAL EPOXIDE HYDROLASE: HYDROLYSIS OF (+/-)-CIS-3-BROMO-1,2-EPOXYCYCLOHEXANE
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The acid-catalysed and the rabbit microsomal epoxide hydrolasa-catalysed hydrolysis of (+/-)-cis-3-bromo-1,2-epoxycyclohexane (1) have been investigated.Both reactions were completely regio- and stereo-specific, giving t-3-bromocyclohexane-r-1,t-2-diol (2) as the only product.Epoxide (1) was found to be a much better substrate for the epoxide hydrolase than its trans-diastereoisomer.Under enzyme saturation conditions the hydrolysis was fairly eneantioselective, as shown both by the biphasic shape of its kinetic profile and by the isolaton of optically active (-)-(1R,2R,3S)-(1) and (-)-(1R,2S,3R)-(2) at incomplete reaction.The absolute configurations have been deduced by correlation with (-)-(R,R)-trans-cyclohexane-1,2-diol.At about 30percent conversion, the enantiomeric excesses of unchanged (1) and formed (2) were 24-30percent and 56-60percent, respectively, and racemic (2) was obtained after complete hydrolysis.The results have been rationalized by a competitive inhibition of (+)-(1S,2S,3R)-(1) on the hydrolysis of (-)-(1) and fit the previously proposed picture describing the substrate enantioselection carried out by the microsomal epoxide hydrolase.
- Bellucci, Giuseppe,Ferretti, Maria,Lippi, Annalisa,Marioni, Franco
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p. 2715 - 2720
(2007/10/02)
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- Syn Bromination of 2-Cyclohexen-1-ol Benzoates. Isolation of a trans-3-Bromocyclohexano-cis-1,2-(2'-anisyl-1',3'-dioxolan-2'-ylium) Intermediate
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The addition of molecular bromine to 2-cyclohexen-1-ol benzoate, p-methylbenzoate, and p-methoxybenzoate in aprotic solvents of low to moderate dielectric constant gave, besides the expected vicinal trans diaxial and diequatorial dibromides, large amounts
- Bellucci, Giuseppe,Bianchini, Roberto,Vecchiani, Sandra
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p. 3355 - 3362
(2007/10/02)
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