Arene oxides optically active

The publication (70) in 1976 of the preparation of optically active epoxyketones via asymmetric catalysis marked the start of an increasingly popular field of study. When chalcones were treated with 30% hydrogen peroxide under (basic) phase-transfer conditions and the benzylammonium salt of quinine was used as the phase-transfer catalyst, the epoxyketones were produced with e.e. s up to 55%. Up to that time no optically active chalcone epoxides were known, while the importance of epoxides (arene oxides) in metabolic processes had just been discovered (71). The nonasymmetric reaction itself, known as the Weitz-Scheffer reaction under homogeneous conditions, has been reviewed by Berti (70). 

In the aromatic-ring-annelated oxepin series the resonance effect is clearly the major influence dominating other factors (e.g. temperature, solvent, etc.) which affect the oxepin-arene oxide equilibrium. It is however very difficult to exclude the presence of a minor (spectroscopically undetectable) contribution from either tautomer at equilibrium. This problem has been investigated by the synthesis of chiral arene oxides from polycyclic aromatic hydrocarbons (PAHs). The presence of oxepin (26) in equilibrium with naphthalene 1,2-oxide has been excluded by the synthesis of the optically active arene oxide which showed no evidence of racemization in solution at ambient temperature via the achiral oxepin (26) <79JCS(Pl)2437>. 

Groves et al. found that a simple heme-iodosobenzene system mimics the enzymic reactions.127 Cyclohexane and cyclohexene are oxidized to cyclohexanol and a mixture of cyclohexene oxide and cyclohexenol respectively by this system. Using meso-tetrakis-a,/J,a,/J-(o-acylamidophenyl)por-phinatoiron(III) chloride where the acyl group is (i )-2-phenylpropionyl or (S)-2 -methoxy-carbonyl-l,T-binaphthyl-2-carbonyl, optically active styrene oxides are obtained in 51% e.e. The Fe(TPP)Cl-PhIO system can also oxygenate arenes to arene oxides.128 Based on the following observations, mechanisms involving O—Felv(Por) t as the active species have been proposed (Scheme 30).127... 

Among the preparative methods used for obtaining P-chiral phosphorus compounds, there are procedures involving the use of optically pure auxiliaries like (—)-menthol [40], (—)-ephedrin [41,42], or more recently, the kinetic resolution of 1-hydroxymethylalkylphenylphosphine oxides using Pseudomonas or Candida antarctica lipases [43], It has been found that some [(alkyl-substituted)arene] phosphinates and phosphine oxides can also be resolved efficiently by inclusion complexation with optically active 2,2 -dihydroxy-1, 1 -binaphthyl (17) [44],... 

Asymmetric synthesis of Ar(CH2) S CHCl2.1 Oxidation (NaOCl) of arene-thioacetates, Ar(CH2)nSCH2COOR, complexed with p-cycloodextrin results in optically active a,oi-dichlorosulfoxides in 4-54% ee in 70-83% chemical yield. The highest optical yield is obtained in the oxidation of C6H5SCH2COOBu. 

Optically active arene oxides. Arene oxides have been the subject of recent investigation because they are primary intermediates in the metabolism of... 

Synthesis and Reactivities of Aromatic Oxides. Certain optically active arene oxides, which are of biological significance as metabolites of polycyclic aromatic hydrocarbons (PAH), undergo spontaneous racemisation. The most plausible mechanism for this involves ring opening to the corresponding oxepins... 

In contrast to the developments in the areas of arene oxidation, a general method for the controlled epoxidation of alkenes has not been found. There have been reports that indicate that terminal alkenes can be converted into optically active epoxides, but there is nothing yet to rival the Sharpless oxidation of allylic alcohols using a chiral titanium catalyst (Scheme 4.27) as a general synthetic method. However, it should be... 

Cyclic Dienes - A number of optically active tricarbonyl iron ic-complexes with unsymmetrical cyclohexadiene and cyclohexadienyl ligands have been prepared from diols available by the oxidation of arenes by Pseudomonas putida. The circular dichroism spectra of the metal complexes were shown to provide an empirical guide for the assignment of absolute configuration from chiroptical data for this class of compounds. 

When using aliphatic aldehydes tethered to arene motifs as substrates, an enan-tioselective sequential aza-hetero-Diels-Alder and Friedel-Crafts reaction was successfully achieved by the same group [63]. Similarly, optically active lactone[3,3-b] piperidine skeletons 140 can be obtained by tandem aza-hetero-Diels-Alder reaction-hemiacetal formation-oxidation from a,P-unsaturated imines 136 and glutaraldehyde (139) (Scheme 38.41) [64]. Enamine catalysis of the inverse-electron-demand aza-hetero-Diels-Alder reaction was further extended to o-benzoquinone diimide 141 by Chen s group [65]. Various hydroquinoxalinones 142 can be obtained in high yields with excellent enantioselectivities (Scheme 38.42). 

Alcohols will serve as hydrogen donors for the reduction of ketones and imi-nium salts, but not imines. Isopropanol is frequently used, and during the process is oxidized into acetone. The reaction is reversible and the products are in equilibrium with the starting materials. To enhance formation of the product, isopropanol is used in large excess and conveniently becomes the solvent. Initially, the reaction is controlled kinetically and the selectivity is high. As the concentration of the product and acetone increase, the rate of the reverse reaction also increases, and the ratio of enantiomers comes under thermodynamic control, with the result that the optical purity of the product falls. The rhodium and iridium CATHy catalysts are more active than the ruthenium arenes not only in the forward transfer hydrogenation but also in the reverse dehydrogenation. As a consequence, the optical purity of the product can fall faster with the... 

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