Frans-Stilbene oxide

The reaction of cis- and frans-stilbene oxides with phenylphosphonothioic dichloride in the presence of magnesium gives cis- and fra/ts-stilbene and (7).13 Phenylphosphinidene sulphide is postulated as being an intermediate. The zwitterion (8) bears a remarkable similarity to the controversial perepoxides which are thought to be intermediates in the reaction of singlet oxygen with alkenes. 

In 1998, Yang and coworkers reported a series of (7 )-carvone derived ketones (63) containing a quaternary center at and various substituents at (Fig. 22) [119]. The ees of fran -stilbene oxide varied with different para and meta substituents when 63b was used as the catalyst. The major contribution for the observed ee difference is from the n-n electronic repulsion between the Cl atom of the catalyst and the phenyl group of the substrate. The substitution at also influences the epoxidation transition state via an electrostatic interaction between the polarized C -X bond and the phenyl ring on franx-stilbene (Table 6, entries 3-7, 10-14). In 2000, Solladie-Cavallo and coworkers reported a series of fluorinated carbocyclic ketones... 

As stoich. [Ru(0)(bpy)(tmtacn)]VCH3CN it functioned as a competent (sic) epoxidant for alkenes, though the products were often contaminated with by-products (e.g. fran -stilbene gave fran -stilbene oxide and benzaldehyde cw-stilbene gave cis- and trans- epoxides). Kinetics of the epoxidation of norbomene and styrene were reported, with activation parameters measured and discussed [682]. Kinetics of its non-stereospecific, stoicheiometric epoxidation of aromatic alkenes in CH3CN were studied, and the rates compared with those of oxidations effected by other Ru(IV) 0x0 complexes with N-donors, e. g. [Ru(0)(tmeda)(tpy)] ", trans-[Ru(0)(Cl3bpy)(tpy)] " and [Ru(0)Cl(bpy)(ppz )] + [676]. 

However, enantioselectivies were dramatically increased in chloroform (apart from the anomalous reaction with cz-methylstilbene), when compared to those achieved in acetonitrile. We foimd that frans-stilbene, usually a poor substrate with our catalysts, is epoxidized with 67% ee in chloroform, whereas the corresponding reaction, performed in acetonitrile, only affords frans-stilbene oxide with 30% ee. 

Figure 10 Chiral separation of frans-stilbene oxide showing the speed and efficiency of SFC. Column 4.6 x 250 mm, 10 pm Chirapak-AD, 5 mL/min, 100 bar, 35°C, 40% MeOH in CO2.

That the elimination is syn has been established by use of deuterium labels. Deuterium was introduced stereospedfically by LiAlD4 reduction of cis- and frans-stilbene oxide. The product of the subsequent ester pyrolysis is frans-stilbene because of eclipsing effects in the transition state. Tlie syn elimination is demonstrated by retention of deuterium in the olefin from frans-stilbene oxide and its absence in the olefin from c -stilbene oxide. " ... 

Linearity, precision, and the limit of detection (LOD) of trans-stilbene oxide and other compounds were investigated [89]. The authors investigated the second factor and evaluated two types of commonly available chiral detectors for their possible use in chiral method development and screening polarimeters and CD detectors. It was shown that frans-stilbene oxide worked well across all the detectors examined, showing good linearity, precision, and low detection limits. 

A soln. of frans-stilbene, peroxy- A soln. of frans-stilbene oxide and... 

A number of heterocyclic type III systems have been investigated, primarily as ferroelectric dopants, but a number of the materials do display short (sometimes unstable) chiral nematic phases. Notable examples of systems based on three-membered ring heterocycles are probably best demonstrated by the materials containing the (2/ ,35)-2-oxirane carboxylic acid unit [112] and frans-stilbene oxides [115]. 

The chiral recognition abilities of these materials were investigated using racemic molecules, e.g., frans-stilbene oxide (Figure 4) by HPLC. Consequently, the enantiomers eluted at different retention times, indicating that racemic frans-stilbene oxides were completely separated. In addition, the chiral discrimination ability depended on both the DP of amylose and the preparation method. The chiral recognition ability increased with an increase in the DP of amylose, and the CSPs prepared by approach (II) were superior to those by approach 0) if the DPs were similar. Methods I and II differed only in the surface treatment processes. The silica surface in approach 0) has been end-capped with trimethylsilyl chloride, while that in approach 01) has been end-capped with 3,5-dimethylphenyl isocyanate. 

---