Frans-Stilbenes

N- Aminoaziridines have been converted to alkenes by reaction with a variety of oxidizing agents (70JA1784). Usually, the deamination reaction is stereospecific. The oxidation of l-amino-2,3-diphenylaziridines with manganese dioxide, however, was not stereospecific. The trans compound gives entirely frans-stilbene, whereas the cfs-aziridine forms a mixture of 85% trans- and 15% c -aikene. cw-Stilbene is not isomerized to trans under the reaction conditions, and the results are explained in terms of an azamine intermediate which can isomerize through a tautomeric equilibrium. 

Kira and coworkers25 found that in deaerated DMSO solution of frans-stilbene both the solute cation and anion are produced and the anions are eliminated by aeration. Since they found26 that the absorption spectra of the anthracene cation and anion are quite similar, they suggested25 that the absorption spectrum observed by Hayon for anthracene solution in DMSO is a superposition of the spectra of the solute cation and anion. This observation casts a serious question on the yield of solvated electrons found by Hayon23. 

Rajanikanth and Ravindranath44 have recently published a deoxygenation reaction for sulphoxides that uses metallic lithium in refluxing dimethoxyethane. Dialkyl and alkyl phenyl sulphoxides were reduced cleanly in yields around 70%, even if sterically hindered, but benzyl sulphoxides gave mixtures of products. For example, benzyl phenyl sulphoxide gave frans-stilbene (33%), benzyl phenyl sulphide (20%) and diphenyl disulphide (47%). These products can be rationalized by reaction pathways such as in equation (17) ... 

Table 9 Solvent-dependence of the stereochemistry of dibromides from frans-stilbene bromination." cis- and...

FIGURE 4.1.1.18.1 Logarithm of vapor pressure versus reciprocal temperature for frans-stilbene. 

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... 

Reaction of the TMS-nitro compound 1496 and the indole carboxaldehyde 1497 with a catalytic amount of TBAF led to the desired alcohol 1498, which, on further treatment with TFAA, followed by elimination of the corresponding trifluoroacetate with DBU, afforded the frans-stilbene 1499. Reductive cyclization of 1499 under Cadogan-Sundberg conditions afforded the bisindole 1500. Finally, condensation of 1500 with (dimethylamino)acetaldehyde diethyl acetal led to tjipanazole D (359) in 71% yield (796) (Scheme 5.255). 

Heck-type arylation reactions of organobismuth compounds were first reported by Asano et al. in 1973 [11]. This article described the stoichiometric reaction of styrene, Ph3E (E = group 15 elements) and Pd(OAc)2 (Scheme 2). Ph3Bi afforded frans-stilbene only in 7% yield. The major product was biphenyl, which was... 

The enormous amount of overactivation in photochemistry is not always required for solid-state cis-trans isomerizations. There are also some thermal E/Z isomerizations of crystalline olefins that are catalyzed by iodine. For example, crystalline czs-stilbenes 91 can be isomerized to give frans-stilbenes 92 without intervening liquid phases (Scheme 8). The isomerizations follow first-order kinetics with various rate constants for 4-MeO, two modifications of 2-MeO, 2-EtO, 2-n-PrO, and 2-i-PrO substitution. The activation energies vary from 20 to 32 kcal mol but could not be interpreted [54]. Similarly, cfs-l,2-diben-... 

The claims of exclusive formation of rac-stilbene dichloride upon gas-solid addition of chlorine to frans-stilbene (103) [71] and of meso-stilbene dibromide in the gas-solid addition of bromine to trans- or czs-stilbene [54] could not be verified. Scheme 12 shows the results of more detailed studies indicating the mesolrac ratios on the solid-state chlorination and bromination of trflns-stilbene (103) and some variations when the crystal size was changed [58, 60-61]. There is a risk of partial transient liquefaction if the chlorine is added too rapidly, due to initially heavy reaction. But even at the start with a stoichiometric amount of chlorine at 0.1 bar and 0 °C, a persistent product layer forms on the unground crystal powder of 103 that cannot be disintegrated by the ultrasound of a cleaning bath at 20 °C for 60 h (only 7% conversion with mesolrac ratio of 11 89 under these conditions) [22]. It is therefore unavoidable to mill the crystals of 103 to sizes <1 pm in order to overcome these rare diffi-... 

SYNTHESIS OF SYMMETRICAL frans-STILBENES BY A DOUBLE HECK REACTION OF (ARYLAZO)AMINES WITH VINYLTRIETHOXYSILANE frans-4,4 -DIBROMOSTILBENE... 

Ru(0)(biqn)(tmtacn)](C10 )2 and [Ru(0)(diopy)(tmtacn)](C10 )2 (biqn=C2 symmetric 1,T-biisoquinoline, diopy=(R,R)-3,3 -(l,2-dimethylethylenedioxy)-2,2 -bipyridine) aremadefrom [RuCl(L)(tmtacn)] + (L=biqn, diopy) and(NH )2[Ce(N03)J with Li(ClO ). Electronic and IR spectra were measured (v(Ru=(0) bands lie at 760 and 795 cm" respectively). The (diopy) complex is paramagnetic with 2.88 B.M. As stoich. [Ru(0)(biqn)(tmtacn)] + and [Ru(0)(diopy)(tmtacn)] VCH3CN they oxidised alkenes (styrene, cis and fran.y-P-methylstyrenes, fran -stilbene, nor-bomene, cyclohexene) to mixtures of aldehydes and epoxides. Conttary to expectation the (diopy) complex did not effect enantioselective epoxidations except with fran -stilbene, for which a moderate e.e. of 33% was observed [623]. 

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]. 

Efficient epoxidation of a variety of linear and cyclic alkenes by RuClj/aq. Na(IO )/(bpy)/CH2CyO-5°C/15 h was observed [735] 5-methyl- or 3,4,7,8-tetram-ethyl-phenanthroline can replace (bpy) [736], The active species when (bpy) is present is probably franx-Ru(0)2(bpy) 103(011)3 [567, 568], Competition between epoxidation and cleavage of fran -stilbene with bidentate ligands (pyridine, oxazo-line, oxazolidine and thiophene), containing two different nitrogen heterocycles either linked or separated by a spacer together with RuCyaq. Na(IO )/CH3Cy2°C was reported [737],... 

RuCl(dmso)(bpy)2]Cl and [RuCl(SOMePh)(bpy) ]Cl, called respectively rac-Ru-1 and A-Ru-2 by the authors, are made by microwave irradiation of cis-RuCljtbpy) with the the sulfoxide ligands. Trani-stilbene, styrene and R-styrene (R=p-MeO, a and P-methyl) were epoxidised by [RuCl(dmso)(bpy)3]Vaq. Ph(IOAc)2/CH3Cl3/40°C, while with [RuCl(SOMePh)(bpy)3]V TBHP/water-CH Cl fran -stilbene, fran -P-methylstyrene gave the (R,R) epoxides [947]. 

---