E-stilbenes

Fig. 13.11. A schematic drawing of the potential energy surfaces for the photochemical reactions of stilbene. Approximate branching ratios and quantum yields for the important processes are indicated. In this figure, the ground- and excited-state barrier heights are drawn to scale representing the best available values, as are the relative energies of the ground states of Z- and E -stilbene 4a,4b-dihydrophenanthrene (DHP). [Reproduced from R. J. Sension, S. T. Repinec, A. Z. Szarka, and R. M. Hochstrasser, J. Chem. Phys. 98 6291 (1993) by permission of the American Institute of Physics.]...

Silyl enol ethers, 23, 77, 99-117,128 Silyl enolates, 77 Silyl peroxides, 57 Silyl triflate, 94 Silyl vinyl lithium, 11 (E)-l -Silylalk-1 -enes, 8 Silylalumimum, 8 Silylation, 94 reductive, 26 a-C-Silylation, 113 O-Silylation.99,100 / -SilyIketone, 54 non-cydic, 55 Silylmagnesium, 8 Silyloxydienes, 112 Sodium hexamethyldisilazide, 89 Sodium thiosulphate pentahydrate, 59 Stannylation, see Hydrostannylation Stannylethene, 11 (Z)-Stilbene, 70 (E)-Stilbene oxide, 70 /3-Styryltrimethylsilane, 141 Swern oxidation. 84,88... 

A short and efficient synthetic approach to hydroxy-substituted ( )-stil-benoids, as exemplified by the natural compound resveratrol (371b) via solid-phase CM, was reported by a Korean group (Scheme 71) [154]. When two different stilbenes were allowed to couple by catalyst C, all three kinds of possible stilbenes were obtained as an inseparable mixture. Anchoring 4-vinylphenol to Merrifield resin, followed by exposing the supported styrenyl ether 368 and diacetoxy styrene 369 (10 equiv) to the catalyst, inhibited self-metathesis of the supported substrate. Sequential separation of the homodimer formed from 369 by washing and subsequent cleavage of the resin 370 with acid provided (E)-stilbene 371a with complete stereocontrol in 61% yield. 

Both trans-l amino-2,3-diphenylaziridine and l-amino-2-phenylazi-ridine give a,/S-epoxyhydrazones that fragment in the desired manner between 100° and 200°, the choice of reagent being dictated by the ease of separation of the alkynone from the by-products, (F/)-stilbene and styrene, respectively. The diphenylaziridine is especially useful when the alkynone is relatively volatile and easily separable by distillation from (E)-stilbene, as is the case in the present example. The phenylaziridine... 

The lead tetraacetate reaction between jV-aminophthalimide and (E) stilbene was first described by Rees,5 and the hydrazinolysis of the addition product by Carpino.6 The procedures described here incorporate their methods, with improvements. The dimesylate-hydrazine reaction was first described by Paulsen7 in the carbohydrate series. 

E)-Stilbene, m.p. 123-126°, was purchased from Aldrich Chemical Company, Inc., and was used as received. It is also available from J. T. Baker Chemical Company and from Eastman Organic Chemicals. 

The suspension may be warmed to dissolve the alkene more rapidly. (E)-Stilbene dissolves completely at ca. 65°. If the suspension is warmed, it must be cooled below 30° before proceeding further to prevent a vigorous reaction when the N-bromo-succinimide is added. The submitters recommend that the warm suspension be cooled under an atmosphere of nitrogen. If a volatile alkene is used, the mixture should be cooled prior to and during the addition of N-bromosuccinimide to prevent losses by evaporation. 

The mesoporous character of MCM-41 overcomes the size limitations imposed by the use of zeolites and it is possible to prepare the complex by refluxing the chiral ligand in the presence of Mn +-exchanged Al-MCM-41 [34-36]. However, this method only gives 10% of Mn in the form of the complex, as shown by elemental analysis, and good results are only possible due to the very low catalytic activity of the uncomplexed Mn sites. The immobihzed catalyst was used in the epoxidation of (Z)-stilbene with iodosylbenzene and this led to a mixture of cis (meso) and trans (chiral) epoxides. Enantioselectivity in the trans epoxides was up to 70%, which is close to the value obtained in solution (78% ee). However, this value was much lower when (E)-stilbene was used (25% ee). As occurred with other immobilized catalysts, reuse of the catalyst led to a significant loss in activity and, to a greater extent, in enantioselectivity. 

The uncatalyzed reaction (b) gives predominately the thermodynamically more stable E-stilbene and the ratio of E-stilbene to Z-stilbene is typically 70 30. However, a complete reversal of the selectivity is observed if TiN nano-... 

The photochemical isomerization of E-stilbenes has been applied in the preparation of phenanthrenes, as Z-stilbenes undergo electrocyclie ring closure (cf. chapter 3.1.3) to dihydrophenanthrenes which in turn are easily oxidized to phenanthrenes (3.1) 305). This sequence has also been employed in the synthesis of benzoquinolines 306) or of benzoquinolizines (3.2) 307). 

The synthesis of other biologically active thiazoles was described by Ohsumi et al. [50] and is shown in Scheme 16. Condensation of phosphonium bromide and 4-methoxy-3-nitrobenzaldehyde gave a 1 1 mixture of (Z)- and (-E)-stilbenes. ( )-stilbene 64 was purified by crystallization and then converted to bromohydrin 65 by NBS-H2O. Oxidation of the bromohydrin by DMSO-TFAA gave the bromoketone intermediate 66, which was condensed with thiocarbamoyl compounds in the presence of Na2C03 in DMF to give the corresponding 2-substituted thiazole derivatives (67a and b). Compound 67a... 

An informative set of calculations was carried out by Brandt et al, coupled to experimental studies that demonstrated first-order dependence of the turnover rate on both catalyst and H2, and zero-order dependence on alkene (a-methyl-(E)-stilbene) concentration [71]. The incentive for this investigation was the absence of any characterized advanced intermediates on the catalytic pathway. As a result of the computation, a catalytic cycle (for ethene) was proposed in which H2 addition to iridium was followed by alkene coordination and migratory insertion. The critical difference in this study was the proposal that a second molecule of H2 is involved that facilitates formation of the Ir alkylhydride intermediate. In addition, the reductive elimination of R-H and re-addition of H2 are concerted. This postulate was subsequently challenged. For hydrogenation of styrene by the standard Pfaltz catalyst, ES-MS analysis of the intermediates formed at different stages in the catalytic cycle revealed only Ir(I) and Ir(III) species, supporting a cycle (at least under low-pressure conditions in the gas... 

Scheme 4-51. Asymmetric epoxidation of trans-stilbene with catalyst 135. Substrate (E )-stilbene. Substrate ( )-4,4 -diphenylstilbene. Reprinted with permission by Am. Chem. Soc., Ref. 105a, 106.

In a 50 mL three-necked flask with a magnetic stirrer bar was dissolved (E)-stilbene (181 mg) in acetonitrile-dimethoxymethane (15mL, 1/2, v/v). Buffer (10 mL), tetrabutylammonium hydrogensulfate (15 mg) and ketone catalyst (77.4mg) were added with stirring. 

E)-stilbene was the exclusive product of the Pd colloid-catalyzed Heck arylation of styrene with chlorobenzene. Recently, a polymer-mediated self-assembly of functionalized Pd and Si02 nanoparticles have been found to be highly active catalysts for hydrogenation and Heck coupling... 

The competition between ET and 5n2 processes in the reaction between radical anions of various aromatic compounds, e.g. anthracene, pyrene, (E)-stilbene, and m- and / -cyanotoluene, and substrates such as RHal (where R = Me, Et, Bu, 2-Bu, neopentyl, and 1-adamantyl) or various methanesulfonates has been studied in DMF as solvent. The reaction mechanism could be characterized electrochemically in many of the systems indicated above. The presence of an 5n2 component is related not only to the steric requirements of the substrate, but also to the magnitude of the driving force for the ET process. 

Fig. 6 The typical disorder of CX3 peripheral groups about the pseudo threefold axis left) and the t) pical pedal motion disorder about the central double bond in E-stilbene kind of molecules right)...

Sodium toluene dispersion of, 55, 65 Sodium p-toluenesulfinate, 57, 103 Spiro[4 n] alkenones, 58, 62 Spiro[cyclopentane-l,l -indene] 55, 94 Squalene, 56, 116 Squalene, 2,3-epoxy, 56, 116 Stannic chloride, 56, 97 Steroids synthesis, 58, 85 E Stilbene, 55, 115,58, 73 z-Stilbene, 58, 133 Styrene, 56, 35,58, 43 Styrene glycol, 55, 116 Styrene glycol dimesylate, 55, 116 Succinic acid, 58, 85 Succinic anhydride, 58, 85 Sucunimide, 56, 50, 58, 126 Succimmide, Vbromo, 55, 28, 56, 49 SULFIDE CONTRACTION, 55, 127 Sulfide, dimethyl-, 56, 37 SULFIDE SYNTHESIS, 58, 143,58, 138 SULFIDE SYNTHESIS ALKYL ARYL SULFIDES, 58, 143 SULFIDE SYNTHFSIS DIALKYL SULFIDES, 58, 143 SULFIDE SYNTHESIS UNSYMMETRI-CAL DIALKYL DISULFIDES, 58, 147 SULFONYL CYANIDES, 57, 88 Sulfur tetrafluoride, 57, 51... 

Groups of reportedly photochromic systems which deserve further study include (a) disulfoxides (123,124), (b) hydrazones (125-129), (c) osazones (130-133), (d ) semicarbazones (134-143), (e) stilbene derivatives (144), (/) succinic anhydrides (145-148), and (g) various dyes (149,150). A number of individual compounds also remain unclassified as to their mechanism of photochromic activity. These include o-nitro-benzylidine isonicotinic acid hydrazide (151), 2,3-epoxy-2-ethyl-3-phenyl-1-indanone (152), p-diethyl- and p-dimethyl-aminophenyli-minocamphor (153), brucine salts of bromo- and chloro-nitromethionic acid (154), diphenacyldiphenylmethane (155,156), 2,4,4,6-tetraphenyl-1,4,-dihydropyridine (155,156), 2,4,4,6-3,5-dibenzoyltetrahydropyran (155,156), o-nitrobenzylidenedesoxybenzoin (157), p-nitrobenzylidene-desoxybenzoin (157), N-(3-pyridyl)sydnone (158,159), tetrabenzoyl-ethylene (160), and the oxidation product of 2,4,5-triphenylimidazole (161,162). 

Essentially the same substituents as listed above may be present in the alkene being substituted, with the possible exception of chloro, alkoxy and acetoxy groups on vinyl or allyl carbons. These groups, especially chloro, may be lost or partially lost with palladium when the final elimination step occurs. For example, vinyl acetate, iodobenzene and triethylamine with a palladium acetate-triphenylphosphine catalyst at 100 C form mainly (E)-stilbene, presumably via phenylation of styrene formed in the first arylation step (equation 21 ).6 ... 

Phenanthrene synthesis. Treatment of (Z)-2-chlorostilbenes, available by Wittig reactions with 2-chlorobenzaldehydes, with Riecke activated magnesium in refluxing THF (12 hours) produces phenanthrenes (64-83% yield). (Z)-2-Bromostilbenes are reduced and isomerized to (E)-stilbenes by activated magnesium. The phenanthrene synthesis involves radical intermediates.2... 

Anodic oxidation of tetraphenylethylene at a platinum electrode leads to the product of cyclization, namely, to 9,10-diphenylphenanthrene (Stuart Ohnesorge 1971). The intramolecular coupling reaction does not occur when diphenylethylenes, i.e., stilbene and its methyl derivatives, are electrolyzed under the same conditions (Stuart Ohnesorge 1971). This difference in the anodic behavior of these substances was attributed to the low stability of the cation radicals of stilbene and its methyl derivatives in comparison to the cation radicals of tetraphenylethylene. The participation of the cation radicals in cyclization of tetraphenylethylene has been unequivocally proved (Svanholm et al. 1974 Steckhan 1977). 

Galli, S Mercandelli, P. Sironi, A. Molecular Mechanics in Crystalline Media the Case of (E)-Stilbenes. J. Amer. Chem. Soc. 1999, 121, 3767. 

Fig. 11. Energy level diagram for the (E)-stilbene (S) excited singlet and triplet states, the (E)-stilbene-fumaronitrile (FN) exciples, and triplet fumaronitrile [165, 166]...

E-Stilbene (18 mg, 0.1 mmol) and ketone (3.8 mg, 0.01 mmol) were dissolved in CH3CN (1.5 mL) at r.t. An aqueous Na2(EDTA) solution (1 mL, 4 x 10-4 M) was added. To the stirred mixture was added in portions a mixture of Oxone (307 mg, 0.5 mmol) and sodium bicarbonate (130 mg, 1.55 mmol). On completion of the reaction according to TLC analysis (20 min), the reaction mixture was poured into water (20 mL) and extracted with CH2CI2 (3 x 20 mL). The combined organic layers were dried over anhydrous Na2S04. After removal of the solvent under reduced pressure, the residue was purified by flash column chromatography on silica gel (hexane, then 95 5 hexanes ethyl acetate) to give trans-stilbene epoxide (19.4 mg, 99% yield) in 47% ee. 

E-Stilbene (0.181 g, 1 mmol) was dissolved in 1 2 acetonitrile DMM (15 mL). To this solution were added buffer (10 mL, 0.05 M solution of Na2B4O7l0H2O in 4 x 10-4 M aqueous Na2(EDTA)), tetrabutylammonium hydrogen sulfate (0.015 g, 0.04 mmol), and ketone catalyst (77.4 mg, 0.3 mmol). The mixture was cooled in an ice bath. A solution of Oxone (0.85 g, 1.38 mmol) in aqueous Na2(EDTA) (4 x 10-4 M, 6.5 mL) and a solution of K2CO3 (0.8 g, 5.8 mmol) in water (6.5 mL) were added dropwise separately over a period of 1.5 h (via syringe pumps or addition funnels). The best results were obtained if these solutions were added in a steady, uniform manner. After 2 h, the reaction was diluted with water (30 mL), and extracted with hexanes (4 x 40 mL). The combined extracts were washed with brine, dried (Na2S04), filtered, concentrated, and purified by FC on silica gel (previously buffered with 1% triethylamine solution in hexane) using 1 0 to 50 1 hexane ether as eluent. This provided trans-stilbene oxide (0.153 g, 78%) with 98.9% ee. 

Gilman and coworkers220 229 235,243 found that PhsGeLi could be added to 1,1-diphenylethylene, 1 -octadecene and benzalacetophenone (but not to 1 -octene, cyclohexene and E-stilbene). The reaction of Ph3GeLi with enolizable ketones followed equation l244. 

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