2-aryl-3-ethenyl

It may be suspected that the genuinely topotactic (as secured by the molecular precision of the AFM [18]) photodimerization of 2-benzyl-5-benzyli-denecyclopentanone [118] might be a good candidate for a quantitative preparative photo dimerization to give the head-to-tail anti-[2+2] dimer. Early quantitative solid-state [2-1-2] photodimerizations (most of the published mechanistic interpretations of which can no longer be accepted) are listed in [110]. These deal with the anti dimerization of acenaphthylene-1,2-dicarboxylic anhydride, the head-to-head syn dimerization of acenaphthylene-1-carboxylic acid, the syn dimerization of 5,6-dichloroacenaphthylene, and the thermally reversible head-to-tail anti dimerization of seven ( )-2,6-di-f-butyl-4-(2-aryl-ethenyl)pyrylium-trifluoromethanesulfonates. All of these reactions proceed fully specific. On the other hand, quantitative photoconversions of a 1 1 mixed crystal of ethyl and propyl a-cyano-4-[2-(4-pyridyl)ethenyl]cinnamates gives mixtures of diesters with one (A>410 nm) or two cyclobutane rings (no cutoff filter). 

Aryl-ethenyl-sulfoxide reagieren in Gegenwart basischer Katalysatoren, z.B. Natriumhy-drid4oder l,5-Diaza-bicyclo[5.4.0]undec-5-en5, unter Michael-Addition mit 2-Nitro-pro-pan zu Aryl-(3-methyl-3-nitro-butyl)-sulfoxiden. So reagiert (4-Chlor-phenyl)-ethenyl-sulfoxid zu (4-Chlor-phenyl)-(3-methyl-3-nitro-butyl)-sulfoxid (85%)4,5 ... 

Arenetellurolates, ethenetellurolates, and alkanetellurolates prepared by reduction of diorgano ditellurium compounds with sodium borohydride in ethanol, THF/ethanol, or DMSO add to acetylenes in regioselective and iran.y-stereoselcctive reactions to produce aryl ethenyl tellurium products either predominantly or exclusively as (Z)-isomers. The yields are almost always higher than 70%. In reactions with acetylenic aldehydes, ketones, carboxylic acids, and esters the arenetellurolate becomes bonded to the carbon atom in a [i-position to the carbonyl group. 

An alternative indirect but efficient method for the bromination of all three groups of tri(primaiy alkyl)boranes involves initial reaction with mercury(II) acetate followed by in situ bromination. Alkenyldialkylboranes react with bromine to give bromoalkenes via an addition-elimination mechanism. The meftod of elimination controls the stereochemistry of the product bromoalkenes (Scheme 1). For reasons which are not clear, exactly opposite stereochemical results are obtained from (aryl-ethenyl)dialkylboranes as compared with (alkylethenyl)dialkylbotanes (Scheme 1). ... 

Photoinduced intramolecular cyclization of aryl-ethenyl systems to produce aromatic compounds is a very common process (see reference 43 for reactions to give aliphatic products). Over the years, the reaction has been observed for an extremely wide range of compounds and has been used in numerous synthetic pathways. Schultz has recently published two excellent reviews pertinent to this area. One article deals with photochemical six-electron... 

Grellmann and co-workers, who have contributed considerably to this area with their work on the photocyclization of diarylamines to carbazoles, now report that the only unknown isomer (157) of the five possible indolocar-bazoles can be conveniently synthesized from (158) in methylcyclohexane solution by using 300 nm radiation.Flash experiments and steady-state studies show that the formation of (157) occurs adiabatically in the triplet manifold by a two-photon process and a triplet energy transfer reaction prevents accumulation of large concentrations of the intermediate photoproduct (159). Photocyclization of the aryl-ethenyl compounds (160) has been... 

Examples of aryl ethenyl tellurium compounds prepared in this manner are given in Table 12 (p.403). 

C,C-Doppelbindungenin der Herstellung von 3-Aryl-5-(2-aryl-ethenyl)-234 bzw. 4-(2-Alkenyl)-1 H-pyrazolen270... 

Likewise, addition of aryl-, vinyl-, and alkyllithium reagents to tetrahydro-2-[2-(phcnylsul-fonyl)-2-(trimethylsilyl)ethenyl]-2tf-pyran followed by desilylation gives the. syn-products12 13. 

The question of configurational stability has been investigated first for vinylidene carbenoids and, more recently, for alkylcarbenoids. Vinyl anions are usually considered to be configurationally stable" ° the calculated inversion barrier of the ethenyl anion 10 (R = H) is about 35 kcal mol (equation 4)" . Concerning lithioalkenes, this configurational stability has been confirmed experimentally for a-hydrogen, a-alkyl and a-aryl substituted derivatives . The inversion of vinylidene lithium carbenoids was already... 

Allyl and propargyl halides participate in the Michaelis-Arbuzov reaction, though isomerization is sometimes observed. The Michaelis-Arbuzov reaction of alkynyl halides (15, Scheme 8) is synthetically useful when the alkyne is suitably substituted (e.g. Scheme 8, R2 = aryl, substituted ethenyl, Me3Si, Et3Sn, Cl, X = Cl, Br) and the area has been reviewed.37... 

Hydroxylamin N-(4-Ethenyl-tetrafluor-phenyl)- E16a, 6 (N-Aryl.)... 

Ethyl-2-oxo-4-(2-phenyl-ethenyl)-E16b, 243 (Nitril + RCH2-COOR), 570 (N-Aryl-Bindungsspaltung)... 

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