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Phenyl-Substituted Alkenes

The diminished stereospecificity is similar to that noted for hydrogen halide addition to phenyl-substituted alkenes. [Pg.300]

Although chlorination of aliphatic alkenes usually gives anti addition, syn addition is often dominant for phenyl-substituted alkenes.33... [Pg.300]

Internal phenyl-substituted alkenes present significant problems for this catalyst system. Although enantioselectivities with both trans (70% ee, Eq. 56) and cis (60% ee, Eq. 58) P-methylstyrene are moderate, cis alkene provides the trans aziridine as the major product. Furthermore, 15% of the recovered alkene is isomer-ized (77). Internal dialkyl alkenes are not prone to this isomerization. [Pg.39]

In a search for more effective approaches to the problem of stereoselective dioxygenation, alternative methods have been developed. While the inclusion of alkenes and O2 within a chiral cyclodextrin cavity furnished hydroperoxides with modest ee values, neighboring stereocenters and chiral auxiliaries could induce highly stereoselective dioxygenation. In 1987 Kropf and Reichwaldt, and three years later Adam and coworkers reported on the photooxygenation of phenyl-substituted alkenes 36 producing allyUc hydroperoxides 37 and 38 with high diastereoselectivity (dr 80/20). In the best example... [Pg.342]

SCHEME 46. Possible interaction of Na+ with phenyl-substituted alkenes within Na-Y... [Pg.877]

Phenyl hydroperoxide, C-O distance, 103 (y-Phenylhydroperoxides, nucleophiUc substitution cyclization, 234-5 1 -Phenyl-3-methyl-3-butene, intrazeohte photooxygenation, 874-5 Phenyl substituted alkenes, photooxidation site selectivity, 839-42... [Pg.1482]

SCHEME 23. Regio- and stereoselective photooxygenation of phenyl-substituted alkenes... [Pg.343]

The reaction of xenon difluoride with a series of cis- and trans-phenyl substituted alkenes was examined in detail. 1,1-Diphenylethene, l,1-diphenyl-2-fluoroethene and 1.1-diphenyl-propene form vicinal 1,2-difluoro derivatives in 65 95% yield in dichloromethane solution with hydrogen fluoride as the catalyst.29-32 Two possible mechanisms were discussed.33... [Pg.223]

Phenyl-substituted alkenes with halogen atoms at the double bond react with xenon difluoride in dichloromethane in the presence of hydrogen fluoride forming vicinal difluorides in 50% yield.35... [Pg.224]

Bromofluorination of phenyl-substituted alkenes. e.g. 1,1 -diphenylethene. /(-alkylstyrenes, stilbene,3h 1-phenylcyclohexene,37 cinnamates, and a-fluorocinnamates,38 with A-bromosuc-cinimide-hydrogen fluoride/pyridine in diethyl ether proceeds with Markovnikov-type re-gioselectivity. The reaction is stereospecilic anti) for E- and nonstereospecific for Z-alkenes due to the large extent of isomerization of the latter under the reaction conditions. [Pg.239]

Bromofluorination of Phenyl-Substituted Alkenes Using the NBS-HF/Pyridine System (Method A) General Procedure 38... [Pg.239]

Chlorofluorination of alkenes and alkynes using the A -chlorosaccharin-hydrogen fluoride/ pyridine system (Method G)50 results in vicinal chlorofluoro-substituted alkanes or alkenes, respectively. Since this system is more reactive than with other A -chloroamides, its use allows shorter reaction times and milder reaction conditions to prepare chlorofluorinated products in higher yields. With phenyl-substituted alkenes, Markovnikov-type adducts are formed exclusively. The additions proceed predominantly anti, with varying degrees of stereoselectivity. [Pg.241]

To overcome problems associated with the removal of iodobenzene and its derivatives formed upon fluorination of arylalkenes and arylalkynes with (difluoroiodo)arenes, polymer-supported (difluoroiodo)arenes were proposed.139 With these agents, the separation procedures are reduced to filtration of the iodinated polymer. For this purpose popcorn polystyrene is io-dinated and then transformed into the difluoroiodide by treatment with xenon difluoride in the presence of hydrogen fluoride in dichloromelhane at 25 C. The amount of active fluorine bonded to iodine atoms on the polymer support is estimated by iodometric titration. The reactions with phenyl-substituted alkenes result in rearranged gew-difluorides. The procedure provides the same fluorination products as with (difluoroiodo)benzenc (see Section 4.13.) but in much higher yields, e.g. PhCF2CH2Ph (96%), PhCF2CH(Me)Ph (95%). PhCH2CF2H (86%), and l,l-difluoro-2-phenylcyclopentanc (91 %). [Pg.261]

The effect of the reagent structure on the fluorination of phenyl-substituted alkenes 6 has been studied in great detail and the higher svn addition observed with trifluoroacetyl hypofluorite in comparison with acetyl hypofluorite explained on the basis of an intermediately formed... [Pg.284]

The regioselectivity in the fluorination of phenyl-substituted alkenes 9 has been reported and in the case of an electron-withdrawing group (C02Me, Ac) and a donating group (4-OMe) a more stable carbenium ion is formed and complete regioselectivity is observed, but it is completely lost in the reaction with the chloro derivative.2... [Pg.285]

The relative reactivity of phenyl-substituted alkenes depends on the structure of the alkene and for reactions in methanol is as follows 10 1,1-diphcnylethene/triphenylethene/tetraphenyl-ethenc/9-benzylidcnefluorene 1.2 1 0.2 0.3. [Pg.297]

The reaction of phenyl-substituted alkenes (2-phenylprop-l-ene, ( )-l-phenylprop-l-ene, 1,1-diphenylethene, 1,1-diphenylprop-l-ene) with F-Teda BF4 (6) in the presence of various alcohols results in the formation of vicinal fluoro alkoxy adducts with Markovnikov-type regioselec-tivity.89,94 The stereochemistry of the fluorination-methoxylation addition reaction is slightly syn predominant in the case of (Z)-stilbene, indene, and dibenzosuberenone, while equal amounts of both diastereoisomers are formed in the case of ( )-l-phenylprop-l-ene and acenaphthylene. [Pg.464]

The stereochemical course of fluorination-methoxylation reactions in the case of cyclic phenyl-substituted alkenes 23 depends strongly on the structure of the alkene.95... [Pg.465]

The reactions of phenyl-substituted alkenes with sodium mirrors yield compounds containing anionic intermediates that may be contact ion pairs with significant Na-C contacts to the alkene skeleton or to phenyl substitu-... [Pg.312]

Electrophilic addition of Cl., and In tn nlkenes is similar in mechanism to the electrophilic addition of Br0.46 The rate of chlorination in acetic acid is second-order, first-order each in olefin and in chlorine.47 Predominantly anti addition to alkyl-substituted double bonds occurs, indicating that a chloronium ion is formed.48 Further evidence for the chloronium ion is that addition of hypo-chlorous acid to double bonds is not entirely regiospecific. For example, addition to propene gives 91 percent of the Markownikoff product 29, and 9 percent of the anti-Markownikoff product, 30. Phenyl-substituted alkenes give a mixture of syn and anti adducts with Cl2 as they do with Br2.49... [Pg.352]


See other pages where Phenyl-Substituted Alkenes is mentioned: [Pg.993]    [Pg.243]    [Pg.81]    [Pg.831]    [Pg.839]    [Pg.876]    [Pg.877]    [Pg.877]    [Pg.1441]    [Pg.1487]    [Pg.1489]    [Pg.373]    [Pg.342]    [Pg.831]    [Pg.876]    [Pg.877]    [Pg.877]    [Pg.465]    [Pg.621]    [Pg.882]    [Pg.373]    [Pg.256]    [Pg.358]    [Pg.371]   


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1-phenyl-1-alkenes

4- Phenyl-7 -substituted

Alkenes phenyl-substituted bicyclic

Alkenes substitution

Phenyl/methyl-substituted alkenes

Regioselectivity phenyl substituted alkenes

Site selectivity phenyl substituted alkenes

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