Friedel-Crafts alkenylation

Sames et al. studied the cyclization of phenyl/propargyl ethers catalyzed by different metal salts since this Friedel-Crafts alkenylation had previously been reported to be catalyzed by metals such as Pd, Zr In and Sc [122-124] or even zeolites by hereogeneous catalysis [125]. In this preliminary research, the maximum yield of the desired product achieved by gold was only 6%, the best results being obtained with PtCl2 as catalyst [126]. 

Friedel-Crafts alkenylation of arenes with various phenylacetylenes to yield 1,1-diarylalkenes was reported. Alkyl-substituted benzenes and naphthalene react with phenylacetylene in the presence of zeolite HSZ-360 to afford the products in good to excellent yields and selectivities 415... 

Friedel-Crafts alkenylation involving the triple bond of an o-isothiocyanatoarylalkyne and initiated by InBr3 [or In(OTf)3] leads to a 4-substituted quinoline-2-thione. Best results are obtained from alkynes with a t-butyl group at the other end of the triple bond (which is lost during the reaction). 

The use of ionic liquids as solvents dramatically increased the catalytic activity of Sc(OTf)3, and it exhibited unusually high activity for Friedel-Crafts alkylation of aromatic compounds with linear or cyclic olefins in imidazolium-based hydrophobic ionic liquids such as [EMIm]SbF6, [BMIm]PF6, and [HMIm]PF6. It should be noted that no reaction occurred in common organic solvents, water and hydrophilic ionic liquids [45]. This kind of activity enhancement of Sc (OTf) 3 by means of ionic liquid solvents was also observed in the Friedel-Crafts alkenylation of arenes with alkynes [46]. 

Friedelr-Crafts Alkenylation. Hf(OTf)4 jointly used with an ionic liquid catalyzed the Friedel-Crafts alkenylation of arenes. Moreover, the ionic liquid phase containing catalyst could he readily recovered by simple decantation of the organic layer after reaction and reused for the following runs without any significant loss of activity (eqs 19 and 20). ... 

A simple and practical Cu(OTf)2-catalyzed synthesis of quinoline-2-carboxylates through tandem Grignard-type imine addition/Friedel-Crafts alkenylation of arenes with aryl or alkyl alkynes via activation of C-H bonds was reported in 2009 (Scheme 8.84). The quinoline-2-carboxylates products could be obtained in high yields from a number of readily available alkynes and imines at room temperature [154]. 

Alkenyl halides such as vinyl chloride (H2C=CHC1) do not form carbocations on treatment with aluminum chloride and so cannot be used m Friedel-Crafts reactions Thus the industrial preparation of styrene from benzene and ethylene does not involve vinyl chloride but proceeds by way of ethylbenzene... 

This section will describe the Friedel-Crafts alkylation reactions of aromatic hydrocarbons with alkenylchlorosilanes containing short chain alkenyl groups such as allyl and vinyl. The reaction will be discussed in terms of the substituent effect on silicon and the arene rings. 

Friedel-Crafts cyclization of alkenyl acid chlorides affords mixtures of tetrahydro- and dihydro-thiopyrans (equation 76) (80JHC289). 

A short review in Chinese covers Friedel-Crafts reactions of alkenyl halides with aromatic hydrocarbons.49 High yields of the allylated aromatic products have been... 

When ( )-[(/i-arylethyl)vinyl]phenyliodonium tetrafluoroborates are heated in various solvents (at 40 °C or 60 °C), Friedel-Crafts cyclizations occur and dihydronaphthalenes are obtained (equation 26l)127. 6-Bromo-2i7-chromene can be prepared in the same way (equation 262). The alkenylation of benzene with 4-rm-butyl-1 -cyclohexenyl-(phenyl)iodonium tetrafiuoroborate, an intermolecular version of these reactions, has also been demonstrated (equation 263)127. From a stereochemical standpoint, the cyclization reactions are constrained to occur with inversion of configuration at vinyl carbon, while the cyclohexenylation of benzene must proceed with retention. 

We found that Friedel-Crafts alkylation of CTM or CTR was possible, as well as acylation [364). In this manner, a number of CTM homologs were obtained (365-367). Dehydration of the CTM alcohols gave us the alkenyl derivatives. Reduction of the acylated derivatives and use of Grignard reactions were a source of secondary and tertiary alcohols whose dehydration gave us the alkenyl derivatives [Nesmeyanov, Anisimov, Kolobova, Zlotina (368, 369)]. 

The well-established stabilization of a positive charge on carbon p to silicon has been utilized in very versatile methods for the control of aliphatic Friedel-Crafts reactions. The specificity of this stabilization lies behind the utility of both alkenyl- and allyl-silanes as substrates for electrophilic substitutions, and acylations in particular. These classes offer complementary regiospecificities in controlling both the site of acylation and the location of the double bond. This promotion of simple substitution is one of the most significant advances in aliphatic Friedel-Crafts acylations of recent times, and has recently been the subject of an exhaustive review. ... 

The P-effect of silicon tends to direct the site of electrophilic attack on alkenylsilanes to the carbon bearing the silicon atom (Scheme 4). In comparison with a proton, the greater ease with which the tri-methylsilyl group is displaced from carbon leads more often to the formation of substitution products rather than those of addition. Thus vinyltrimethylsilane (b.p. 55 °C) is a convenient equivalent for ethylene in Friedel-Crafts acylations. The alkenyl ketone is formed directly, in contrast to the p-chloroethyl ketone formed in the acylation of ethylene. 

Despite the lack of examples of Friedel-Crafts acylations catalyzed by Lewis acids, - reactions of stannanes with acyl halides catalyzed by palladium species have found considerable use for the preparation of ketones. Since alkyl groups are only transferred slowly from tin, more rapid transfer to the acyl chloride is observed for alkynyl, alkenyl and allyl, as well as aryl and benzyl, groups. This leads to a versatile synthesis of ketones.Acylations of alkenylstannanes are both regio- and stereo-specific. 

Metal-catalyzed hydroarylation of alkynes catalyzed by electrophilic transition metal complexes has received much attention as a valuable synthetic alternative to the Heck and cross-coupling processes for the synthesis of alkenyl arenes (384). Metal trifluoromethanesulfonates (metal triflates) [M(OTQn M = Sc, Zr, In] catalyze the hydroarylation of alkynes via 71 complexation to give 1,1-diarylalkenes in very good yields (Scheme 32) (385). The reaction likely proceeds by a Friedel-Crafts mechanism via the alkenyl cation intermediate where the aryl starting material also serves as the solvent. 

Nazarov-Friedel-Crafts reaction tandem. l-Alkenyl-2,2-dichlorocyclopropyl... 

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