Vinyl compounds aryl substituted

The stereochemistry of addition is usually anti for alkyl-substituted alkynes, whereas die addition to aryl-substituted compounds is not stereospecific. This suggests a termo-iecular mechanism in the alkyl case, as opposed to an aryl-stabilized vinyl cation mtermediate in the aryl case. Aryl-substituted alkynes can be shifted toward anti addition by including bromide salts in the reaction medium. Under these conditions, a species preceding the vinyl cation must be intercepted by bromide ion. This species can be presented as a complex of molecular bromine with the alkyne. An overall mechanistic summary is shown in the following scheme. 

The Heck reaction consists in the Pd(0)-catalysed coupling of alkenes with an aryl or alkenyl halide or triflate in the presence of a base to form a substituted alkene (Scheme 7.1). The reaction is performed in the presence of an organopalladium catalyst. The halide or triflate is an aryl or a vinyl compound and the alkene contains at least one proton. 

Gallium(III) triflate catalysed the rearrangement of 2-substituted vinyl epoxides into /3,y-unsaturated carbonyl compounds with high regio- and chemo-selectivity with low catalyst loading. Alkyl-substituted trimethylsilylvinyl epoxides gave /i,y-unsaluralcd ketones, but aryl-substituted vinyl epoxides gave the aldehydes.80... 

The most simple a-aryl substituted vinyl halide studied, a-bromostyrene, flash photolytically yields the enol of acetophenone in aqueous solution, which has been used to measure rates of ketonization302,303. With a,/2-diarylvinyl halides, loss of the /2 (vinylic) proton from the intermediate vinyl cation is competitive with nucleophilic trapping Irradiation of compounds such as 96 in methanol gives about equal amounts of tolan and... 

The majority of the more important methods for the preparation of fluorinated compounds by substitution reactions have been reviewed in the previous sections. There are, however, some additional important synthetic procedures which should also be mentioned, mainly those concerned with the introduction of fluorine by substitution of functional groups containing boron, silicon and tin the reactions of organotin compounds are the most well-studied to date. These reactions are excellent synthetic methods for obtaining vinyl and aryl fluorides (sec also Section 1.1.1.1.). 

The formal addition of perfluorinated pyridine, pyrimidine, pyridazine or of pentafluorobenzo-nitrile to fluorinated acetylenes in the presence of cesium fluoride in sulfolane leads to fluorinated aryl-substituted alkenes. " In the first reaction step fluoride ion adds to the fluorinated acetylene to give a vinyl carbanion, which substitutes, in a second step, a fluoride ion from the perfluorinated aromatic compound. Some examples of this type of reaction are shown by the formation of... 

Indene can participate as the cne component in [4 + 2] and [2 + 2] cycloaddition reactions with diazene dicarboxylates and triazolediones. Aryl-substituted alkenes, however, can participate as the diene components in cycloaddition reactions with the same diazene compounds, although the reaction can follow different pathways depending on the nature of the substituents on the vinyl and phenyl groups. 

The substitution of aluminum by oxygen can be effected by various peroxide derivatives, such as di-r-butyl peroxide, benzoyl peroxide and r-butyl perbenzoate. The main reaction is accompanied by telltale free-radical side reactions, such as the formation of RR from R3AI, which become major pathways with aryl and vinyl compounds. Oxidation of alkenyl derivative (56) with r-butyl perbenzoate yields 45% of a mixture of cis and trans ethers (57 equation 44). As of yet there is no generally applicable, highly efficient method for oxidizing vinylaluminum compounds. 

This chapter surveys the reduction of saturated alkyl halides to alkanes. Reductive -eliminations of vicinal dihalides to alkenes are also described briefly. Reduction of vinyl and aryl halides is covered in this volume. Chapter 4.5 hydrogenolysis of allyl and benzyl halides is covered in this volume. Chapter 4.7, and reduction of a-halo-substituted carbonyl compounds CX—CO to carbonyl compounds CH—CO is covered in this volume. Chapter 4.8. 

The alkyl- and aryl-substituted vinyl azides discussed above are all reasonably stable at room temperature. However, the introduction of strongly electron-withdrawing substituents on the double bond appears to facilitate thermal decomposition of these compounds. A number of azides thus substituted have been found to decompose at room temperature or belo. v. 

In addition, the vinyl radical can rearrange, before accepting an electron and a proton, to afford either a cis or trcms alkene as a final product. Among compounds that have been investigated are aryl-substituted vinyl bromides [96], cis- and tra w-3-iodo-3-hexene [97], bromomaleate and bromofumarate [98], and aryl-substituted 3-chloroacrylonitriles [99]. Yoshida and coworkers [100] electrolyzed vinyl halides at platinum in DMF in the presence of trimethylchlorosilane to obtain silylation products. 

The Suzuki reaction provides a versatile, general method for the stereo- and regiospe-cific synthesis of conjugated dienes, enynes, aryl substituted alkenes, and biaryl compounds via Pd-catalyzed cross-coupling of vinyl halides or aryl halides with... 

The simplest member of the class of vinyl azides, H2C=CH-N3, has been known for about 100 years. However, it was not until the late 1960s that vinyl azides became an important and synthetically useful class of organic compound. The most interesting and important reaction of vinyl azides is the formation of azirines produced upon photolysis and thermolysis of vinyl azides. Smolinsky and Pryde first observed azirine formation, together with a small amount of keteneimine, by gas-phase pyrolysis of a-aryl-substituted vinyl azides. 

The range of applicability of the Wittig reaction has in recent years become extremely extensive and there have been reports of its use for the preparation of alkyl- and aryl-substituted alkenes, unsaturated aldehydes, ketones, and carboxylic acid derivatives, vinyl halides, and vinyl ethers. In the preparation of these compounds there is often the possibility of cis-trans isomerism Bestmann and Kratzer1003 state that the trans-olefin is always obtained when an alkylidenetricyclohexylphosphorane is used, and Schlosser and Christ-... 

Vinyltin derivatives (92) have been prepared by the reaction of acyltin compounds with phosphonium ylides or with phosphonate carbanions. The tungsten complex (93) reacts with a wide range of aryl-substituted ylides (94), and the vinyl-substituted ylide (95), to give phosphorus to metal alkylidene transfer and hence provides a route to tungsten alkylidene complexes (96). ... 

Intramolecular or intermolecular Heck-type reactions were also used in the synthesis of poly-substituted quinoline compounds. Palladium-catalyzed reaction between vinyl or aryl halides and ortAo-allyl-substituted-A -tosyl-anilides produces dihydroquinolines in an intermolecular fashion, where reaction of acrylates intramolecularly affords 4-quinolones. ° ° ... 

---