Halides vinyl substitutions

Stannyl cuprates couple widi vinyl halides or trlGales [16c-d, 85], and a vinyl stannane produced diis way has been used in die syntliesis of 7-[f )-alkylidetie]-cepbalosporlns [117]. Vinyl substitution reactions slariing Grom ddiydrofciraiis are... 

A complementary approach for cross-couplings with allenes was applied by using metallated allene species instead of allenyl halides, which have already been discussed in Sect. 14.2.1. Since allenyllithium compounds are readily available by deprotonation of allenes with n-butyllithium, successful cross-coupling reactions between lithiated allenes such as 54 or 57 and aryl or vinylic halides allowed convenient routes to aryl- and vinyl-substituted allenes, e.g. 55, 58 and 60 (Scheme 14.15) [30],... 

The olefinic substitution reaction may also be effected in some instances by using a palladium(II) salt and an aromatic compound instead of an organic halide. Palladium(II) salts are apparently able to metallate some aromatic hydrocarbons directly. The reaction succeeds best with aromatics activated with electron-supplying substituents producing, with certain olefinic compounds, vinylically substituted products. For example, benzene and styrene with palladium acetate in boiling acetic acid produce stilbene in 90% yield (37). 

With other vinylic halides, the substitution pattern determines the direction of HBr addition (equations 79—83).61,65,128-136... 

VINYL SUBSTITUTION WITH ORGANIC HALIDES, DIAZONIUM SALTS, ACID CHLORIDES, 842... 

Vinyl Substitution with Alkyl, Aryl and Vinyl Halides 842... 

Vinyl Substitutions with Carboxylic Acid Halides, Aryl Sulflnates and Arylsulfonyl Chlorides 856... 

The vinyl substitution reaction often may be achieved with catalytic amounts of palladium. Catalytic reactions are carried out in different ways depending on how the organopalladium compound is generated. Usually copper(II) chloride or p-benzoquinone is employed to reoxidize palladium(0) to palla-dium(II) in catalytic reactions when methods (i) or (ii) are used for making the organopalladium derivative. The procedures developed for making these reactions catalytic are not completely satisfactory, however. The best catalytic reactions are achieved when the organopalladium intermediates are obtained by the oxidative addition procedures (method iii), where the halide is both the reoxidant and a reactant. Reviews of some aspects of these reactions have been published.u-le... 

Normally, the most practical vinyl substitutions are achieved by use of the oxidative additions of organic bromides, iodides, diazonium salts or triflates to palladium(0)-phosphine complexes in situ. The organic halide, diazonium salt or triflate, an alkene, a base to neutralize the acid formed and a catalytic amount of a palladium(II) salt, usually in conjunction with a triarylphosphine, are the usual reactants at about 25-100 C. This method is useful for reactions of aryl, heterocyclic and vinyl derviatives. Acid chlorides also react, usually yielding decarbonylated products, although there are a few exceptions. Likewise, arylsulfonyl chlorides lose sulfur dioxide and form arylated alkenes. Aryl chlorides have been reacted successfully in a few instances but only with the most reactive alkenes and usually under more vigorous conditions. Benzyl iodide, bromide and chloride will benzylate alkenes but other alkyl halides generally do not alkylate alkenes by this procedure. 

Alkyl halides with (3-hydrogens generally undergo only elimination reactions under the conditions of the vinyl substitution (100 C in the presence of an amine or other base). Exceptions are known only in cases where intramolecular reactions are favorable. Even alkyl halides without (3-hydrogens appear not to participate in the intermolecular alkene substitution since no examples have been reported, with the exception of reactions with benzyl chloride and perfluoroalkyl iodides. 

Very few examples of vinyl substitution with polynuclear aromatic halides have been reported but indications are that they generally react like the halobenzenes. 

Further examples of the vinyl substitution reaction with aryl halides are given in Table 1. 

Vinyl substitution of primary or secondary allylic alcohols with aryl halides usually produces 3-aryl aldehydes or ketones, respectively. The reaction is believed to involve an addition of the intermediate arylpalladium halide to die double bond, placing the aryl group mainly on the more distant carbon from the hydroxy group, followed by palladium hydride elimination, a reverse readdition and another elimination with a hydrogen atom on the carbon bearing the hydroxy group. The product is probably a ir-com-plex of the enol which ultimately either dissociates or collapses to a a-complex with palladium on the... 

In 1991, we reported that a nucleophilic vinylic substitution of (E)-fi-alkylvinyl-AModanes with halides (BuN4X, X = C1, Br, I) in dichloromethane, methanol, or acetonitrile at room temperature proceeds with exclusive inversion of configuration [Eq. (100)] [176,177]. This is the first clear example of a vinylic Sn2 reaction. This reaction competes with an alkyne-forming reductive syn /3-elimination. 

Cacchi, S. Fabrizi, G. Gasparrini, F. Pace, P. Villani, C. The utilization of supercritical C02 in the Pd-catalyzed hydroarylation of /i-substi-tuted-a,/i-enones. Synlett 2000, 650-652. Amorese, A. Arcadi, A. Bemocchi, E. Cacchi, S. Cerrini, S. Fedeli, W. Ortar, G. Conjugate addition vs vinylic substitution in Pd-catalyzed reaction of aryl halides with /i-substituted-a, /i-enones and -enals. Tetrahedron 1989, 45, 813-828. 

---