Ryuzo Asano

Aromatic substitution of olefins. VI. Arylation of olefins with palladium(II) acetate

Olefins react with benzene derivatives to produce aryl-substituted olefins uia direct substitution of the aromatic compound for hydrogen on the double bond of the olefin in the presence of palladium salts and reduced palladium metal. The reaction may be made catalytic with respect to the palladium salts by using cupric acetate or silver acetate, and air as reoxidants. The reaction provides an extremely convenient method for the synthesis of a wide variety of olefinic compounds. xtensive studies on reactions of olefins in the presE ence of transition metal compounds have been carried out. Much less is known about arylation of olefins with transition metal compounds. Most recently, Heck described interesting arylation reactions of olefins with arylating agents such as arylmercuric halides in the presence of group VI11 metal salts, and showed that palladium salts are the most generally useful, with rhodium and ruthenium salts next best. We have reported a novel method of synthesizing stilbene derivatives by substitution of aromatic compounds for hydrogen on the double bond of the styrenepalladium chloride ~ o m p l e x . ~ In the course of our work, palladium acetate was found to be the most effective for the direct arylation of olefins with aromatic compounds in the presence of acetic acid. The present paper reports a study of substitution reaction of olefins with benzene derivatives by means of palladium salts, especially palladium acetate. A preliminary communication of a portion of this work has been given.4 ( I ) On leave of absence from Ube Industries, Ltd., Ube, Japan. (2) (a) R. F. Heck, J . Amer. Chem. Soc., 90, 5518 (1968); (b) R .F. Heck, ibid., 90, 5526 (1968); (c) R. F. Heck, ibid., 90, 5531 (1968); (d) R. F. Heck, ibid., 90, 5535 (1968); (e) R. F. Heck, ibid., 90, 5542 (1968). (3) (a) I. Moritani and Y. Fujiwara, Tefrahedron L e f f . , 1119 (1967); (b) Y . Fujiwara, I. Moritani, and M. Matsuda, Tetrahedron, 24, 4819 (1968). (4) Y. Fujiwara, I. Moritani, M. Matsuda, and S . Teranishi, Tetrahedron Lett., 633 (1968). Results and Discussion In previous papers3 we described our initial work on the reactions of the styrene-palladium(I1) chloride complex with benzene derivatives to give stilbenes. It was noted that for this arylation on a P-carbon atom of styrene, the presence of a carboxylic acid such as acetic is essential because the reactants form a homogeneous solution and the reaction proceeds best in this solvent. Further, it was found that when sodium acetate was added, the yield was greatly increased. Palladium(I1) acetate has been found to be the most generally useful, with palladium(I1) chloride-sodium acetate next best for the direct arylation of olefins with benzene derivatives. The aromatic substitution of olefins takes place in homogeneous solutions of reactant olefin and palladium(I1) acetate (equal mole equivalents to olefin) in a solution of the aromatic compound (large excess) and acetic acid. The solution is stirred in the presence of air for a few minutes to several hours (8 hr usually), to give from 10% to ca. 90% yield of arylated products, with reduced metallic palladium and a very small amount of acetates. With unsymmetrical olefins, the aryl group generally adds predominantly to the less substituted carbon atom of the double bond because of steric hindrance of the substituents. This is consistent with that observed in the Heck arylation.2 Although cis and trans mixtures are formed, no mixtures resulting from arylation in both directions to unsymmetrical olefins have been found. Increasing substitution on the olefinic carbons decreases the reactivity of the olefin in the palladium acetate arylation reaction. For example, the reaction of triphenylethylene with benzene and a palladium acetate catalyst gave tetraphenylethylene in low yield (13 %),5 while styrene reacts with benzene to afford trans-stilbene in almost quantitative yield. Results are given in Table I. (5) Yields of arylation products given in this paper are based on the amount of palladium salt utilized. Journal of the American Chemical Soc ie t y J 91:25 December 3, 1969

Aromatic substitution of olefin—VIII : Substituent effects on the reactions of styrene with monosubstituted benzenes in the presence of palladium(II) salts

Abstract In the reactions of styrene with monosubstituted benzenes such as toluene, ethylbenzene, anisole or chlorobenzene in the presence of palladium(II) salts, the direction of substitution but not the reactivity is strongly influenced by the substituent on a benzene ring.

Aromatic substitution of olefins. Part XVII. Reactions of ferrocene with olefins in the presence of palladium(II) salts

Ferrocene reacts with olefins to produce alkenylferrocenes in the presence of palladium(II) acetate. The reactivity of the olefin is strongly influenced by substituents: it is increased by electron-withdrawing groups. The reaction provides a convenient synthesis of ferrocene derivatives.

Aromatic substitution of olefins. The reaction of ferrocene with styrene in the presence of palladium(II) acetate

Ferrocene reacts with styrene to produce trans-α-styrylferrocene in the presence of palladium(II) acetate, which exemplifies an extremely convenient method for the direct synthesis of alkenylferrocenes.