Heck-type arylation

Heck-type arylation reactions of organobismuth compounds were first reported by Asano et al. in 1973 [11]. This article described the stoichiometric reaction of styrene, Ph3E (E = group 15 elements) and Pd(OAc)2 (Scheme 2). Ph3Bi afforded frans-stilbene only in 7% yield. The major product was biphenyl, which was... 

Aryl cyanides add to norbornene and norbornadiene under nickel catalysis to give (2/U,35 )-3-aryl-2-cyanobicyclo[2.2.11heptanes and (2/U,3.S )-3-aryl-2-cyanobicy-clo[2.2.1]hept-5-enes in good yields with a broad substrate scope. On the other hand, the reaction of an aryl cyanide with triethoxy(vinyl)silane gives a Heck-type arylation product, suggesting the arylnickelation pathway in the catalytic cycle.68... 

Arenediazonium o-benzenesulfonamide 89 was found to be a new and efficient reagent for the Heck-type arylation reactions of some common substrates containing C-C multiple bonds, i.e., ethyl acrylate, acrylic acid, acroleine, styrene, and cyclopentene <2006T3146>. The reactions are carried out in the presence of Pd(OAc)2 and afford arylated products, for example ethyl cinnamates, cinnamic acids, cinnamic aldehydes, and stilbenes, possessing an ( -configuration, and 1-arylcyclopentenes, in good to excellent yields (Equation 27). 

The palladium-catalyzed arylation and alkenylation of olefins, which were first discovered in the 1970 s by Heck (7,2) and Mizoroki (3) and have been often called the "Heck reaction", are versatile synthetic means for making a carbon-carbon bond. These reactions have been extensively used for organic synthesis during the past two decades (4-7). However, no reports on the "asymmetric Heck reaction" have been appeared until very recently. Shibasaki reported an asymmetric intramolecular cyclization of alkenyl iodides to give c/j-decalin derivatives of 80-91% ee (8-10). Overman reported an intramolecular cyclization of alkenyl triflate, giving a chiral quaternary carbon center of 45% ee (77). We report herein the first example of intermolecular asymmetric Heck-type arylation of cyclic olefins catalyzed by (7 )-BINAP-coordinated palladium complexes (Scheme 1) (12,13). 

Because many 4-benzylpiperidines are physiologically and pharmacologically active, an efficient route to these compounds was developed <03TL8249>. Cyclization of imines containing an allylsilane with aldehydes in a one-pot reaction resulted in 4-methylenepiperidines in good yields. Heck-type arylation of arylboronic acids with 4-methylenepiperidines afforded the styryl derivatives, which gave the desired piperidines on reduction. 

Catalytic asymmetric arylation of alkenes.4 This arylation can be effected by a Heck-type arylation of 2,3-dihydrofuran with an aryl triflatc catalyzed by Pd(OAc)2/(R)-BINAP in the presence of 1,8-bis(dimelhylamine)naphthalcnc (proton sponge) as base. This reaction was used to prepare an antagonist (4) of platelet activating factor. 

For an interesting application of a cyclopropanolate as a homoenolate in a Heck-type arylation see F. A. Khan, R. Czerwonka, H.-U. Reissig, Synlett 1996, 533-535. 

It has been found that treatment of propiophenone with an excess amount of bromobenzene gives rise to l,2,3-triphenyl-2-propen-l-one (Eq. 11) [43]. In this reaction, a-arylation, unsaturation via -hydrogen elimination, and Heck-type arylation occur successively. From the reaction of butyrophenone is obtained the corresponding triarylated product (Eq. 12). The reaction sequence involves a-arylation, unsaturation via p-hydrogen elimination, two times vinyl-ogous arylation (y-arylation), and double bond isomerization. It should be noted that a,p-unsaturated carbonyl compounds are generally arylated at their y position (Eqs. 13 and 14) [54-56]. 

The 1,2-insertion of alkenes into transition metal-carbon o-bond leads to C-C bond formation under mild conditions, as described in Chapter 6. This reaction is considered to be a crucial step in the coordination polymerization and carbometalation of alkenes catalyzed by transition metal complexes. A common and important carbometalation is the Heck-type arylation or vinylation of alkene catalyzed by Pd complexes [118], The arylation of alkene, most typically, involves the formation of arylpalladium species and insertion of alkene into the Pd-aryl bond as shown in Scheme 5.20. The arylpalladium species is formed by the oxidative addition of aryl halides to Pd(0) complexes or the transmetalation of aryl compounds of main group metals with Pd(II) complexes. Insertion of alkene into the Pd-aryl bond produces 2-arylalkylpalladium species whose y6-hydrogen elimination leads to the arylalkene. Oxidative chlorination of the 2-arylalkylpalladium intermediate forms chloroalkanes as the product. 

Sugihara, T., Satoh, T. and Miura, M. (2005) Mizoroki Heck type arylation of alkenes using aroyl chlorides under base-free conditions. Tetrahedron Lett., 46, 8269-71. 

An early report on a nickel-catalysed Mizoroki-Heck-type arylalion of an alkene was disclosed by Chiusoli et al. [28] while studying syntheses of linear, deconjugated unsaturated acids (Scheme 10.7). However, in this report, only one particular alkene, namely potassium salt 20, was employed. This substrate is supposed to promote the Mizoroki-Heck-type arylation through precoordination to the transition metal catalyst. From a mechanistic viewpoint it is interesting to note that the nickel catalyst did not require the use of a stoichiometric, relatively strong reducing agent (see below). 

An early platinum-catalysed Mizoroki-Heck-type arylation of an alkene with an organic halide was accomplished with [Pt(COD)Cl2] (54) as metal precursor and PPhs (35) as ligand (Scheme 10.17) [43]. Relatively high reaction temperatures, an inorganic base and... 

Scheme 10.19 Platinum-catalysed intermolecular Mizoroki-Heck-type arylation of styrene...

Scheme 10.21 Cobait-cataiysed Mizoroki-Heck-type arylation under biphasic reaction...

An early report on rhodium-catalysed Mizoroki-Heck-type arylations of alkene 20 using two alkenyl bromides was disclosed by Chiusoli et al [28], Thus, catalytic amounts of [RhCl(PPh3)3] (84) allowed for conversion of potassium 3-butenoate (20) (Scheme 10.28), a substrate that can potentially direct the rhodium catalyst through coordination of its carboxylate group. 

The present section summarizes reductive Mizoroki-Heck-type arylations-that is, palladium-catalyzed hydroarylation reactions of alkenes-which are essentially limited to (hetero-)norbomenes (Section 7.3.2). It should be noted however, that only a handful of remarkable examples are known that are not based on the bicyclo[2.2.1]heptane framework (see Section 7.3.3). 

Scheme 7.35 Simplified catalytic cycle of reductive Mizoroki-Heck-type arylations.

Extension of the asymmetric hydroarylation to oxanorbornenes, as well as aza-norbornenes, was the obvious step forward. Fiaud et al. made several remarkable observations while examining the reductive Mizoroki-Heck-type arylation of the annulated 7-oxanorbornene 160 (Scheme 7.37) [100]. First, intermediate o-aUcyl... 

Reductive Mizoroki-Heck-Type Arylation in Action... 

Scheme 7.42 Electrophilic C—H bond activation or transmetallation as an entry into oxidative Mizoroki-Heck-type arylations.

Fallacious acetate j trie thy lamine (Z)-p-Silylstyrenes from ar. iodides Heck-type arylation with addition of two C-atoms... 

An interesting palladium-catalysed oxidative arylalkylation of aromatic acrylamides (282) with MeCN that proceeds through a dual C-H bond cleavage of both arene and acetonitrile and affords indolinones (283) has been reported. Mechanistic studies revealed a fast Heck-type arylation of the C=C bond and a rate-limiting C-H activation of the acetonitrile. The initial palladation of the aromatic moiety apparently proceeds with the assistance of the amide group. ... 

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