Heck reaction alkenyl chlorides

The Heck reaction can be used to couple alkenyl, aryl, allyl (the intramolecular Heck reaction on aUyUc substrates is called a palladaene reaction),f ° t f benzyl, methyl, alkoxycarbonyhnethyl, alkynyl, certain alkyl, and silyl fragments to a variety of alkenes. The nature of the leaving group greatly affects the reaction rate aryl iodides react faster than bromides, and aryl chlorides are notoriously unreactive unless special catalysts or ligands and elevated temperatures are used to enhance the reaction rate. This has been taken to indicate that the oxidative addition of the haloarene (haloalkene) to pal-ladium(O) is the rate-determining step. " It has been shown that the Heck reaction can be performed with aryldiazonium salts, A -nitroso-Af-arylacetamides, and hy-pervalent iodo compounds " at room temperature. 

Compared with palladium-catalysed Heck reactions, the studies of nickel-catalysed Heck reactions are far fewer. Theoretical studies show that oxidative addition and olefin insertion occur easier in the nickel system than in the palladium system. On the other hand, p-hydride elimination and catalyst regeneration through HX removal are more difficult in a nickel-based catalytic system." The former characters may make the nickel-catalysed Heck reaction of alkenyl or aryl chloride proceed relatively easily and the latter... 

Cobalt-catalysed electrochemical arylation reactions of acrylates were achieved by Gosmini and coworkers. The presence of 2,2 -bipyridine (Bpy, 63) was found crucial to reduce the formation of conjugate addition products in this transformation. Notably, this Mizoroki-Heck-type reaction proved applicable to aryl iodides and bromides and to an alkenyl chloride (Scheme 10.22) [48]. 

This type of cyclization reaction was applied in the synthesis of p-carbo-linones and total synthesis of dipyrrolobenzoquinone ( )-terreusinone as well. In 2005, Barluenga and co-workers reported a novel approach for the synthesis of indoles from o-bromoanilines and alkenyl halides via a palladium-catalyzed cascade process (Scheme 2.112). The reaction involves an alkenyl amination followed by an intramolecular Heck reaction. As the authors demonstrated, this process represents the first example of the participation of alkenyl amination reactions in Pd-catalyzed cascade reactions. Initially, the relative reactivity of aiyl and alkenyl bromides and chlorides towards Pd-catalyzed amination was investigated. Competition... 

As will be discussed later in this chapter (Section E, 7), vinyl iodides such as (E)-l-iodopentene (Scheme 7.6c) also react with alkenyl boron reagents (Chapter 6, Scheme 6.26) in a palladium-catalyzed process. The Suzuki reaction (ct the Heck reaction, Chapter 6, Scheme 6.54 and footnote page 371) also results in the formation of a new carbon-carbon bond (Scheme 7.6c), and, generally, the iodides are more reactive than the bromides, and they, in turn, are more reactive than the vinyl chlorides. 

Cross-coupling Reactions. The allylpalladium chloride dimer (1) has served as an excellent active catalyst precursor for various cross-coupling reactions. The well-known Mizoroki-Heck reaction was widely exemplified in the presence of the system (1)/-Tedicyp (eq 77). Several aryl bromides were reacted with aryl acrylates, styrenyl or alkenyl derivatives, ethyleneglycol vinyl ether, and alk-l-en-3-ol. 8 This catalytic system was efficient for the coupling of vinyl bromides as well. The catalyst loading can be reduced and the substrate/catalyst ratio could reach 100 000 000 in some cases. 

Accordingly, catalytic and stoichiometric amounts of cuprous salts were employed for Mizoroki-Heck-type reactions of various conjugated alkenes [ 19]. Intermolecular catalytic arylations of methyl acrylate (1, not shown) and styrene (2) were accomplished under ligand-free conditions using CuBr (3) or Cul (4) as catalyst in A-methyl-2-pyrrolidinone (NMP) as solvent various aryl iodides could be employed (Scheme 10.2). On the contrary, aryl bromides and chlorides, as well as aliphatic halides, were found to be unsuitable substrates. The reactions employing an alkenyl bromide, methylmethacrolein or methyl methacrylate required stoichiometric amounts of copper salts. 

In addition to the cross-coupling reactions of alkyl halides or sulfonates with organometallic nucleophiles, the former can also directly undergo C-C bond formation with nonactivated C-H bonds of alkenes or arenes in a Heck-type reaction. Iron-catalyzed intramolecular dehydrohalogenation of 2-iodoethanal alkenyl acetals with phenyl-magnesium bromide in the presence of a catalytic amount of iron(II) chloride provides tetrahydrofliran derivatives in moderate yields (Scheme 4-240). Allyl 2-halophenyl ethers provide dihydrobenzofiiran derivatives under these conditions. ... 

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