Iodoarenes olefination

Bimetallic Pd/Ni [121] andPd/Co [122] systems have exhibited considerable catalytic activity in the Heck reaction of nonactivated chloroarenes with ethyl acrylate, acrylonitrile, and acrylic acid. For instance, ethyl acrylate and acrylonitrile reacted smoothly with chlorobenzene in the presence of Nal and catalytic amounts of NiBr2, Pd2(dba)3, and o-Tol3P in DMF to give E-isomers of ethyl cinnamate and cinnamonitrile, respectively [121]. The reaction occurred via the nickel-catalyzed halogen exchange between ArCl and Nal, followed by the conventional palladium-catalyzed olefination of the iodoarene generated in situ. 

In this context, a functionalized ionic liquid, 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate [hemim][BF4], is reported as an efficient and recyclable reaction medium for the palladium catalyzed Heck reaction. The olefination of iodoarenes and bromoarenes with olefins generates the corresponding products in good to excellent yields under phosphine-ffee reaction conditions. After separation of the product, fresh starting materials are charged into the recovered ionic liquid which entraps the palladium catalyst. The reactions still proceed quantitatively for six cycles, without significant loss of catalytic activity. " The effect of both the cation and the anion on the chemical yield is shown in Figure 28. 

If water-soluble phosphine ligands are applied, extremely mild reaction conditions can be achieved. Especially, Pd(TPPMS)3, which converts 4-iodotoluene, is tolerant of a broad range of functional groups, including those present in unprotected nucleotides and amino acids [6]. Interestingly, even the coupling of a donor-substituted iodoarenes and cyclic olefins can be conducted by palladium acetate with TPPTS at only 25 °C in aqueous acetonitrile. However, the low rates observed require a reaction time of up to 48 h for high conversions [12]. 

A variety of olefin metatheses were carried out by sol-gel entrapped Grubbs catalysts (e.g.. Scheme 24-21) (Kingsbury, 2001). Heck coupling of bromo- and iodoarenes with various alkenes by (physically) entrapped PdCl2(PPh3)2 has recently been carried out (Scheme 24-22). ... 

In 2001, Mauleon et al. reported an unusual palladium-cascade arylation of a,P-unsaturated phenyl sulfones 23 under Heck reaction conditions [12]. Contrary to the work of Fuchs and others [13], Mauledn et al. described the intermolecular reaction of a,P-unsaturated sulfones with a large excess of iodobenzene (or / -substituted iodoarenes) in the presence of Ag COj as base, which occurred mainly through a complex cascade reaction in which three molecules of iodobenzene and one molecule of vinyl sulfone were involved, forming fused polycyclic compounds 25 rather than the Heck trisubstituted olefin expected. The authors propose a mechanism involving Heck reaction and C-H activation pathways (Scheme 6.5). 

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