Heck-type oxidative alkenylation

Ruthenium(O) complexes such as Ru(COD)(COT) catalyze the dehydrohalo-genative coupling of vinyl halides with olefins to give substituted conjugated dienes in a Heck-type reaction [11]. Thus, alkenyl halides readily react with activated olefins to produce dienes 16 (Eq. 7). Oxidative addition of vinyl halide, followed by regioselective insertion of an electron-deficient olefin and by -hydrogen elimination leads to the diene. 

Oxidative addition of the carbon-halogen bond is a well-documented reaction for Group 10 transition metal complexes, but it is relatively limited for ruthenium. The example given here involves the reversible oxidative addition of allyl halide to RuCp(CO)2X to produce RuCp(p -allyl)X2 [78]. Oxidative addition of allyl halide to a Ru(0) complex Ru(l,5-COD)(l,3,5-COT) is also reported, but the product yield was poor [79]. Nevertheless, a catalytic Heck-type alkenylation of bromostyrene with methyl acrylate by Ru(l,5-COD)(l,3,5-COT) proceeded smoothly [80]. A cross-coupling reaction of alkenyl halide with Grignard reagents or alkyl lithium also pro-... 

Palladium chemistry has been utilised to introduce aryl groups to a furan a-position by substitution of hydrogen, and via boronic acids, and in Heck-type alkenylations, again at C-2, via oxidative type palladation (cf. section 2.7.2.1). 

Herein, a survey of the literature up to mid 2007 is provided, covering catalytic arylation and alkenylation reactions of alkenes with metals other than palladium. The review summarizes Mizoroki-Heck-type reactions employing organic (pseudo)halides as electrophiles (Scheme 10.1), while oxidative Mizoroki-Heck-type reactions [6] are beyond the scope of this review (Chapters 4 and 9). Valuable transition-metal-catalysed arylation reactions of alkenes employing stoichiometric amounts of organometallic compounds as... 

Oxidations. Cu(OAc)2 has been used as a reoxidant in Pd catalyzed reactions of aryl and alkenyl boronic acids with alkenes and alkynes, and aryltins, and aryl or alkenyl silanols with electron deficient olefins (eq 26). This Mizoroki-Heck type reaction supposedly proceeds through a Pd(II)-boron transmetallation step, followed by addition across the double (triple) bond and final... 

Another important type of reactivity of palladium, namely oxidative addition to Pd(0), is the foundation for several methods of forming carbon-carbon bonds. Aryl126 and alkenyl127 halides react with alkenes in the presence of catalytic amounts of palladium to give net substitution of the halide by the alkenyl group. The reaction, known as the Heck reaction,128 is quite general and has been observed for simple alkenes, aryl-substituted alkenes, and substituted alkenes such as acrylate esters, vinyl ethers, and A-vinylamides.129... 

The Pd(0)-catalyzed reactions of propargylic compounds so far discovered can be classified into four types, I, II, III, and TV, from a mechanistic viewpoint. The allenyl intermediate complex 8 undergoes three types of transformation, depending on reactants. The reactions of Type I proceed by insertion of unsaturated bonds into the a-bond between palladium and sp carbon in 8. This a-bond has a reactivity similar to the a-bond formed by the oxidative addition of alkenyl halides to Pd(0) in the Heck reaction [3]. Therefore, reactions similar to those observed in the Heck reaction are expected to occur witli the intermediate 8. Alkenes and carbon monoxide are known to insert into the palladium-carbon a-bond. The allene derivatives 9 are formed by these reactions (Scheme 11.3). 

Ru complexes catalyze the reaction between 2-aryl pyridines and alkenyl esters (Scheme 23.16) [75]. These types of olefins are often only slowly reacting substrates in oxidative Heck (Fujiwara-Moritani) reactions [18] thus, their use in Ru-catalyzed C-H olefinations is a remarkable advance. The shown reaction is overall redox neutral and produces 1 equivalent of alcohol or acid as side product. A variety of heterocyclic directing groups can be employed, and many functional groups are tolerated. However, the olefin scope of the reaction is somewhat limited to alkyl- and aryl-substituted alkenes. 

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