Heck-type phenylation

Scheme 2 Heck-type phenylation reaction of styrene with Ph3Bi ...

Scheme 5 Heck-type phenylation reaction with organobismuth compounds...

Scheme 8 Heck-type phenylation reaction of allyl alcohol with Ph2BiCl...

Heck-type phenylation of allyl alcohol with Ph2BiCl proceeded in the presence of Pd(OAc)2 to afford an isomerized product, 3-phenylpropanal, in 61% yield together with biphenyl (Scheme 8) [23]. The reaction required air (or oxygen) for catalytic conversion. A similar reaction with Ph2SbCl was more efficient and afforded 3-phenylpropanal in 94% yield. 

The rate of the palladium-catalysed Heck-type phenylation of allylic alcohols has been found to be markedly enhanced by addition of tertiary amines454. Regioselectivity can be increased, in some cases, by adding E NCl or employing a Wilkinson Rh catalyst (rather than pd)455 456. Another Heck-type reaction involves addition of arenediazonium tetraflu-oroborates to a-silylstyrenes to give (Z )-PhCH=CHAr. A BF4 -mediated vyw-elimination of silicon and palladium has been suggested to account for the stereochemistry457. 

A drawback of the Heck-type reaction is that it is not strictly regioselective [119]. Depending on the substituents >1% of 1,1-diarylation is observed. Soluble 2,5-dialkoxy-PPVs 63 or 2-phenyl-PPV PPPV 93, without 1,1-diarylated moieties, were synthesized by Heitz et al. in a Suzuki-type cross coupling of substituted 1,4-phenylenediboronic acids and fran5-l,2-dibromoethylene, catalyzed by Pd(0) compounds [120]. However, about 3% of biaryl defect structures are observed in the coupling products (M up to 12,000), resulting from homocoupling of boronic acid functions. 

Further investigations by Jeffery indicated the rate- and selectivity-enhancing ability of tetraalkylammonium salts in Heck-type reactions [7]. In particular, tetra-butylammonium chloride, bromide and hydrogensulfate are extensively applied in aqueous DMF and acetonitrile, resulting in the fast and clean conversion of phenyl iodide with acrylic acid in 96% yield. 

Catellani and Lautens have independently reported unique palladium/ norbornene-catalyzed reactions of aryl halides, which mechanistically involve a reversible alkene insertion/p-carbon elimination process [11]. For example, iodobenzene reacted with 1-iodobutane and methyl acrylate to form the multiply-alkylated benzene 29 (Scheme 7.9) [12]. The following mechanism is proposed oxidative addition of phenyl iodide onto palladium generates phenylpalladium(ll) iodide. A double bond of norbornene inserts into the C-Pd bond to form an alkylpalladium species, which cleaves a C-H bond nearby to form the palladacycle 25. -Butyl iodide then reacts with 25 to form the Pd(IV) intermediate 26, which undergoes reductive elimination. Repetition of the cyclometalation/alkylation process leads to the formation of 27. Then, P-carbon elimination affords the arylpalladium species 28 together with norbornene. Subsequently, a Heck-type reaction takes place with methyl acrylate, giving rise to 29. 

Heck-type Palladium-catalyzed Phenylation of Alkenes. 

Upon exposure to Heck-type reaction conditions, a triquinacene derivative was shown to react with iodobenzene in a process that led to the introduction of a phenyl group at the central (and sp -hybridized) carbon of the tricyclic ring system (eq 125). ... 

In 1999, Mikami s group reported the first example of an intermolecular asymmetric Fujiwara-Moritani reaction of benzene with cyclic alkenes using a Pd catalyst co-ordinating to a chiral sulfonylamide-oxazoline ligand (Scheme 7.24). With PhCOs Bu as the oxidant, the coupling reaction occurred with moderate enantioselectivity (up to 49% ee), although the chemical yield was low. The reaction is considered to involve the formation of a phenyl-Pd species via electrophilic C-H substitution by Pd(ii), and Heck-type cyclization followed by re-oxidation of the resultant Pd(0) species. 

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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