Heck coupling phenyl-substituted

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. 

Coupling of 1 with iodobenzene under Heck reaction conditions gave the phenyl-substituted diene 242-Ph which was isolated in up to 78% yield [146-148]. When heated at 80 °C in DMF or MeCN with various dienophiles 244-R (acrylate, maleate, or fumarate), 242-Ph and its analogs 242-Ar obtained from 1 and other haloarenes cleanly gave the spiro[2.5]octene derivatives 245-Ar (Scheme 57). 

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-substituted PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and feA-boronic acid 30. Its absorption (2max = 385 nm) and emission (/li ax=475 nm) maxima were strongly... 

In such a situation, but without an additional substituent on the Pd-substituted cyclopropane ring, the reaction mode along pathway B normally predominates. This is illustrated by the Heck coupling reaction of bicyclopropylidene (50) with iodobenzene, which under normal Heck conditions gave the phenyl-substituted diene 78 in up to 78% isolated yield or, in the presence of a dienophUe, the corresponding Diels-Alder product in excellent yield (see Sects. IV.2.2.1, IV.2.1.2, and The coupling of 50 with iodobenzene in... 

Ternary Pd-catalyzed coupling reactions of bicyclic olefins (most often norbor-nadiene is used) with aryl and vinyl halides and various nucleophiles have been investigated intensively over the past few years [44]. A new approach in this field is to combine Heck and Suzuki reactions using a mixture of phenyliodide, phenyl-boronic acid and the norbornadiene dicarboxylate. Optimizing the conditions led to 84% of the desired biphenylnorbornene dicarboxylate [45]. Substituted phenyl-iodides and phenylboronic acids can also be used, though the variation at the norbornadiene moiety is highly limited. 

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. 

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