Sonogashira-type cross-coupling

Substituted propargylic carbonates react with terminal acetylenes in the presence of a catalytic amount of Pd(PPh3)4 and Cul to produce Sonogashira-type cross-coupling products (Eq. 9.114) [84]. Presumably, the reaction proceeds through an allenylpalladium complex. Addition of a salt, such as KBr, increased the yield of the coupling product. Only tetrasubstituted allenes could be obtained by this procedure. 

A Pd(II)- and Ni(II)-catalysed Sonogashira-type cross-coupling of vinyl tellurides and vinyl tellurium dichlorides with terminal alkynes... 

Fig. 12.8 Synthetic semi-automated solid-phase strategy for the modification of DNA bases by chromophores via an acetylene bridge and Sonogashira-type cross-couplings.

In an effort to overcome steric interactions due to -substituents in cyclotetra(2,3-thienylene)s 4.6 (see above), Marsella et al. synthesized expanded thiophene-fused didehydro [12]annulene 4.32, which incorporated two additional ethynylene groups between the -positions of the cycUc stmcture (Scheme 1.44) [408]. Regiospeciflc halogenation of a 2,2 -bithiophene and Sonogashira-type cross-coupling with the ethynylated counter part were key elements of the synthetic strategy, which was also used to prepare a further extended macrocycle 4.33 (Chart 1.54), profiting from quadrupolar interactions of the central phenylene units [409]. 

Sonogashira-type cross-coupling of 103 failed and could only be performed on exchange of the bromo substituents by more reactive iodo functionalities. 

Utesch, N. F., Diederich, F. Acetylenic scaffolding on solid support Poly(triacetylene)-derived oligomers by Sonogashira and Cadiot-Chodkiewicz-type cross-coupling reactions. Org. Biomol. Chem. 2003,1, 237-239. 

C. POLYCONDENSATIONS USING HECK-, STILLE-, AND SONOGASHIRA/IIAGIHARA-TYPE CROSS-COUPLING REACTIONS... 

Palladium-catalyzed cross-coupling is a powerful tool for the synthesis of various 7c-conjugated molecules and polymers through sp and sp carbon-carbon bond formation [17-20]. Scheme 3 shows the synthetic routes for poly (p-arylene-ethynylene)-type (PAE-type) jc-stacked polymers by Sonogashira-Hagihara cross-coupling [21, 22]. Polymer 13 was obtained from the monomers pseudo-para-dibromo[2.2]... 

Carbon-carbon bond formation reactions and the CH activation of methane are another example where NHC complexes have been used successfully in catalytic applications. Palladium-catalysed reactions include Heck-type reactions, especially the Mizoroki-Heck reaction itself [171-175], and various cross-coupling reactions [176-182]. They have also been found useful for related reactions like the Sonogashira coupling [183-185] or the Buchwald-Hartwig amination [186-189]. The reactions are similar concerning the first step of the catalytic cycle, the oxidative addition of aryl halides to palladium(O) species. This is facilitated by electron-donating substituents and therefore the development of highly active catalysts has focussed on NHC complexes. 

Other successful examples of catalysts containing NHC ligands are found in palladium- and nickel-catalyzed carbon-carbon bond formations. The catalyst development with these metals has focused in particular on Heck-type reactions, especially the Mizoroki-Heck reaction itself [Eq. (42)] and various cross coupling reactions [Eq. (43)], e.g., the Suzuki-Miyaura reaction ([M] = and the Kumada-Corriu reaction ([M] = MgBr). " Related reactions like the Sonogashira coupling [Eq. (44)]326-329 Buchwald-... 

As shown in Equation (37), 4,5-dibromo-2-furaldehyde and methyl 4,5-dibromo-2-furoate underwent regioselective cross-coupling reaction at the 5-position with alkynes under Sonogashira-type conditions, presumably due to the activation of the 5-position by the electron-withdrawing groups at the 2-position toward oxidative palladium insertion <1998TL1729, 1999EJO2045>. 

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