Transition Sonogashira reaction

For the further decoration of the pyrazinone scaffold via transition metal-catalyzed chemistry, the Sonogashira reaction [45-50] has also been investigated on the C-3 position of the pyrazinone, applying microwave irradiation conditions (Scheme 17) [29]. It was found that microwave irradiation at 120 °C for 15 min of a mixture of the starting material, Pd(OAc)2, Cul and PPha in TEA/DMF were the appropriate reaction conditions. 

The Sonogashira reaction is a transition metal-catalyzed coupling reaction which is widely used for the preparation of alkyl-, aryl- and diaryl-substituted acetylenes (Table 4.7) [120]. This reaction is a key step in natural product synthesis and is also applied in optical and electronic applications. Sonogashira reactions involve the use of an organic solvent with a stoichiometric portion of a base for capturing the... 

Transition metal-catalyzed transformations are of major importance in synthetic organic chemistry [1], This reflects also the increasing number of domino processes starting with such a reaction. In particular, Pd-catalyzed domino transformations have seen an astounding development over the past years with the Heck reaction [2] - the Pd-catalyzed transformation of aryl halides or triflates as well as of alkenyl halides or triflates with alkenes or alkynes - being used most often. This has been combined with another Heck reaction or a cross-coupling reaction [3] such as Suzuki, Stille, and Sonogashira reactions. Moreover, several examples have been published with a Tsuji-Trost reaction [lb, 4], a carbonylation, a pericyclic or an aldol reaction as the second step. 

Domino transition metal-catalyzed processes can also start with a cross-coupling reaction most often, Suzuki, Stille and Sonogashira reactions are used in this context They can be combined with another Pd-catalyzed transformation, and a number of examples have also been reported where a pericydic reaction, usually a Diels-Alder reaction, follows. An interesting combination is also a Pd-catalyzed borina-tion followed by a Suzuki reaction. 

However, the real breakthrough in this area is due to the development of catalysis by transition metals, with the Heck, Suzuki, Sonogashira reactions and other related coupling process. ... 

The possibility of performing Sonogashira reactions without use of transition metals is undoubtedly very appealing. By using microwaves Erik Van der Eycken and his group were able to couple phenyl acetylene with different aryl halides at 175 °C using sodium carbonate and tetrabutylammonium bromide in water [lOOj. Reaction times varied from 5 to 25 min usually with good to excellent yields. The... 

Choudhary BM, Madhi S, Chowdari NS, Kantam ML, Sreedhar B (2002) Copper-free Sonogashira reaction with transition-metal nanoparticles. J Am Chem Soc 124 14127... 

In domino transition-metal-catalysed processes, cross-coupling reactions can also be nsed as the starting transformation. Most often, Suzuki, Stille and Sonogashira reactions are employed in this context. They can be combined with a Mizoroki-Heck reaction and other palladium-catalysed transformations. 

Using transition-metal catalysts for C-C bond forming at carbons bearing acidic protons, such as the position a- to a carbonyl group is discussed in Section 2.11, as the C-H bond is activated by its position, and not primarily by the metal. The coupling of terminal alkynes, the Sonogashira reaction, is also discussed in Section 2.8. The use of carbene and nitrene complexes for bond formation through C-H activation is a well-established process. This is discussed in Section 8.5.2. 

In terms of synthetic planning, it must be noted that a transition-metal catalyst is not required for this cyclization. o-Alkynylamines can be cyclized to indoles under basic conditions, especially if the nitrogen atom has an electron-withdrawing substituent to lower the pKa. Just such a base-catalysed cyclization was employed in a synthesis of goniomitine (Scheme 6.20), after a Sonogashira reaction was employed to synthesize the substrate. Similarly, benzofurans are easily prepared by base catalysed cyclization as in a synthesis of Ailanthoidol (Scheme 2.115). The transition-metal catalysed cyclization is of particular importance when... 

Some drawbacks of the precursor routes mentioned above have been overcome by the use of polycondensation- and C-C-bond-coupling reactions. To produce soluble PPV-, poly(thiophene)-, or poly(pyrrol) derivatives for spin coating preparation, various types of transition metal catalyzed reactions, such as the Heck-, Suzuki-, and Sonogashira-reaction, Wittig- and Wittig-Horner-type coupling reactions, or the McMurry- and Knoevenagel-condensation have been utilized. 

Three additional processes, the Stille, Suzuki, and Sonogashira reactions, further broaden the scope of transition metal-catalyzed bond-forming processes. All utilize catalytic palladium or nickel the differences lie... 

Singh B.K., Kaval N., Tomar S., Van der Eycken E., Parmar VS. Transition metal-catalyzed carbon-carbon bond formation Suzuki, Heck, and Sonogashira reactions using micro-wave and microtechnology. Org. Process Res. Dev. 2008 12 (3) 468 74. 

Silylene-based pincer ligands offer exciting reactivities in terms of transition metal complex formation and their applications in catalytic systems. The pincer complex [SiCSi)Ni(II) can be synthesized by oxidative addition of C—H bond of the corresponding [SiC(H)Si] ligand. [SiCSi]Ni(II) complex has been employed as catalyst for Ni-catalyzed Sonogashira reactions (8). Moreover bis(silylene) pincer complexes of iridium and rhodium reveal strong 5-donating ability of divalent silicon and have demonstrated selectivity in catalytic C—H borylation reactions with arenes (9). 

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