Sonogashira cross-coupling conditions

A similar approach was used by Knochel and coworkers for the first synthesis of unsubstituted b-SFs-indole (7) (12CEJ10234). They directly used unprotected 2-bromo-5-SF5-aniline (8) in reaction with trimethylsilylacetylene under Sonogashira cross-coupling conditions, which provided SFs-substituted 2-ethynyl(trimethylsilyl)aniline (9). Subsequent cychzation using KH in 1-methyl-2-pyrrolidinone afforded the b-SFs-indole (7) in 83% yield (Scheme 3). 

Marsella and coworkers exploited perfluorophenyl-phenyl quadrupole interactions to template the synthesis of a thiophene-containing cyclophane [44]. As shown in Scheme 6.14, when the oligomeric precursors 98-101 were treated with Sonogashira cross-coupling conditions, the mixed perfluorophenyl-phenyl cyclophane 102 was reproducibly achieved in greater yield than either of the symmetrical analogs 103 and 104. Other mixed macrocyclic derivatives were also prepared as part of this study, and their findings with these model systems supported... 

Two possible approaches were shown for the Sonogashira cross-coupling/ benzannulation of enyne with diyne cascade transformation (Scheme 14.19) [11a]. Accordingly, three-component coupling between dihalide 41 and two molecules of terminal diyne produced phenanthren-9(10//)-one derivatives 43 with modest yields under Sonogashira cross-coupling conditions (path A). Incorporation of two different substituents to the final product 46 was achieved via a stepwise addition of terminal alkynes (path B). 

A palladium catalyst with a less electron-rich ligand, 2,2-dipyridyl-methylamine-based palladium complexes (4.2), is effective for coupling of aryl iodides or bromides with terminal alkynes in the presence of pyrrolidine and tetrabutylammonium acetate (TBAB) at 100°C in water.37 However, the reactions were shown to be faster in NMP solvent than in water under the reaction conditions. Palladium-phosphinous acid (POPd) was also reported as an effective catalyst for the Sonogashira cross-coupling reaction of aryl alkynes with aryl iodides, bromides, or chlorides in water (Eq. 4.18).38... 

A recent publication by the group of Barbarella has disclosed the rapid preparation of poorly soluble unsubstituted and modified a-quinque- and sexithiophenes by the extensive use of bromination/iodination steps and microwave-assisted Suzuki and Sonogashira cross-couplings (Scheme 6.16) [42]. Suzuki reactions were either carried out under solvent-free conditions on a strongly basic potassium fluoride/ alumina support for the synthesis of soluble oligothiophenes, or in solution phase for the preparation of the rather insoluble a-quinque- and sexithiophenes. In both cases, 5 mol% of [l,l -bis(diphenylphosphino)ferrocene]dichloropalladium(II)... 

Dibowski, H., Schmidtchen, F. P. Sonogashira cross-couplings using biocompatible conditions in water. Tetrahedron Lett. 1998, 39, 525-528. 

Sometimes organoboranes or stannanes are either unavailable or too unstable under Suzuki or Stille cross-coupling conditions. The Sonogashira reaction, however, does not involve the synthesis or handling of stoichiometric amounts of M -R... 

The same researchers reported that a 2-hydroxymethyl protecting group (208) is compatible with Sonogashira cross-coupling reaction conditions [76, 89]. Remarkably, using this protective group, alkynylation occurs first followed immediately by the loss of formaldehyde (deprotection) via a base or heat promoted retro-ene reaction. 

Type of reaction C-C bond formation Reaction condition solvent-free Keywords Sonogashira cross-coupling, alkyne... 

Type of reaction C-C bond formatitMi Reaction conditions Dioxane, room temperature Synthetic strategy Aiyl bromide - alkyne Sonogashira cross-coupling Catalyst Pd(PhCN)2Cl2 / P(t-Bu>3... 

The preparation of (alk-l-ynyl)thiophenes 154 is possible via palladium-catalyzed Sonogashira cross-coupling reactions between iodo- or bromothiophenes 152 and terminal alkynes 153 (Scheme 60, Table 38) [309, 360, 363, 364], Alkynylated thiophenes represent an important structural motif found in many ir-electronic systems such as molecular rods or conjugated macrocycles [163, 362, 365, 366], In the case of bromoiodo-substituted thiophenes, the more reactive iodine atom is replaced selectively [367]. Some coupling methods require stoichiometric amotmts of paUadium(0) [360, 368], whereas other methods proceed successfully tmder photochemical conditions without the need of a catalyst [369]. Recent... 

Recently it has been observed that NCBs have been used as a support for heterogeneous catalyst due to its hollow core, mesoporous and ball-like structure. Park et al. [70] developed Pd(OAC)2 catalyst supported on NCBs and applied it for the synthesis of 2-substituted benzofuran from u-iodo phenol and various substituted terminal alkynes using Sonogashira cross-coupling reaction under copper and ligand-free condition. 

Analogous intermolecular one-pot cascade transformation has been developed by Xi et al. [11b]. Consequently, a-bromoacrylates reacted with terminal acetylenes with the formation of densely substituted styrenes in a single transformation under Sonogashira cross-coupling reaction conditions (Scheme 14.14). This method was efficient for both aryl or alkyl acetylenes. Among vinyl bromides, only acrylate derivatives were shown to produce styrene derivatives in good yields. 

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