Solvents Stille coupling

Stille coupling involves the use of tin reactants. Tin is both toxic and difficult to remove. In an elegant extension of the pioneering work of Horvath [59], Curran and his coworkers prepared fluorous tin reactants that facilitated Stille reactions and enabled the convenient isolation and separation of products afterwards [60], Probably owing to low solubility of fluorine-containing compounds in organic solvents, the reactions normally required about one day at 80 °C. With microwave heating, they were completed within minutes [61]. 

The efficiency of fluorous Stille coupling reactions [5 a] is enhanced by use of microwave irradiation (Scheme 8.2). The reaction proceeds in 79% yield after 2 min with DMF as the microwave-active solvent. 

The fluorous Stille procedure has also been applied to a one-pot hydrostannylation of an acetylenic compound in the hybrid fluorous/organic solvent benzotrifluoride (BTF). Subsequent Stille coupling of the product in BTF/DM F, as shown in Eq. (11.32), was easily achieved in 8 min with 60 W single-mode microwave irradiation [43],... 

The palladium-catalyzed coupling of aiyl and vinyl halides to organotin compounds, known as Stille coupling, is one of the most important catalytic methods of carbon-carbon bond formation. The reaction is generally conducted in polar organic solvents, such as dimethylformamide, with tertiary phosphine complexes of palladium, although phosphine-free complexes or simple Pd-salts are also frequently used as catalysts [8]. 

In addition to all the good features of the Stille couplings, there are a few problems with the use of RSnMles or RSn(n-Bu)3 in aqueous solutions. These compounds are rather volatile and water-insoluble but this can be overcome with the aid of co-solvents. However, the products of the reaction still contain alkyltin species which are toxic and environmentally unacceptable. Furthermore, only one of the four Sn-C units take active part in the... 

The Stille coupling reaction has been performed in l-bntyl-3-methylimidazolium tetrafluoroborate. Use of this solvent system allows for facile recycling of the solvent and catalyst system, which can be used at least five times with little loss in activity. An interesting preference in starting catalyst oxidation state for nse with aryl bromides and aryl iodides was observed (Handy and Zhang, 2001). 

Stille coupling of phenyl iodide with vinyl tin reagents Pd2(dba)3/tris[3,5- bis(trifluoromethyl)phenyl]-phosphine Solvent replacement Morita et al. (1998)... 

Figure 6.6 Cyclic (left) and open (right) transition states proposed in the Stille coupling reaction S = solvent (or ligand)...

Finally, a new effect of the addition of copper salts was noted recently. The regioselectivity of the Stille coupling of 3,5-dibromo-2-pyrone can be modified in the presence of Cul in DMF as the solvent, leading to the products shown in Scheme 5.3.5. ... 

Stille coupling reactions of organic triflates are often facilitated by added LiCl when conducted in THF solvent. Presumably the chloride anion replaces the triflate ligand on palladium following oxidative addition, which leads to increased stability of the Pd(Ar)(X) species [35] this additive may also assist in the transmetalation step. However, LiCl is not needed when the StiUe reactions are carried out in polar solvents like NMP [36]. 

Heck and Stille coupling reactions, also allowing reactions to be conducted under solvent-free conditions. The synergic effect of polymer 96 and TSIL not only reflected an increased stability during storage but also an enhanced activity during catalysis. Scheme 1.62 shows a typical Suzuki reaction occurring in an aqueous biphasic medium. 

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