Phosphines Stille coupling

Collum129 reported that while the Stille coupling can proceed without using a phosphine ligand, the addition of a water-soluble ligand improved the yield of the reaction. Water-soluble aryl and vinyl halides were coupled with alkyl-, aryl-, and vinyltrichlorostannane derivatives in this way (Eq. 6.39). 

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 1998, Yamamoto et al. reported the first catalytic enantioselective allylation of imines with allyltributylstannane in the presence of a chiral 7i-allylpalladium complex 23 (Scheme 9) [15]. The imines derived from aromatic aldehydes underwent the allylation with high ee values. Unfortunately, the allylation reaction of aliphatic imines resulted in modest enantioselectivities. They proposed that a bis-Jt-allylpalladium complex is a reactive intermediate for the allylation and reacts with imines as a nucleophile. The bis-Jt-allylpalladium complex seemed the most likely candidate for the Stille coupling [16]. Indeed, the Stille coupling reaction takes place in the presence of triphenylphosphine even if imines are present, whereas the allylation of imines occurs in the absence of the phosphine [17]. They suggested the phosphine ligand played a key role in controlling the... 

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)... 

The reactions have a very wide scope. Acyl halides serve as substrates for Stille couplings in addition to the usual aryl and alkenyl halides however, most alkyl halides cannot be used as substrates. Like Pd-catalyzed carbonylations, reactions proceed most quickly when X = I and rather slowly when X = Cl, although especially bulky phosphine ligands such as /-Bu3P allow even aryl chlorides to undergo coupling at room temperature. Again, triflates are also widely... 

The ortho-palladated phosphinite-phosphine complexes shown in equation 45 are active for Suzuki and Stille coupling of aryl chlorides152,153. Hence, Bedford and coworkers studied the activity of these complexes for the animation of aryl chlorides151. 

An air and moisture stable, low-coordinate phosphine ligand has been found to be effective in the Stille coupling of pyridine derivatives. This was exemplified in the transformation of 136 to 169 [85]. 

The Stille coupling of 4-bromomethyloxazole 56 with vinyltributyltin in the presence of Pd2(dba)3 and tri(2-fuiyl)phosphine produced 4-allyloxazole 57 in 82% yield [7]. Allyloxazole 57 is a key intermediate in the synthesis of leucascandrohde A. 

In this manner, unprotected nucleosides can be coupled to boronic acids in moderate yields. In the Stille coupling reaction, the palladium catalyst formed in situ from PdCl2 and four equivalents of TPPMS was used effectively to couple various aryl halides with R groups on RSnCl3 (Eq. 3) [16]. The use of this catalyst improved the yield and reproducibility compared to the use of PdCl2 alone. The So-nogashira coupling of alkynes with aryl halides is an additional route for the formation of sp—sp2 bonds. The use of this water-soluble phosphine with Pd(OAc)2... 

Carbonylative intramolecular Stille coupling to form macrocyclic molecules was investigated with a palladium complex of the polymer-bound ferrocenyl phosphine 21. One of the major problems encountered in the intramolecular... 

The mechanism follows that of a normal Stille coupling except that the carbon monoxide first exchanges for one of the phosphine ligands and then very rapidly inserts to produce an acyl palladium(II) complex. Transmetallation with the vinyl stannane in the usual way forms trimethylstannyl iodide and the key palladium complex carrying two carbon ligands. Transmetallation is always the slow step in these coupling reactions, allowing time for the carbon monoxide insertion. The final step—reductive elimination—releases the Pd(0) catalyst for the next cycle. 

Although the active participation of Pd(IV) intermediates in catalysis is currently well established [21, 22], it has been shown that the catalytic activity of paUadacycles is usually due to Pd nanoparticles or soluble Pd(0) species arising from partial or complete decomposition processes. Hartwig and Louie [23] showed that paUadacycles of type 1 are reduced by amines (in aryl amination reactions) or stan-nanes (in the Stille coupling) to afford Pd(0) phosphine complexes. Furthermore,... 

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