Ligand triphenylarsine

The Stille coupling of 2-chloro-5-tributylstannylpyridine with an enantiopure 2-iodo-cyclohexenon (7.29.) derivative formed the basis of the total synthesis of (+)-epibatidine. The reaction is a nice example of the chemical inertness of arylstannanes and the mildness of the coupling conditions. Both the enone moiety and the chiral ally lie centre remained untouched in the process. The effective coupling required the use of a soft ligand, triphenylarsine and the addition of copper(I) iodide as co-catalyst.40... 

FIGURE 9.4 Influence of large ligands such as triphenylarsine on the bonding mode of SCN. ... 

The Stille coupling of a-iodo enones is sluggish under standard conditions. Significant rate enhancement was observed for the Stille reaction of 2-chloro-5-tributylstannylpyridine and a-iodo enone 76 using triphenylarsine as the soft palladium ligand and Cul as the co-catalyst [63], Oxygenated functionalities did not affect the efficiency of the reaction provided both Ph3As and Cul were added. Additional manipulations of 77 resulted in the synthesis of (+)-epibatidine (78). 

The addition of LiCl and Cul, and triphenylarsine as ligand are required to suppress side-reactions in the carbonylative cross-coupling of geminally substituted alkenyl triflate in the synthesis of sarcodictyin. Stereochemical configuration of the double bond of organotin compound was completely lost in this reaction (Equation (5)). " ... 

The application of triphenylarsine ligand and LiCl as promoter allows for realization of carbonylative crosscoupling in complex synthetic tasks, as shown, for example, in Equations (6) and (7). ... 

The Stille reaction was also effective in the coupling of two sensitive substrates. The functionalised dihydropyrrole and vinylstannane shown in 6.29. were reacted under very mild conditions to give, after an acidic workup, the 2-acylpyrrole derivative.39 The palladium catalyst contained the less strongly coordinating triphenylarsine ligand instead of triphenylphosphine, a trick commonly used to increase the efficiency of the Stille coupling. 

Farina, V. Krishnan, B. Large Rate Accelerations in the Stille Reaction with Tri-2-furylphosphine and Triphenylarsine as Palladium Ligands Mechanistic and Synthetic Implications, J. Am. Chem. Soc. 1991,113, 9585-9595. 

Platinum also catalyzes hydrocarboxylation, under comparable reaction conditions (240 bar, 80 C). The best ligand in this case is triphenylarsine and a 10-fold excess of tin(II) chloride provides even higher selectivity to the linear ester (entry 4, Table 5).78... 

He, H.S., Zhang, C., Ng, C.K.-W. and Toy, P.H. (2005a) Polystyrene-supported triphenylarsines useful ligands in palladium-catalyzed aryl halide homocoupling reactions and a catalyst for alkene epoxidation using hydrogen peroxide. Tetrahedron, 61(51), 12053-57. 

The most important complex of this type is [Rh(NO)Cl2(PPh3)2], which was first prepared in 1962. The tri(cyclohexyl)phosphine and triphenylarsine analogs were also prepared at this date. The dichloro complexes were precipitated when excess neutral ligand was allowed to react with [Rh(NO)2Cl],. The preparative routes available for [Rh(NO)Cl2(PPh3)2] are summarized in Scheme 43. Again AT-methyl-lV-nitrosotoluene-p-sulfonamide is the most convenient source of the nitrosyl ligand.202,1323... 

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