Cu(I)/Pd(0)-Catalyzed Cross-Coupling Reaction of Alkynylsilanes with Aryl or Alkenyl Triflates: “Sila”-Sonogashira-Hagihara Coupling

Abstract

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C(sp2)‐C(sp) and C(sp)‐C(sp) Coupling Reactions Catalyzed by Oxime‐Derived Palladacycles

“…[1] Two of the most useful synthetic transformations of alkynes are the Sonogashira±Hagihara reaction [2] (palladium/coppercatalyzed cross-coupling reactions of sp 2 -C to sp-C atoms) or the silane version of the process employing alkynylsilanes (sila-Sonogashira reaction [3] ), and the palladium-catalyzed acetylenic oxidative homocoupling reaction between their sp-carbon atoms, called the Glaser-type process. [4] The Sonogashira coupling of terminal acetylenes with sp 2 -C atoms, provides a useful tool for the preparation of alkyl-, aryl-, and diaryl-substituted acetylenes (Eq.…”

“…The reaction is typically carried out in the presence of copper(I) salts as co-catalysts, and employing amines as solvents. Most frequently, high loadings of palladium (0.1 ± 5 mol %) and varying amounts of CuI are required when typical catalysts such as Pd(PPh 3 ) 2 Cl 2 , Pd(PPh 3 ) 4 or Pd 2 (dba) 3 are employed. With respect to the methodologies that employ CuI as co-catalyst, Buchwald and Fu, [5] have described Pd(PhCN) 2 Cl 2 / CuI/P(t-Bu) 3 as a versatile catalyst system for the Sonogashira reaction of aryl bromides at room temperature (TON up to 200).…”

“…Most frequently, high loadings of palladium (0.1 ± 5 mol %) and varying amounts of CuI are required when typical catalysts such as Pd(PPh 3 ) 2 Cl 2 , Pd(PPh 3 ) 4 or Pd 2 (dba) 3 are employed. With respect to the methodologies that employ CuI as co-catalyst, Buchwald and Fu, [5] have described Pd(PhCN) 2 Cl 2 / CuI/P(t-Bu) 3 as a versatile catalyst system for the Sonogashira reaction of aryl bromides at room temperature (TON up to 200). Using an excess of a bulky and electron-donating ligand such as P(t-Bu) 3 (6 mol %) and a high catalyst loading (3 mol % of Pd), these authors could effect the Sonogashira coupling using only an equimolar amount of amine.…”

“…With respect to the methodologies that employ CuI as co-catalyst, Buchwald and Fu, [5] have described Pd(PhCN) 2 Cl 2 / CuI/P(t-Bu) 3 as a versatile catalyst system for the Sonogashira reaction of aryl bromides at room temperature (TON up to 200). Using an excess of a bulky and electron-donating ligand such as P(t-Bu) 3 (6 mol %) and a high catalyst loading (3 mol % of Pd), these authors could effect the Sonogashira coupling using only an equimolar amount of amine. On the other hand, Mori has carried out the Sonogashira coupling of terminal alkynes with aryl iodides and bromides at room temperature in the presence of Pd(PPh 3 ) 2 Cl 2 in THF with aqueous ammonia as base.…”

“…[6] Very recently, Plenio and colleagues [7] have presented a new and very efficient catalytic system for the Sonogashira coupling of activated and non-activated aryl chlorides with terminal acetylenes, based on the combination Na 2 PdCl 4 /(1-Ad) 2 PBn/CuI (1-Ad 1-adamantyl, Bn benzyl). On the other hand, N-heterocyclic carbene palladium(II) complex 1, [8] has also been shown to mediate the Sonogashira coupling of aryl bromides with different alkynes at 80 0 C in DMF under inert atmosphere, in the presence of 2 mol % of CuI and 1 mol % of PPh 3 . However, and in order to simplify the reaction protocol, copper-free methodologies have lately attracted most attention, as the use of copper(I) salts as co-catalysts usually induces the homocoupling reaction (Glasertype [4] ) of terminal alkynes to diynes in the presence of oxygen as well as the precipitation of catalytically inactive palladium black.…”