A Phosphane‐Free Catalyst System for the Heck Arylation of Disubstituted Alkenes: Application to the Synthesis of Trisubstituted Olefins

Abstract

A new general procedure for the Heck arylation of disubstituted olefins is described. This procedure allows, in many instances, the stereoselective synthesis of trisubstituted olefins. Trisubstituted olefins are easily accessible under mild reaction conditions using a new catalyst system consisting of dicyclohexylamine or methyl-(dicyclohexyl)amine and a phase-transfer catalyst. The choice of base was found to be crucial for the rate and stereoselectivity of the Heck arylation reactions. This method is applicable to the coupling of both electron-deficient and electron-rich aryl halides and displays good stereoselectivity and a high degree of functional group compatibility. Labeling studies indicate that the source of this selectivity is thermodynamic in nature.

Strong evidence of solution-phase catalysis associated with palladium leaching from immobilized thiols during Heck and Suzuki coupling of aryl iodides, bromides, and chlorides

“…The higher conversion of bromoacetophenone found when using sodium acetate instead of organic base was not observed for iodobenzene; instead, the opposite was true, with higher conversions achieved when NEt 3 rather than NaOAc was used as the base. Using methyl(dicyclohexyl)amine (MDA), a base previously described as more active for couplings involving activated aryl bromides [57], produced no activity with bromoacetophenone but significant activity for iodobenzene. Thus, the exact role of the base on activity is currently not clear with respect to leaching or stabilization of the leached catalytic species.…”

Pd–benzothiazol-2-ylidene complex in ionic liquids: Efficient catalyst for carbon–carbon coupling reactions

“…For this reason, to activate the aryl bromides in these ILs, the addition of phosphines as ligands is indispensable [20]. As the previous reports [4,[21][22][23] on the Heck reaction recognized that the addition of tetraalkylammonium or tetraphenylphosphonium salts to conventional solvents led to higher catalytic activity, we decided to perform this reaction in tetrabutylammonium bromide (TBAB) as solvent [24]. The complex 3 proved to be an excellent catalyst in the phosphine-free Heck reaction of the aryl bromides and activated aryl chlorides in TBAB (Scheme 2) [25].…”

“…In most of the papers dedicated to the Heck reaction, no more than few examples have been reported dealing with methacrylates as olefin acceptors [23,26]. Among these, it was reported [27] that the arylation of 3-hydroxy-2-methylenealkanoates affords b-oxoalkanoates (Scheme 3).…”

The Role of Palladium Nanoparticles as Catalysts for Carbon–Carbon Coupling Reactions

“…Bumagin reported the use of 1 mol% of ligand free Pd(OAc) 2 in the Heck reaction of acrylic acid with a number of substituted bromarenes in water, using Na 2 CO 3 as base [71] . Buchwald reported the Heck reaction of bromoarenes using 1 -4 mol% of Pd(OAc) 2 with Et 4 NCl in DMA under relatively mild conditions (85 -100 ° C) [72] . In his chemistry the use of the hindered bases dicyclohexylamine or methyldicyclohexylamine was essential.…”