32604-29-8Relevant articles and documents
Replacing conventional carbon nucleophiles with electrophiles: Nickel-catalyzed reductive alkylation of aryl bromides and chlorides
Everson, Daniel A.,Jones, Brittany A.,Weix, Daniel J.
supporting information; experimental part, p. 6146 - 6159 (2012/05/07)
A general method is presented for the synthesis of alkylated arenes by the chemoselective combination of two electrophilic carbons. Under the optimized conditions, a variety of aryl and vinyl bromides are reductively coupled with alkyl bromides in high yields. Under similar conditions, activated aryl chlorides can also be coupled with bromoalkanes. The protocols are highly functional-group tolerant (-OH, -NHTs, -OAc, -OTs, -OTf, -COMe, -NHBoc, -NHCbz, -CN, -SO2Me), and the reactions are assembled on the benchtop with no special precautions to exclude air or moisture. The reaction displays different chemoselectivity than conventional cross-coupling reactions, such as the Suzuki-Miyaura, Stille, and Hiyama-Denmark reactions. Substrates bearing both an electrophilic and nucleophilic carbon result in selective coupling at the electrophilic carbon (R-X) and no reaction at the nucleophilic carbon (R-[M]) for organoboron (-Bpin), organotin (-SnMe3), and organosilicon (-SiMe2OH) containing organic halides (X-R-[M]). A Hammett study showed a linear correlation of σ and σ(-) parameters with the relative rate of reaction of substituted aryl bromides with bromoalkanes. The small ρ values for these correlations (1.2-1.7) indicate that oxidative addition of the bromoarene is not the turnover-frequency determining step. The rate of reaction has a positive dependence on the concentration of alkyl bromide and catalyst, no dependence upon the amount of zinc (reducing agent), and an inverse dependence upon aryl halide concentration. These results and studies with an organic reductant (TDAE) argue against the intermediacy of organozinc reagents.
Coupling of Aryl Chlorides by Nickel and Reducing Metals
Colon, Ismael,Kelsey, Donald R.
, p. 2627 - 2637 (2007/10/02)
An efficient synthesis of biaryls (diarenes) from aryl chlorides has been developed and investigated.The coupling reagent is a catalytic mixture of anhydrous nickel salt and triphenylphosphine in the presence of a reducing metal (Zn, Mg, or Mn).The reaction occurs rapidly under mild conditions, tolerates a variety of functional groups, employs air-stable starting materials, and can be run conveniently in ordinary laboratory glassware.Excess reducing metal drives the coupling process and allows even aryl chlorides to be coupled to high yields, a distinguishing advantage over previous coupling processes which employed stoichiometric zero-valent nickel reagents.The reaction is pseudo-zero-order in aryl chloride and is promoted by 2,2'-bipyridine and by halide salts (F Cl Br I).A number of reaction variables have been examined and their effects on the kinetics and yields are discussed.Reduction and aryl transfer from triphenylphosphine, the major side reactions, can be minimalized in most cases.A coupling mechanism consistent with the observed kinetics and reaction parameters is proposed in which the key step is reduction of an arylnickel species by zinc to an arylnickel(I) complex.
