Palladium-catalyzed carbon-nitrogen bond formation, bases

In certain cases, when the palladium or nickel catalyzed coupling is not efficient or fails completely, an alternate solution is provided by the use of copper based catalyst systems. The 5-iodouracil derivative shown in 7.77. was unreactive towards imidazole using either the Buchwald-Hartwig conditions or the copper(I) triflate promoted the carbon-nitrogen bond formation reported by Buchwald98 These latter conditions, however, were effective in coupling the iodouracil with a series of other amines (7.77.), The optimal catalyst system consisted of copper(I) triflate, phenantroline and dibenzylideneacetone (dba).99... 

Since its discovery by Tsuji [15,16] and catalytic expansion by Hata [17] and Atkins [18], allylic substitution has become the most popular palladium-catalyzed method for carbon-carbon bond formation along with crosscoupling reactions. However, the first report using NHC in this transformation only appeared recently [19]. An imidazolium salt with a bulky substituent on the nitrogen atoms, IPr HC1, was found to be a suitable ligand for allylic substitution with soft nucleophiles (Scheme 2). Pd2(dba)3 as palladium source and Cs2C03 as base completed the catalyst system. 

---