Palladium-catalyzed amination palladacycles

The first palladium-catalyzed coupling between a secondary amine and an aryl chloride was described by Beller, Hermann and co-workers in 1997 [70]. Use of palladacycle 12 as catalyst resulted in C-N bond formation in good yield for several secondary amines and electron-deficient aryl chlorides, Eq. (40). In these transformations, varying amounts of the regioisomeric product was observed, indicative that to some degree the reaction proceeds via a benzyne intermediate. 

In 2012, Chen and coworkers developed the palladium-catalyzed intramolecular amination of C(sp )-H at y and 5 positions to synthesize a series of nitrogen-containing heterocycles [15], including azetidine (Scheme 2.11), pyrrolidines, and indolines. With the optimal conditions, using catalytic Pd(OAc)2, an oxidant (PhI(OAC)2, 2.5 equiv.) and an acid additive (AcOH) in toluene at llO C, Chen tested them on other picolinamide substrates bearing primary y-C(sp )-H bonds surprisingly, the seemingly unfavorable four-membered azetidine was obtained as the major product. It is possible that a Pd(IV) intermediate was formed via PhI(OAC)2 oxidation of the palladacycle intermediate because the subsequent C-N and C-O reductive elimination pathways would lead to the formation of the cyclized and acetoxylated product. It was also noteworthy that no P H elimination product was detected under the aforementioned reaction conditions. 

Gladysz showed that a thermomorphic fluorous paUadacyde acts as a PdNP catalyst precursor for the Heck reaction at 80-140 C in DMF with very high turnover numbers [24a]. Molecular palladium complexes such as palladacycles and other palladium salts have also been used as PdNP precursors upon treatment with CO in DMF or toluene at room temperature, and these PdNPs catalyzed nudeophiUc substitution/carbonylation/amination affording iso-indolinones at room temperature [24bj. PdNPs capped with spedal ligands such as polyoxometal-... 

It was also recently demonstrated that homocoupling of aryl and heteroaryl iodides could be efficiently catalyzed either by a palladacycle catalyst in the presence of amine in or by a (7r-allyl)palladium complex and TBAF in DMSO. Also, homocoupling of a variety of substituted halothiophenes was achieved in the presence of a catalytic amount of Pd(OAc)2 and diisopropylethylamine in toluene. ... 

Sigmatropic Rearrangement of Trichloroacetimidates The development of the asymmetric palladium(II)-catalyzed [3,3]-sigmatropic rearrangement of trichloroacetimidates has proven to be a powerful method for the generation of chiral amines from achiral allylic alcohols [12]. In particular, the cobalt oxazoline palladacycles, such as COP-Cl (4), have been shown to be particularly efficient for this transformation (Scheme 5.1) [13]. 

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