Cyclohexadiene hydroamination

Figure 1 Use of a simple spot test to screen catalysts for the hydroamination of cyclohexadiene with aniline.

The Brpnsted acidic anilinium salt [PhNH3+][ B(C6F5)4] has been developed as a catalyst for the hydroamination and hydroarylation of alkenes, such as styrenes, nor-bomene, cyclic alkenes, and cyclohexadiene, with anilines. The weakly coordinating... 

The direct catalytic reaction of nucleophiles such as amines with 1,3-dienes to give allylic amines is difficult to achieve. A high-throughput assay was used to screen catalysts for the 1 1 hydroamination of aniline to 1,3-cyclohexadiene (equation 44). ... 

The palladium catalyzed asymmetric hydroamination of cyclohexadiene with arylamines utilizing a variant of Trost s ligand R,R) 61 proceeds with high enantio selectivities under mild conditions (Scheme 11.19) [21]. The mechanism is believed to follow a similar pathway as proposed for palladium catalyzed hydroamination of vinyl arenes (Scheme 11.2) [17]. 

Scheme 11.19 Palladium catalyzed asymmetric hydroamination of cyclohexadiene [21].

Hy droamination aniline plus cyclohexadiene Hydroamination alkylamines plus functionalized olefins Heck coupling of solid-supported aryl bromides and chlorides with fluorescent olefins... 

Hydroamination of prochiral cyclic dienes such as 1,3-cycloheptadiene (19) with aniline gave rise to 3-(A/ -phenylamino)cycloheptene (20) smoothly using Pd-PPh3. This reaction suggests the possibility of asymmetric amination. Actually Hartwig carried out successful asymmetric hydroamination of 1,3-cyclohexadiene with 4-aminobenzoate using (R, 7 )-(XIII-l) as a chiral ligand and obtained N-(3-cyclohexenyl)-4-aminobenzoate (21) in 83 % yield with 95 % ee [7],... 

More recently, the hydroamination of butadiene, isoprene, and cyclohexadiene to form 1 1 adducts with high selectivity catalyzed by nickel and palladium complexes has... 

The reaction also works well with acyclic dienes to give hydroamination products in high yields. In one of the studies, trifluoroacetic acid was used in catalytic amounts to increase the rate of the reaction [26aj. In the latter study, the use of chiral ligands in the hydroamination of 1,3-cyclohexadiene afforded products with up to 95% ee. 

In another ligand effect investigation, Ozawa and coworkers [260] probed the effect of new ferrocene-derived chelating phosphine ligands (Figure 15.8) in the hydroamination of cyclohexadiene with aniline. While the desired product was observed, the long reaction times ensure that this catalyst is not competitive with the state-of-the-art Pd catalysts for diene hydroamination [93]. 

Dienes were also subjected to the hydroamination reaction in the presence of Pd catalysts such as the 1. A colorimetric assay showed that among various catalysts, complex formed from [Pd( j -allyl)Cl]2 and PPh3 is the most active. The pyridyl derivative is obtained in 88% yield (eq 94). The enantioselective addition was also optimized for allylic amine formation in good yield and 95% enantiomeric excess. Furthermore a range of arylamines could react with cyclohexadiene in 86-95% ee and 59-83% yield (eq95). 

They also developed the Cu(OTf)2-catalyzed enantioselective alkene hydroamination/cyclization to enantioenriched 2-methylindolines using 1,4-cyclohexadiene as hydrogen atom source. 1,4-Cyclohexadiene is relatively... 

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