Diene complexes hydroamination

Hydroamination of allenes and 1,3-dienes in the presence of Ni(II), Pd(II), and Rh(III) complexes yields product mixtures composed of simple addition products and products formed by addition and telomerization.288 Nickel halides308 and rhodium chloride309 in ethanol [Eq. (6.51)] and Pd(n) diphosphine complexes310 are the most selective catalysts in simple hydroamination, while phosphine complexes favor telomerization 288... 

The latter transformation requires the use of a small amount of an acid or its ammonium salt. By using [Cp2TiMe2] as the catalyst, primary anilines as well as steri-cally hindered tert-alkyl- and sec-alkylamines can be reacted.596 Hydroamination with sterically less hindered amines are very slow. This was explained by a mechanism in which equlibrium between the catalytically active [L1L2Ti=NR] imido complex and ist dimer for sterically hindered amines favors a fast reaction. Lantha-nade metallocenes catalyze the regiospecific addition of primary amines to alkenes, dienes, and alkynes.598 The rates, however, are several orders of magnitude lower than those of the corresponding intramolecular additions. 

Ph3PAuOTf has been shown to catalyse intra- and inter-molecular hydroamination of unactivated alkenes with sulfonamides in a Markovnikov fashion.115 The same complex catalyses hydroamination of 1,3-dienes with carbamates (e.g. PhCH2OCONH2) and sulfonamides at room temperature.116 An intramolecular version of the hydroamination with the Cbz group (benzyloxycarbonyl) has also been reported. The latter... 

The intermolecular hydroamination of alkynes, catalysed by the aquapalladium complex [(dppe)Pd(H20)2](0Tf)2, has been reported. The reaction is believed to proceed through the equilibrium between the hydroxopalladium and the amidopalladium complexes, followed by aminopalladation of alkynes.76 Regioselective 1,2-diamination of 1,3-dienes by dialkylureas, catalysed by (MeCN)2PdCl2 in the presence of 1 equiv. of / -benzoquinone, has been developed as a highly efficient method.77... 

Several catalytic systems have been investigated for hydroamination of unsaturated bonds [16]. Takahashi et al. reported the telomerization of 1,3-dienes in the presence of an amine leading to octadienylamine or allylic amines when palladium catalysts are used in association with monodentate or bidentate phosphine ligands, respectively [17]. Dieck et al. demonstrated the beneficial effect of addition of an amine hydroiodic salt in the hydroamination reaction of 1,3-dienes in which the allylic amines are produced via an intermediate Jt-allyl palladium complex [18]. Coulson reported the Pd-catalyzed addition of amines to allenes where dimerization is incorporated [4]. This reaction presumably proceeds via a cyclic palladium intermediate in which the Pd activates the olefinic bond for nucleophilic attack the reactions are therefore different from pronucleophilic additions. 

Type 4 metallocene complexes catalyze the regioselective mtermolecular addition of primary amines to acetylenic, olefinic, and diene substrates at rates which are = 1/1000 those of the most rapid intramolecular analogues [165]. Variants such as the intramolecular hydroamination/cyclization of aminoallenes [166] and the intra- and intermolecular tandem C-N and C-C bond-forming processes of aminodialkenes, aminodialkynes, aminoallenynes, and aminoalkynes [167] were applied as new regio- and stereoselective approaches to naturally occurring alkaloids. For example, bicyclic pyrrolizidine intermediate E... 

Organolanthanide-catalyzed intermolecular hydrophosphination is a more facile process than intermolecular hydroamination. The reaction of alkynes, dienes, and activated alkenes with diphenylphosphine was achieved utilizing the ytterbium imine complex 9 (Fig. 8) as catalyst [185-188]. Unsymmetric internal alkynes react regioselectively, presumably due to an aryl-directing effect (48) [186]. 

No dimerization of substituted or cyclic dienes occurs by using Pd-PPh3 as a catalyst under usual conditions, instead the 1 1 adducts are formed. For example, dimerization of isoprene using Pd-PPh3 is slow. 1,2-Hydroamination of 1-phenyl-butadiene with aniline proceeded to afford the amine 15, and two products 16 and 17 were obtained from isoprene when an exotic Pd complex 18 was used as a catalyst [6]. 

Preparation of aliphatic amines by direct hydroamination of alkenes with amines is a highly desirable reaction. However, except for the well-established hydroamination of 1,3-dienes via 7r-allylpalladiums, no smooth hydroamination of simple alkenes is known. As a breakthrough, Kawatsura and Hartwig reported that the hydroamination of styrene derivatives with aniline is catalyzed by Pd(TFA)2 and DPPF in the presence of trifluoroacetic acid (TFA) or triflic acid as a cocatalyst to afford the branched amine 24 regioselectively in 99 % yield. Formation of the branched amine 24 offers an opportunity of asymmetric amination. They obtained the (5)-amine 25 in 80 % yield with 81 % ee using (/ )-BINAP as a chiral ligand [14]. The reaction is explained by insertion of styrene to the H-Pd bond and nucleophilic attack of amine on an fj -benzylpalladium complex [15]. Hii and coworkers obtained the amine 24 with 70 % ee in 75 % yield using the dicationic Pd complex, [Pd(MeCN)(H20)(/ -BINAP)](0Tf)2 [16]. 

Allyl ligands are reactive groups in catalytic processes, such as allylic substitution (Chapter 20) and transition-metal-catalyzed additions of allyl groups to carbonyl compounds (Chapter 12). They are also intermediates in a variety of catalytic processes involving dienes, including the hydroamination (Chapter 16) and telomerization of dienes (Chapter 22). They are also formed by cleavage of the allylic C-H bonds of olefins to form intermediates in allylic oxidation chemistry and as stable species that inhibit the polymerization of a-olefins (Chapter 22). The synthesis, structure, and occurrence of -rj -allyl complexes have been reviewed. ... 

Lanthanide complexes also catalyze the hydroamination of 13-dienes. The lanthanide catalysts originally developed for the intramolecular hydroamination of aminoalkenes are particularly active for the intramolecular additions of alkyl amines to dienes. The scope of this process is broad an illustrative example showing the high diastereoselectiv-ity of the cyclization of a chiral amine is shown in Equation 16.82. These reactions occur by insertion of the diene into a lanthanide-amide intermediate to form an allyl-metal intermediate. 

Oxidative addition of allylic amines to Ni(0) precursors in the presence of acid has been shown to lead to cationic (allyl)Ni complexes. Thus, Ni(cod)(dppf) reacts with a range of cyclic allylic amines in the presence of trifluoroacetic acid (TFA) to generate complexes 74, as shown in Scheme 22. " This process can proceed by protonation of the amine and the oxidative addition of the resulting ammonium salts, as above. The same system or a mixture of Ni(cod)2 and dppf catalyzes the hydroamination of dienes. In this case, the catalysis is thought to proceed via the initial protonation of Ni(0) precursor to give an Ni-H species that undergoes insertion of the diene to generate an allyl... 

Intramolecular hydroamination of protected amino-1,3-dienes has been shown to produce five- and six-membered heterocyclic homoallylic amines when the tridentate PNP pincer complex of palladium(II) (68) is employed as a catalyst (5 mol%). " ... 

Reaction Mechanism-. The preferential anfi-Markovnikov or 2,1-addition to styrene can be attributed to the organization of the transition state to N-C bond formation. Factors that stabilize the developing anionic charge upon the atom adjacent to the metal center in the transition state to N-C bond formation will be expected to lower the activation energy of the insertion step [98,99]. In the case of the 2,1-insertion of styrene into the Ca-N bond the phenyl group may stabilize the adjacent anionic center. In the case of a 1,2-insertion, no such stabilization exists. The product distribution for the hydroamination of dienes can be explained by invoking a metal allyl complex upon addition of M-NR2 to the diene. 

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). 

The hydroamination of dienes with basic primary and secondary amines can be achieved with a variety of catalysts including aUcah metals and their readily available derivatives. Reactions of acyclic 1,3-dienes catalyzed by alkah metals [159, 160, 171], metal hydrides [172], and metal amides (generated from metal alkyls) [163, 173, 174] result in regioselective formation of the stericaUy less hindered 1,4-addition product in most cases (23) [174]. Primary aliphatic amines are capable of performing double hydroamination in these conditions, typically leading to complex mixtures of mono- and bis-aUyl amines, whereas reactions with secondary amines are more practical [160]. 

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