Lanthanides, hydroamination

In 2003, Livinghouse et al. also reported that chelating bis(thiophosphonic amidates) complexes of lanthanide metals, such as yttrium or neodymium, were able to catalyse intramolecular alkene hydroaminations. These complexes were prepared by attachment of the appropriate ligands to the metals by direct metalation with Ln[N(TMS)2]3- When applied to the cyclisation of 2-amino-5-hexene, these catalysts led to the formation of the corresponding pyrrolidine as a mixture of two diastereomers in almost quantitative yields and diastereos-electivities of up to 88% de (Scheme 10.81). 

The synthesis of a series of chiral organophosphine oxide/sulfide-substituted binaphtholate ligands has recently been reported by Marks and Yu and their corresponding lanthanide complexes characterized. These complexes, generated in situ from Ln[N(TMS)2]3, cleanly catalysed enantioselective intramolecular hydroamination/cyclisation of 1-amino-2,2-dimethyl-4-pentene albeit with a low enantioselectivity of 7% ee (Scheme 10.82). 

A lanthanide-mediated, sequential hydroamination/C-C cyclization reaction served to prepare the benzo[ ]quino-lizine derivative 358 from precursor 357, using a Nd species as a catalyst (Equation 12). This cascade process proceeded in good yield and with high diastereoselectivity <2003T10581>. 

The utility of a new lanthanide catalyst 162 for hydroamination and hydrosilylation is highlighted below<06CC874>. Application of this new lanthanide catalyst resulted in excellent yields of piperidines such as 163 and 164 with reduced reaction times. 

Such lanthanide catalysts were also used in hydroamination/cyclization strategies for the synthesis of the alkaloid (+)-xenovenine. This reaction of enantiomerically pure 147 leading to 148 via two C-N bond formations was used in a late step of the synthesis after a hydrogenation, the natural product was isolated (Scheme 15.46) [100]. 

Alkene hydroamination has been known for many years, but has been little used as a method in organic synthesis. Tobin Marks of Northwestern recently published a series of three papers that will make this transformation much mote readily accessible. In the first (J. Am. Chem. Soc. 125 12584,2003) he describes the use of a family of lanthanide-derived catalysts for intermolecular hydroamination of alkynes (to make imines, not illustrated) and alkenes. With aliphatic amines, the branched (Markownikov) product is observed, 1 — 2. With styrenes, the linear product is formed. When two alkenes are present, the reaction can proceed (3 —> 4) to form a ring, with impressive regioselectivity. 

Intramolecular hydroamination of amino alkenes.1 This lanthanide effects cy-clization of amino alkenes in hydrocarbon solvents to five- and six-membered nitrogen heterocycles. 

Intramolecular addition of amine N-H bonds to carbon-carbon multiple bonds would afford nitrogen heterocycles. To realize catalytic cyclization of a,co-aminoalkenes or aminoalkynes, various catalytic systems have been developed especially with early transition metals such as titanium, zirconium, lanthanide metals, and actinide metals [ 12], Late-transition-metal catalysis based on Ni, Pd, and Rh has also proved to be efficient [ 12], Recently, the ruthenium-catalyzed intramolecular hydroamination of aminoalkynes 15 was reported to afford 5-7-membered ring products 16 in various yields (Eq. 6) [13]. Among... 

The catalytic activity of the Cp LnR complexes in hydroamination/cyclization of aminoolefins has been documented in terms of lanthanide size and other factors [186]. 

The C2-symmetric bisoxazolinate 175 formed complexes with lanthanides for the catalysis of enantioselective intramolecular hydroamination /cyclization <03JA14768>. 

Hong, S., Xian, S., Metz, M.V. et al. (2003) C2-symmetric bis(oxazoUnato)lanthanide catalysts for enantioselective intramolecular hydroamination/cycUzation. Journal of the American Chemical Society, 125, 14768. 

A different mechanism again is involved in the hydroamination reaction catalyzed by lanthanide complexes, Cpff.nR which is applied to the cyclization of unsaturated amines. The mechanism involves the formation of a metal amide species from both the catalysts (by different routes), followed by the turnover —limiting intramolecular insertion of the alkene to give a cr-complex, from which the decomplexed cyclic amine is obtained after reaction with a second molecule of the unsaturated amine19,20,107. 

To catalyze the direct hydroamination of olefins according to eq. (1) two basic approaches have been employed involving primarily the activation either of the amine or of the olefin. One possible way to activate the amine for catalysis is the transformation to the much stronger nucleophilic amide ion by deprotonation. Thus, the amides of strongly electropositive metals, such as alkali metals, alkaline earth metals, or lanthanides, are able to react with the C-C double bond under... 

When Marks and co-workers [10] published their investigations of the organo-lanthanide-catalyzed intramolecular hydroamination of appropriate a,ai-amino-lefms, the opened a useful synthetic route to different types of cyclic amines (Scheme 4) in combination with a thorough analysis of the catalytic reaction mechanism and the structure-reactivity relationships. 

Organo-/-element-catalyzed hydroaminations have been extensively investigated for more than 10 years.1034-1038 Lanthanide metallocenes catalyze the regiospecific intermolecular addition of primary amines to acetylenic, olefinic, and diene substrates at rates which are —1/1000 those of the most rapid intramolecular analogs. Kinetic and mechanistic data argue for turnover-limiting C=C/C=C insertion into an Ln-N bond, followed by protonolysis of... 

The scope of the lanthanide-mediated, intramolecular amination/cyclization reaction has been determined for the formation of substituted quinolizidines, indolizidines, and pyrrolizidines,1046 as well as tricyclic and tetracyclic aromatic nitrogen heterocycles.1047 The amide derivative OT ro-[ethylene-bis(indenyl)]ytterbium(m) bis(trimethyl-silyl)amide catalyzes the hydroamination of primary olefins in excellent yields.701 A facile intramolecular hydroamination process catalyzed by [(C5H4SiMe3)2Nd(/r-Me)]2 has also been reported. The lanthanide-catalyzed hydroamination enables a rapid access to 10,1 l-dihydro-5//-dibenzo[tf,rf]cyclohepten-5,10-imines (Scheme 283).1048... 

In the same year, the first structurally defined biaryl diamide complexes as enantioselective intramolecular hydroamination catalysts were reported by Schulz and coworkers. They are the first example of lanthanide catalysts supported by a binaphthyl diamide ligand. 2 equiv of the lithium salt of the binaphthyl diamide ligand Li2L41 and anhydrous LnCls in THF at ambient temperature generated ate complexes [Li(THF)4][Ln(L41)2] (Ln = Sm 197 and Yb 198) via salt elimination (Scheme 76). 

Within the past 10 years, several classes of postmetallocenes of the lanthanides, especially the monoanionic amido metal complexes, were developed as homogeneous catalysts. These compounds were basically used in two fields, C-C multibond transformations and the polymerization catalysis. In the area of multibond transformations, the hydroamination and the hydrosilylation reaction were most intensely... 

During the last two decades, lanthanide catalysis has been extensively explored [3], considering the unique properties and the absence of toxicity of these "heavy" metals which make them environmentally friendly. Olefin transformations catalysed by organolanthanides such as oligomerisation, hydrogenation, hydrosilylation, hydroamination, polymerisation, have attracted much attention. The two latter reactions can be initiated by hydrides (which act as precatalysts, such as for MMA polymerisation [4]), but do not involve hydrides as intermediates in the catalytic cycle and therefore will not be considered in the present review. 

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