Hydroamination lanthanide catalyst

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]. 

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. 

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). 

Intermolecular additions of primary amines to alkenes have also been reported using lanthanide catalysts. These reactions, although slow, do occur to high conversion. Similar to hydroaminations catalyzed by late transition metal complexes, these reactions form the products from Markovnikov addition of the N-H bond across the olefin. One example of such a reaction is shown in Equation 16.59. ... 

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. 

Hong S, Tian S, Metz MV, Marks TJ. C2-Symmetric bis(oxazolinato)lanthanide catalysts for enantioselective intramolecular hydroamination/cyclization. J. Am. Chem. Soc. 2003 125(48) 14768-1478. 

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). 

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>. 

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. 

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. 

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... 

Catalytic asymmetric hydroamination of alkenes can be achieved using early and late transition metal catalysts and lanthanide-based catalytic... 

These intramolecular hydroaminations lead to the formation of chiral products. Thus, several studies have been devoted to developing ligands for enantioselective, intramolecular hydroaminations of olefins catalyzed by lanthanide complexes. ° Selectivities of these reactions with chiral cyclopentadienyl derivatives have been modest. Selectivities have been higher with catalysts containing non-cyclopentadienyl ligands. Some of tlie most selective catalysts are the yttrium complexes of the bis(thiolate) ligands reported by Livinghouse, the scandium and lutetium complexes of 33 -disubstituted binaphtholates reported by Hultzsch, and the BINAM-based bisamidates of Schafer.- A representative cyclization catalyzed by a member of each of these classes of catalyst are shown in Equation 16.64. 

Catalysts for tfie additions of amines to vinylarenes have also been developed. These catalytic reactions include some of the first hydroaminations of unstrained olefins catalyzed by late transition metals, as well as examples catalyzed by lanthanide complexes. These additions occur with Markovrukov selectivity with one set of catalysts and with anti-Markovnikov selectivity with several others. These additions occur by several different mechanisms that are presented in Section 16.5.3.2. 

The hydroamination of 1,3-dienes has been known for many years, but these reactions have often generated mixtures of products. More recently, the intermolecular and intramolecular hydroamination of dienes has been reported with lanthanide and palladium catalysts to generate allylic amines in high yields. These reactions have also occurred with high enantioselectivity in some cases. 

Some of the most active catalysts for the hydroamination of alkynes are based on lanthanides and actinides. The turnover frequencies for the additions are higher than those for lanthanide-catalyzed additions to alkenes by one or two orders of magnitude. Thus, intermolecular addition occurs with acceptable rates. Examples of both intermolecular and intramolecular reactions have been reported (Equations 16.87 and 16.88). Tandem processes initiated by hydroamination have also been reported. As shown in Equation 16.89, intramolecular hydroamination of an alk5me, followed by cyclization with the remaining olefin, generates a pyrrolizidine skeleton. Hydroaminations of aminoalkynes have also been conducted with the metallocenes of the actinides uranium and thorium. - These hydroaminations catalyzed by lanthanide and actinide complexes occur by insertion of the alkyne into a metal-amido intermediate. 

As discussed in Chapter 9, the insertion of olefins and alk)nes into metal-amido complexes is limited to a few examples. Such insertion reactions are proposed to occur as part of the mechanism of the hydroamination of norbomene catalyzed by an iridium(I) complex and as part of the hydroamination of alkenes and alkynes catalyzed by lanthanide and actinide metal complexes. This reaction was clearly shown to occur with the iridium(I) amido complex formed by oxidative addition of aniline, and this insertion process is presented in Chapter 9. The mechanism of the most active Ir(I) catalyst system for this process involving added fluoride is imknown. 

The hydroamination of alkenes and alkynes has been of longstanding interest in organometallic chemistry [26]. Much of the early work in this area focused on early transition metal or lanthanide metal catalyst systems. However, much recent progress has been made in late-metal catalyzed hydroamination chemistry, and several interesting hydroamination reactions that afford nitrogen heterocycles have been developed using palladium catalysts. 

Qrganolanthanides such as metallocene or halfmetallocene andnomnetallocene lanthanide amides, alkylides, and hydrides are highly efficient catalysts for the intramolecular hydroamination/cyclization of a wide range of substrates such as aminoalkenes (Scheme 2), aminoalkynes, aminoal-lenes, and aminodienes. ... 

Many transition metals and lanthanide-based complexes have been shown to catalyze (5.7.2)-type hydroamination reactions. In many cases the catalysts based on lanthanides are found to have significant activity. Structures 5.70 and 5.71 are two typical examples of transition metaland lanthanide-based precatalysts. 

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