Intramolecular hydroamination of conjugated enynes

An intramolecular hydroamination of conjugated enyne was developed using commercially available n-BuLi as a precatalyst. This hydroamination reaction led to products with allene and pyrrolidine functional groups. One of the enyne hydroamination products was successfully converted to natural products irniine and irnidine in three steps. The scope and mechanism of the enyne hydroamination are also discussed.     

Base-catalyzed intramolecular hydroamination of conjugated enynes

A de novo intramolecular hydroamination of conjugated enynes was developed using commercially available n-BuLi as a precatalyst. This hydroamination reaction successfully afforded allenyl-substituted pyrrolidines with up to 95% yield. One of the resulting allenyl pyrrolidines was converted to the natural products irniine and irnidine in three steps.     

Chelating diamide based rate enhancement of intramolecular alkene hydroaminations catalyzed by a neutral Sc(III) complex

[reaction: see text] Neutral scandium amido complexes are viable catalysts for intramolecular alkene hydroamination. Catalytic activity is strongly coupled to the electronic character of the Sc(III) ligand environment with chelating diamide coordination providing a precatalyst possessing substantially improved activity and superb distereoselectivity in the synthesis of trans-2,5-disubstituted pyrrolidines.     

TiCl4/t-BuNH2 as the sole catalyst for a hydroamination-based Fischer indole synthesis

A system comprising TiCl₄ and t-BuNH₂ acts as a catalyst for highly regioselective hydroamination reactions of alkynes using hydrazines and at the same time a Lewis acid in the transformation of the generated hydrazones into indole derivatives, while a 1,3-diyne is converted to pyrroles using the same precatalyst.     

A highly reactive titanium precatalyst for intramolecular hydroamination reactions

[reaction: see text]. Tetrakisamido titanium complexes are significantly more active than Cp2TiMe2 (1) in the intramolecular hydroamination of aminoalkynes and aminoallenes. In the latter case, the regioselectivity of the transformation depends on the nature of the precatalyst, yielding the most selective and reactive catalysis with the bis(sulfonamido) complex 11.     

Organolanthanide-mediated intermolecular hydroamination of 1,3-dienes: mechanistic insights from a computational exploration of diverse mechanistic pathways for the stereoselective hydroamination of 1,3-butadiene with a primary amine supported by an ansa-neodymocene-based catalyst

The complete catalytic reaction course for the organolanthanide-mediated intermolecular hydroamination of 1,3-butadiene and n-propylamine by an archetypical [Me2Si(eta5-Me4C5)2NdCH(SiMe3)2] precatalyst was critically scrutinized by employing a reliable gradient-corrected DFT method. A free-energy profile of the overall reaction is presented that is based on the thorough characterization of all crucial elementary steps for a tentative catalytic cycle. A computationally verified, revised mechanistic scenario is proposed which is consistent with the experimentally derived empirical rate law and accounts for crucial experimental observations. It involves kinetically mobile reactant association/dissociation equilibria and facile, reversible intermolecular diene insertion into the Nd-amido bond, linked to turnover-limiting protonolysis of the eta3-butenyl-Nd functionality. The computationally predicted effective kinetics (Delta(tot) = 11.3 kcal mol(-1), Delta(tot) = -35.7 e.u.) are in reasonably good agreement with experimental data for the thoroughly studied hydroamination of alkynes. The thermodynamic and kinetic factors that determine the almost complete regio- and stereoselectivity of the mechanistically diverse intermolecular 1,3-diene hydroamination have been unraveled. The present computational study complements experiments because it allows, first, a more detailed understanding and a consistent rationalization of the experimental results for the hydroamination of 1,3-dienes and primary amines and, second, enhances the insights into general mechanistic aspects of organolanthanide-mediated intermolecular hydroamination.     

Anti-Markovnikov intermolecular hydroamination: a bis(amidate) titanium precatalyst for the preparation of reactive aldimines

[reaction: see text] A bulky bis(N-2',6'-diisopropylphenyl(phenyl)-amidate)titanium-bis(diethylamido) complex was identified as a highly active and regioselective precatalyst for the anti-Markovnikov hydroamination of a wide range of terminal alkyl alkynes with alkylamines. This titanium complex was fully characterized, including its X-ray crystal structure. The reactive aldimine products generated have been further elaborated using one-pot procedures to give substituted amines, aldehydes, and the isoquinoline framework.     

Stereo- and regioselective gold-catalyzed hydroamination of internal alkynes with dialkylamines

We report the use of a P,N-ligand to support a gold complex as a state-of-the-art precatalyst for the stereoselective hydroamination of internal aryl alkynes with dialkylamines to afford E-enamine products. Substrates featuring a diverse range of functional groups on both the amine (ether, sulfide, N-Boc amine, fluoro, nitrile, nitro, alcohol, N-heterocycles, amide, ester, and carboxylic acid) and alkyne (ether, N-heterocycles, N-phthalimide amines, and silyl ethers) are accommodated with synthetically useful regioselectivity.     

Efficient intramolecular hydroamination of aminoalkynes catalyzed by a zirconium(IV) complex

The neutral zirconium(IV) bis(thiophosphinic amidate) complex was demonstrated to be an effective precatalyst for 5-exo-, 6-exo-, and 7-exo-dig intramolecular hydroamination of aminoalkynes, producing the cyclic imines in excellent yields (92-98%).     

Intermolecular hydroamination of oxygen-substituted allenes. New routes for the synthesis of N,O-chelated zirconium and titanium amido complexes

Intermolecular hydroamination of heteroatom-substituted allenes with a bulky arylamine was carried out using a bis(amidate) bis(amido) titanium(IV) complex (1) as a precatalyst. The reaction of 2,6-dimethylaniline with oxygen-substituted allene 2c or 2d in the presence of complex 1 gives the ketimine regioisomer as the exclusive product. Reduction of such ketimine products resulted in the formation of amino ethers that were further employed as proligands for the formation of N,O-chelating five-membered titana- and zirconacycles. Such sterically demanding N,O-chelating ligands result in the high-yielding preparation of mono-ligated products. Solid-state molecular structures of all the complexes revealed distorted trigonal bipyramidal geometry about the metal centers, with a dative bond between the metal and the oxygen donor atom. These new complexes obtained using hydroamination as the key-step in ligand preparation were also shown to be useful cyclohydroamination precatalysts in their own right.     

Well‐Defined Four‐Coordinate Iron(II) Complexes For Intramolecular Hydroamination of Primary Aliphatic Alkenylamines

Despite the growing interest in iron catalysis and hydroamination reactions, iron‐catalyzed hydroamination of unprotected primary aliphatic amines and unactivated alkenes has not been reported to date. Herein, a novel well‐defined four‐coordinate β‐diketiminatoiron(II) alkyl complex is shown to be an excellent precatalyst for the highly selective cyclohydroamination of primary aliphatic alkenylamines at mild temperatures (70–90 °C). Both empirical kinetic analyses and the reactivity of an isolated iron(II) amidoalkene dimer, [LFe(NHCH₂CPh₂CH₂CH?CH₂)]₂ favor a stepwise σ‐insertive mechanism that entails migratory insertion of the pendant alkene into an iron–amido bond associated with a rate‐determining aminolysis step.     

anti‐Markovnikov Hydroamination of Alkenes Catalyzed by a Two‐Component Organic Photoredox System: Direct Access to Phenethylamine Derivatives

Disclosed herein is a general catalytic system for the intermolecular anti‐Markovnikov hydroamination of alkenes. By using an organocatalytic photoredox system, α‐ and β‐substituted styrenes as well as aliphatic alkenes undergo anti‐Markovnikov hydroamination. Heterocyclic amines were also successfully employed as nitrogen nucleophiles, thus providing a direct route to heterocyclic motifs common in medicinal agents.     

Theoretical study on the mechanism of the reaction for alkene hydroaminations catalyzed by chiral aldehyde

Alkene hydroamination catalyzed by chiral aldehyde relying only on temporary intramolecularity is a new concept reaction. In this article, the reaction mechanism was investigated using density functional theory. The calculation results show that: (1) The reaction can be divided into two parts. The first part is a dehydration process involving a hemiaminal formation. The nitrone catalyst forms through rapid intermolecular nucleophilic addition of benzylhydroxylamine to chiral aldehyde precatalyst. The second part is a catalytic cycle, which involves an aminal formation—hydroamination—ring opening—product release process. (2) There are four enantioselective pathways related to the products of S and R configurations. Enantioselectivity is attributed to the different forming ways of a planar five‐membered ring. The preferred pathways for the S‐configuration product ( S3 ) and R‐configuration product ( R3 ) are confirmed. © 2013 Wiley Periodicals, Inc.     

Computational insight into a gold(I) N-heterocyclic carbene mediated alkyne hydroamination reaction

A gold(I) N-heterocyclic carbene (NHC) complex mediated hydroamination of an alkyne has been modeled using density functional theory (DFT) study. In this regard, alkyne and amine coordination pathways have been investigated for the hydroamination reaction between two representative substrates, namely, MeC≡CH and PhNH(2), catalyzed by a gold(I) NHC based (NHC)AuCl-type precatalyst, namely, [1,3-dimethylimidazol-2-ylidene]gold chloride. The amine coordination pathway displayed a lower activation barrier than the alkyne coordination pathway. The catalytic cycle is proposed to proceed via a crucial proton-transfer step occurring between the intermediates [(NHC)AuCH═CMeNH(2)Ph](+) (D) and [(NHC)Au(PhNHMeC═CH(2))](+) (E), the activation barrier of which was found to be significantly reduced by a proton relay mechanism process assisted by the presence of any adventitious H(2)O molecule or even by any of the reacting PhNH(2) substrates. The final hydroaminated enamine product, PhNHMeC═CH(2), was further seen to be stabilized in its tautomeric imine form PhN═CMe(2).     

Intramolecular hydroamination/cyclisation of aminoallenes mediated by a cationic zirconocene catalyst: a computational mechanistic study

The complete sequence of steps of a tentative catalytic cycle for intramolecular hydroamination/cyclisation (IHC) of 4,5-hexadien-1-ylamine (1) by a prototypical cationic [Cp(2)ZrCH(3)](+) zirconocene precatalyst (2) has been examined by employing a gradient-corrected DFT method. The predicted smooth overall reaction energy profile is consistent with the available experimental data, thereby providing further confidence in the proposed mechanism. Following activation of the precatalyst by protonolytic cleavage of the Zr-Me bond, the catalytically active amidoallene-Zr complex undergoes addition of an allenic C[double bond, length as m-dash]C linkage across the Zr-N sigma-bond. The alternative exo- and endocyclic pathways show similar probabilities for the sterically less encumbered reactants {1 + 2} investigated herein. However, steric factors are expected to exert control on the regioselectivity of ring closure. On the other hand, the metathesis-type transition states for subsequent protonolysis are indicated to be less sensitive to steric demands. Formation of the six-membered azacycle-Zr intermediate through intramolecular C[double bond, length as m-dash]C insertion into the Zr-N sigma-bond is predicted to be turnover limiting. The factors that govern the regioselectivity of the aminoallene IHC have been elucidated.     

Heteroleptic Alkyl and Amide Iminoanilide Alkaline Earth and Divalent Rare Earth Complexes for the Catalysis of Hydrophosphination and (Cyclo)Hydroamination Reactions

[{N^N}M(X)(thf)_n] alkyl (X=CH(SiMe₃)₂) and amide (X=N(SiMe₃)₂) complexes of alkaline earths (M=Ca, Sr, Ba) and divalent rare earths (Yb^II and Eu^II) bearing an iminoanilide ligand ({N^N}^?) are presented. Remarkably, these complexes proved to be kinetically stable in solution. X‐ray diffraction studies allowed us to establish size–structure trends. Except for one case of oxidation with [{N^N}Yb^II{N(SiMe₃)₂}(thf)], all these complexes are stable under the catalytic conditions and constitute effective precatalysts for the cyclohydroamination of terminal aminoalkenes and the intermolecular hydroamination and intermolecular hydrophosphination of activated alkenes. Metals with equal sizes across alkaline earth and rare earth families display almost identical apparent catalytic activity and selectivity. Hydrocarbyl complexes are much better catalyst precursors than their amido analogues. In the case of cyclohydroamination, the apparent activity decreases with metal size: Ca>Sr>Ba, and the kinetic rate law agrees with R_CHA=k[precatalyst]¹[aminoalkene]¹. The intermolecular hydroamination and hydrophosphination of styrene are anti‐Markovnikov regiospecific. In both cases, the apparent activity increases with the ionic radius (Ca<Sr<Ba) but the rate laws are different, and obey R_HA=k[styrene]¹[amine]¹[precatalyst]¹ and R_HP=k[styrene]¹[HPPh₂]⁰[precatalyst]¹, respectively. Mechanisms compatible with the rate laws and kinetic isotopic effects are proposed. [{N^N}Ba{N(SiMe₃)₂}(thf)₂] ( 3 ) and [{N^N}Ba{CH(SiMe₃)₂}(thf)₂] ( 10 ) are the first efficient Ba‐based precatalysts for intermolecular hydroamination and hydrophosphination, and display activity values that are above those reported so far. The potential of the precatalysts for C? N and C? P bond formation is detailed and a rare cyclohydroamination–intermolecular hydroamination “domino” sequence is presented.     

Gold-catalyzed hydroamination/cycloisomerization reaction of 1,6-enynes

An efficient Au(I) catalytic system is described for the hydroamination/cycloisomerization reaction of functionalized 1,6-enynes. The reaction leads to carbo- and heterocyclic amino derivatives in good to excellent yields. The cyclizations were conducted in the presence of PPh(3)AuCl/AgSbF(6) catalyst in THF or dioxane at room temperature. The use of allyloxycarbonyl carbamate has allowed the formation of free amino derivatives via sequential Au- and Pd-catalyzed reactions.     

C2-symmetric bis(oxazolinato)lanthanide catalysts for enantioselective intramolecular hydroamination/cyclization

C(2)-symmetric bis(oxazolinato)lanthanide complexes of the type [(4R,5S)-Ph(2)Box]La[N(TMS)(2)](2), [(4S,5R)-Ar(2)Box]La[N(TMS)(2)](2), and [(4S)-Ph-5,5-Me(2)Box]La[N(TMS)(2)](2) (Box = 2,2'-bis(2-oxazoline)methylenyl; Ar = 4-tert-butylphenyl, 1-naphthyl; TMS = SiMe(3)) serve as precatalysts for the efficient enantioselective intramolecular hydroamination/cyclization of aminoalkenes and aminodienes. These new catalyst systems are conveniently generated in situ from the known metal precursors Ln[N(TMS)(2)](3) or Ln[CH(TMS)(2)](3) (Ln = La, Nd, Sm, Y, Lu) and 1.2 equiv of commercially available or readily prepared bis(oxazoline) ligands such as (4R,5S)-Ph(2)BoxH, (4S,5R)-Ar(2)BoxH, and (4S)-Ph-5,5-Me(2)BoxH. The X-ray crystal structure of [(4S)-(t)BuBox]Lu[CH(TMS)(2)](2) provides insight into the structure of the in situ generated precatalyst species. Lanthanides having the largest ionic radii exhibit the highest turnover frequencies as well as enantioselectivities. Reaction rates maximize near 1:1 BoxH:Ln ratio (ligand acceleration); however, increasing the ratio to 2:1 BoxH:Ln decreases the reaction rate, while affording enantiomeric excesses similar to the 1:1 BoxH:Ln case. A screening study of bis(oxazoline) ligands reveals that aryl stereodirecting groups at the oxazoline ring 4 position and additional substitution (geminal dimethyl or aryl) at the 5 position are crucial for high turnover frequencies and good enantioselectivities. The optimized precatalyst, in situ generated [(4R,5S)-Ph(2)Box]La[N(TMS)(2)](2), exhibits good rates and enantioselectivities, comparable to or greater than those achieved with chiral C(1)-symmetric organolanthanocene catalysts, even for poorly responsive substrates (up to 67% ee at 23 degrees C). Kinetic studies reveal that hydroamination rates are zero order in [amine substrate] and first order in [catalyst], implicating the same general mechanism for organolanthanide-catalyzed hydroamination/cyclizations (intramolecular turnover-limiting olefin insertion followed by the rapid protonolysis of an Ln-C bond by amine substrate) and implying that the active catalytic species is monomeric.     

Intramolecular enantioselective hydroamination catalyzed by rare earth binaphthylamides

Asymmetric intramolecular hydroamination reaction is a stately way to prepare chiral nitrogen-containing heterocyclic compounds. We report in this account our personal contribution in this field with the synthesis of chiral amido rare-earth complexes. A new family of structurally defined heterobimetallic rare earth lithium ate complexes based on N-substituted binaphthylamido ligands was discovered that promoted the hydroamination/cyclization of aminoolefins with up to 87% ee.Neutral rare earth amido and amido alkyl complexes could also be prepared and led to very active species. A more simple and reliable synthetic procedure was discovered towards the preparation of heterobimetallic rare earth amido alkyl ate complexes. They proved to be also active and enantioselective catalysts, as a good compromise between efficiency and practicability issues.     

Nickel-catalyzed amination of aryl sulfamates and carbamates using an air-stable precatalyst

A facile nickel-catalyzed method to achieve the amination of synthetically useful aryl sulfamates and carbamates is reported. Contrary to most Ni-catalyzed amination reactions, this user-friendly approach relies on an air-stable Ni(II) precatalyst, which, when employed with a mild reducing agent, efficiently delivers aminated products in good to excellent yields. The scope of the method is broad with respect to both coupling partners and includes heterocyclic substrates.