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.     

Intramolecular alkyne hydroalkoxylation and hydroamination catalyzed by iridium hydrides

[reaction: see text] Iridium(III) hydrides prove to be air-stable active catalysts for intramolecular hydroalkoxylation and hydroamination of internal alkynes with proximate nucleophiles. The cyclization follows highly selective 6-endo-dig regiochemistry when regioselectivity is an issue.     

Intramolecular hydroamination of aminoalkenes catalyzed by a cationic zirconium complex

A new cationic [N(-)O(-)S]zirconium complex (cat.) was developed to be an excellent catalyst for the intramolecular hydroamination of aminoalkenes with a large substrate scope from terminal alkenes to internal alkenes, and primary amines to secondary amines. The catalyst system can also tolerate various functional groups and perform sequential hydroamination of primary aminodienes.     

Intramolecular hydroamination of alkynes catalyzed by Pd(PPh3)4/triphenylphosphine under neutral conditions

The intramolecular hydroamination of alkynes tethered with amino group 1 in the presence of catalytic amounts of Pd(PPh3)4 and PPh3 in benzene at 100 degrees C proceeded smoothly without the use of any additional acid source to afford five- and six-membered nitrogen heterocycles 2 in good to excellent yields. A compulsory addition of carboxylic acid as a cocatalyst was not needed, and the reaction could be carried out under essentially neutral conditions.     

Intramolecular hydroamination of 6-aminohex-1-yne catalyzed by Lewis acidic rhenium(I) carbonyl complexes

With the aim to determine the effect of Lewis acidity of rhenium(I) carbonyl complexes on their catalytic properties, and to develop more efficient catalysts based on Re(I) carbonyl systems, a series of rhenium(I) carbonyl triflate complexes with various degrees of Lewis acidity was investigated. Pyridine-substituted bromo tricarbonyl rhenium(I) complexes of the type fac-[ReBr(CO)₃L₂] (L = py-Cl, py, py-Me and py-NMe₂) were synthesized from [ReBr(CO)₅] using trimethylamine N-oxide (TMNO) as decarbonylating agent. The complexes [ReBr(CO)₅] and fac-[ReBr(CO)₃L₂] were then reacted with silver triflate to yield the complexes [Re(CF₃SO₃)(CO)₅] and fac-[Re(CF₃SO₃)(CO)₃L₂]. The synthesis and characterization of these complexes and their application in the catalysis of the cyclization of 6-aminohex-1-yne are discussed. The crystal structure of [Re(CF₃SO₃)(CO)₃(py)₂] is also presented.     

Intramolecular hydroamination/cyclization of aminoalkenes catalyzed by diamidobinaphthyl magnesium- and zinc-complexes

Reaction of 2 equiv of n-Bu₂Mg and Et₂Zn with the chiral l-proline-derived axial chiral tetraamines (S,S,S)-1 and (R,S,S)-1 gave the chiral bimetallic complexes [M₂{(S,S,S)-DABN(MeProline)₂}{R}₂] (M=Mg, R=n-Bu ((S,S,S)-2); M=Zn, R=Et ((S,S,S)-3)) and [M₂{(R,S,S)-DABN(MeProline)₂}{R}₂] (M=Mg, R=n-Bu ((R,S,S)-2)); M=Zn, R=Et ((R,S,S)-3)). The magnesium complexes showed moderate to high catalytic activity in the intramolecular hydroamination/cyclization of aminoalkenes, though enantiomeric excess was limited to 14% ee due to protolytic ligand exchange processes. The zinc complexes were less reactive and generally required higher reaction temperatures of 60-100 °C, but achieved slightly higher enantiomeric excess of up to 29% ee.     

Room temperature hydroamination of N-alkenyl ureas catalyzed by a gold(i) N-heterocyclic carbene complex

[Structure: see text] Treatment of an N-4-pentenyl or N-5-hexenyl urea with a catalytic 1:1 mixture of a gold(I) N,N-diaryl imidazol-2-ylidine complex and AgOTf at or near room temperature leads to intramolecular exo-hydroamination to form the corresponding nitrogen heterocycle in excellent yield.     

Total synthesis of (-)-quinocarcin by gold(i)-catalyzed regioselective hydroamination

In control: The novel and enantioselective total synthesis of (-)-quinocarcin includes the highly stereoselective preparation of the 2,5-cis-pyrrolidine by intramolecular amination, a selective substrate-controlled 6-endo-dig intramolecular alkyne hydroamination with a cationic Au(I) catalyst, and Lewis-acid-mediated ring-opening/halogenation sequence.     

Intermolecular hydroamination of allenes with N-unsubstituted carbamates catalyzed by a gold(I) N-heterocyclic carbene complex

Reaction of 2,3-pentadienyl benzoate with benzyl carbamate catalyzed by a 1:1 mixture of (NHC)AuCl and AgOTf in dioxane at 23 degrees C for 5 h led to isolation of (E)-4-(benzyloxycarbonylamino)-2-pentenyl benzoate in 84% yield as a single regio- and diastereomer. Gold(I)-catalyzed hydroamination was effective for a number of N-unsubstituted carbamates and a range of substituted allenes.     

Intramolecular hydroamination/cyclization of aminoalkenes catalyzed by Ln[N(SiMe(3))(2)](3) grafted onto periodic mesoporous silicas

Homoleptic rare-earth metal silylamide complexes Ln[N(SiMe(3))(2)](3) (Ln = Y, La, Nd) were grafted onto a series of partially dehydroxylated periodic mesoporous silica (PMS) supports, SBA-15(-500) (d(p) = 7.9 nm), SBA-15LP(-500) (d(p) = 16.6 nm), and MCM-41(-500) (d(p) = 4.1 nm). The hybrid materials Ln[N(SiMe(3))(2)](3)@PMS efficiently catalyze the intramolecular hydroamination/cyclization reaction of 2,2-dimethyl-4-penten-1-amine. Under the prevailing slurry conditions the metal size (Y > La > Nd), the pore size, and the particle morphology affect the catalytic performance. Material Y[N(SiMe(3))(2)](3)@SBA-15LP(-500) displayed the highest activity (TOF = up to 420 h(-1) at 60 °C), with the extralarge pores minimizing restrictive product inhibition and substrate diffusion effects. The catalytic activity of Y[N(SiMe(3))(2)](3)@SBA-15LP(-500) is found to be much higher than that of the molecular counterpart (TOF = up to 54 h(-1)), and its recyclability is demonstrated.     

Visual detection of silver(I) ions by a chromogenic reaction catalyzed by gold nanoparticles

We report on a novel method for visual detection silver(I) ion. It is based on the finding that Ag(I) ions are rapidly reduced by hydroquinone to form a shell of silver on the surface of gold nanoparticles (AuNPs) which act as catalysts for this reaction. This leads to a color change from red to yellow which can be seen with bare eyes. This scheme is sensitive and highly specific for Ag(I) ions. The detection limits are 5 μM for visual inspection and 1 μM for photometric readout, respectively. The method was successfully applied to the determination of Ag(I) ions in spiked lake water and soil.

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.     

Intramolecular hydroamination of unactived olefins with Ti(NMe2)4 as a precatalyst

Commercially available Ti(NMe(2))(4) has been used effectively as a precatalyst in a facile protocol for the intramolecular hydroamination of aminoalkenes to yield pyrrolidine and piperidine heterocyclic products with isolated yields up to 92%. Geminally substituted substrates display the highest reactivity. This precatalyst is also effective for the hydroamination of activated internal alkenes, providing access to more complex heterocyclic target molecules.     

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%).     

Reaction of hydrosilanes with alkynes catalyzed by gold nanoparticles supported on TiO2

Gold nanoparticles supported on TiO₂ (0.8–1.4 mol %) catalyze the β-(E) regioselective hydrosilylation of a variety of functionalized terminal alkynes with alkylhydrosilanes in 1,2-dichloroethane (70 °C). The product yields are excellent, and the reaction times relatively short, while almost equimolar amounts of alkynes and hydrosilanes can be used. Minor side-products in up to 35% relative yield of cis-oxidative (dehydrogenative) disilylation, an unprecedented reaction pathway, are formed in the cases of the less hindered hydrosilanes and alkynes. Triethoxysilane reacts faster and affords apart from β-(E) addition products, minor α-hydrosilylation regio-isomers in upto 15% relative yield. Internal alkynes are generally less reactive or even unreactive. It is proposed that cationic Au(I) species stabilized by the support are the reactive catalytic sites, forming in the presence of hydrosilanes either silyl–Au(III)–H (hydrosilylation pathway) or Au(III)–disilyl species (dehydrogenative disilylation pathway). Regarding the mechanism of hydrosilylation, kinetic experiments are in agreement with silyl carbometallation of the triple bond in the rate determining step of the reaction.     

Partial oxidations with NO(2) catalyzed by large gold particles

Large gold particles catalyze alkene epoxidation by NO(2) under mild conditions, oxygen adatoms being the likely active species.