A new homogeneous zinc complex with increased reactivity for the intramolecular hydroamination of alkenes

The new zinc compound N-cyclohexyl-2-(cyclohexylamino)troponiminate zinc methyl, [(Cy)2ATI]ZnMe, was synthesized and showed a superior reactivity in the intramolecular hydroamination reaction of non-activated alkenes compared to previously reported homogeneous zinc complexes.     

Intramolecular hydroamination with homogeneous zinc catalysts: evaluation of substituent effects in N,N'-disubstituted aminotroponiminate zinc complexes

A series of symmetrical and unsymmetrical N,N'-disubstituted aminotroponimines (ATIHs) have been prepared. Substituents ranging from linear to cyclic alkyl groups, chelating ethers, and aryl groups were employed. The corresponding aminotroponiminate zinc complexes were then synthesized and characterized by a number of techniques, including by X-ray crystallography. Herein we report on the investigations into their activity in the intramolecular hydroamination of nonactivated alkenes. We also demonstrate that complexes bearing ligands with cyclic alkyl groups show superior activity in a number of selected reactions with functionalized aminoalkenes.     

Halogenation of carbon substrates for increased reactivity with alkenes

Carbon substrates are readily functionalized with alkene-containing molecules via an ultraviolet-light-catalyzed reaction, resulting in the formation of a carbon-carbon bond with the surface. This reaction is typically performed on hydrogen-terminated carbon substrates, limiting its utility as alkene molecules with low electron affinities do not readily attach to this surface. Recently, a wet-chemical method for preparing bromine- and chlorine-terminated carbon substrates has been developed. Replacing the terminal hydrogen atoms with a halogen analog increases the surface's reactivity with alkene-containing molecules, affording a means of modifying the carbon substrate with the alkene molecules that do not readily attach to the hydrogen-terminated surface and with a greatly reduced reaction time.     

An in situ generated samarium complex as a practical catalyst for the efficient intramolecular hydroamination of non-activated alkenes

Mixing SmI₂ and NaN(TMS)₂ generates in situ an efficient catalyst that promotes the intramolecular hydroamination of non-activated olefins. A wide range of aminoolefins can be cyclised smoothly using this simple protocol. Mechanistic studies led to the identification of the putative active catalyst.     

Organolanthanide-catalyzed intramolecular hydroamination/cyclization of amines tethered to 1,2-disubstituted alkenes

[reaction: see text] This contribution reports the organolanthanide-catalyzed intramolecular hydroamination/cyclization of amines tethered to 1,2-disubstituted alkenes to afford the corresponding mono- and disubstituted pyrrolidines and piperidines by using coordinatively unsaturated complexes of the type (eta(5)-Me(5)C(5))(2)LnCH(TMS)(2) (Ln = La, Sm), [Me(2)Si(eta(5)-Me(4)C(5))(2)]NdCH(TMS)(2), [Et(2)Si(eta(5)-Me(4)C(5))(eta(5)-C(5)H(4))]NdCH(TMS)(2), and [Me(2)Si(eta(5)-Me(4)C(5))((t)()BuN)]LnE(TMS)(2) (Ln = Sm, Y, Yb, Lu; E = N, CH) as precatalysts. [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]LnE(TMS)(2) mediates intramolecular hydroamination/cyclization of sterically demanding amino-olefins to afford disubstituted pyrrolidines in high diastereoselectivity (trans/cis = 16/1) and in good to excellent yield.     

Intermolecular hydroamination and hydroarylation reactions of alkenes in ionic liquids

Intermolecular hydroamination or hydroarylation reactions of norbornene and cyclohexadiene performed with catalytic amounts of Brönsted or Lewis acid in ionic liquids were found to provide higher selectivity and yields than those performed in classical organic solvents. The ionic liquid increases the acidity of the media and stabilizes ionic intermediates through the formation of supramolecular aggregates.     

Catalytic, enantioselective intramolecular hydroamination of primary amines tethered to di- and trisubstituted alkenes

The in situ preparation of chiral amido alkyl ate yttrium complexes from an array of chiral N-benzyl-like-substituted binaphthyldiamines is reported. These chiral heteroleptic complexes are shown to be efficient catalysts for the enantioselective intramolecular hydroamination of primary amines tethered to sterically demanding alkenes at high reaction temperatures. Fine tuning of their chiral environment allowed up to 77% ee to be reached for the cyclization of aminoalkenes bearing 1,2-dialkyl-substituted carbon-carbon double bonds. These chiral complexes also demonstrate the ability to promote the cyclization of amine-tethered trisubstituted alkenes in up to 55% ee, as the first report of the formation of enantioenriched quaternary centers by an hydroamination reaction.     

An electron-excessive nitrosyl complex: reactivity of a ligand-centered radical leading to coordinated HNO

The reaction of RuHCl(CO)L(2) (L = P(i)Pr(3)) with NO initially forms a 1:1 adduct, shown by DFT calculations and EPR spectroscopy (including the RuD isotopomer) to contain a bent ( 90 degree angle Ru-N-O = 143.9 degrees ) nitrosyl where the majority of the spin density is on the nitrosyl nitrogen. This radical adduct transforms further to give equimolar RuCl(NO)(CO)L(2) and RuHCl(HNO)(CO)L(2), the latter with hydride trans to the nitroxyl ligand HN=O. This is the first observation of the synthesis of coordinated HNO from NO itself. DFT calculations lead to the proposal that this H-atom transfer is effected by free NO, and the lifetime of RuHCl(HNO)(CO)L(2) is indeed qualitatively dependent on the presence of free NO.     

Mechanistic studies of a palladium-catalyzed intramolecular hydroamination of unactivated alkenes: protonolysis of a stable palladium alkyl complex is the turnover-limiting step

Mechanistic studies of the intramolecular hydroamination of unactivated aminoalkenes catalyzed by a dicationic [bis(diphenylphosphinomethyl)pyridine]palladium complex highlight the important role that protonolysis plays in this reaction. Coordination of the aminoalkene substrate to this complex activates the alkene toward intramolecular nucleophilic attack to form a dicationic palladium alkyl complex (6). A stable monocationic palladium alkyl complex (7) was isolated by in situ deprotonation of 6 with mild base, and its structure was confirmed by X-ray crystallography. Complex 7 reacted rapidly with a variety of strong acids to undergo protonolysis, resulting in formation of hydroamination product 3 and regenerating the active catalyst. Evidence that formation of the palladium alkyl complex is reversible under the catalytic conditions was obtained from observation of the protonolysis at low temperature. During the course of all catalytic reactions, the resting state of the catalyst was palladium alkyl complex 7, indicating that protonolysis of the Pd-C bond was the turnover-limiting step. Kinetic studies reveal an unusual inverse dependence of the reaction rate on the concentration of the aminoalkene substrate. This effect can be accurately explained by a model in which the carbamate protecting group of the aminoalkene acts as a Br?nsted base to remove free protons from the catalytic cycle and thereby inhibits the turnover-limiting protonolysis step. Formation of a 2:1 complex (12) between the carbamate and the proton is most consistent with the kinetic data.     

Ruthenium-catalyzed addition of sulfenamides to alkynes leading to selective synthesis of polyfunctional alkenes

Sulfenamides smoothly add to alkynes by [RuCl₂(CO)₃]₂ or Ru₃(CO)₁₂ catalyst to give the corresponding polyfunctional alkenes in high yield with high regio- and stereoselectivity (Z 100%).     

Theoretical study of the methylic reactivity of substituted alkenes

A PM3/UHF study of the methylic reactivity of a series of about fifty alkenes was carried out. Several MP2/6-31G^** ab initio calculations were made for comparison. The semi-empirical method of calculation is proven to give good estimates of the reactivity under consideration. The computations brought to light the reactivity enhancement of alkenes when substituted on the same carbon of the double bond, whereas a lessening is observed when both carbons are substituted. An interpretation in terms of deformation (DEF) and interaction (INT) energies is made. Contrarily to phenyl, the vinyl group improves notably the reactivity of methylated and chlorinated mono or disubstituted alkenes. The prediction is made for the reactivity of more than fifteen compounds which were not studied experimentally.     

The hydroamination of alkenes with sulfonamides catalyzed by the recyclable silica gel supported triflic acid

The vast applications of triflic acid (TfOH) in catalysis are severely limited by its corrosive and fuming properties. Immobilization of TfOH on silica gel well solves these problems and affords efficient recovery and reusability of TfOH. Two types of supported TfOH, the prepared silica gel supported TfOH and the in situ silica gel adsorbed TfOH, both exhibit good catalytic activity and reusability in the hydroamination of alkene with sulfonamide. The in situ silica gel adsorbed catalyst has been used for 5 runs with maintained reactivities and yields, which are superior to the performance of the prepared silica gel supported TfOH. For a series of alkenes and various sulfonamides, the heterogeneous hydroamination reactions catalyzed by both types of silica gel supported TfOH to afford similar moderate to excellent yields.     

Mechanism of the intramolecular hydroamination of alkenes catalyzed by neutral indenyltitanium complexes: a DFT study

Three mechanistic pathways for the [Ind(2)TiMe(2)]-catalyzed intramolecular hydroamination of alkenes have been investigated by employing density functional theory calculations on the possible intermediates and transition states. The results indicate that the reaction cycle proceeds via a Ti-imido-amido complex as the catalytically active species. However, at the moment, the question as to whether this imido-amido complex is involved in a [2+2]-cycloaddition with the alkene or a newly proposed insertion of the alkene into a Ti--N single bond cannot be answered; the calculated barriers of both the insertion mechanism and the [2+2]-cycloaddition mechanism are similar (143 vs. 136 kJ mol(-1)), and both pathways are in accordance with the experimentally observed rate law (first-order dependence on the aminoalkene concentration). Interestingly, the newly proposed insertion mechanism that takes place by an insertion of the alkene moiety into the Ti--N single bond of an imido-amido complex seems to be much more likely than a mechanism that involves an alkene insertion into a Ti--N single bond of a corresponding trisamide. The latter mechanism, which has been proposed in analogy to rare-earth-metal-catalyzed hydroamination reactions, can be ruled out for two reasons: a surprisingly high activation barrier (164 kJ mol(-1)) and the fact that the rate-limiting insertion step is independent of the aminoalkene concentration. This is in sharp contrast to the experimental findings for indenyltitanium catalysts.     

Intermolecular, catalytic asymmetric hydroamination of bicyclic alkenes and dienes in high yield and enantioselectivity

A set of catalytic, intermolecular hydroaminations of strained bicyclic olefins and dienes are reported that occur in both high yield and high enantioselectivity. These reactions occur with a catalyst generated from [Ir(cyclooctene)Cl]2, sterically hindered and electron-rich derivatives of the Segphos and BIPHEP family of ligands, and a soluble base. This system catalyzes the addition of various anilines to norbornene, norbornadiene, and other bicyclic olefins. The products from addition of p-anisidine can be transformed to BOC-protected norbornylamine and to substituted cyclopentanes in nearly enantiopure form. Mechanistic studies show that addition of aniline-d2 occurs in a syn fashion and suggest that the catalytic cycle comprises oxidative addition of aniline to form a bis-anilide hydride complex, followed by migratory insertion of olefin and reductive elimination of product in a series of steps involving iridium complexes containing ancillary bisphosphine and arylamide ligands.     

Gold(III)-catalyzed double hydroamination of o-alkynylaniline with terminal alkynes leading to N-vinylindoles

A highly efficient double-hydroamination reaction of o-alkynylanilines with terminal alkynes leading to N-alkenylindoles was developed by using gold(III) as a catalyst under neat conditions. [reaction: see text].