Bicyclic Alkenes Research Articles

Cationic Iridium-Catalyzed Asymmetric Decarbonylative Aryl Addition of Aromatic Aldehydes to Bicyclic Alkenes.

We report an unprecedented catalytic protocol for the enantioselective decarbonylative transformation of aryl aldehydes. In this process, the decarbonylation of aldehydes catalyzed by chiral iridium complexes enabled the formation of asymmetric C-C bonds through the formation of an aryl-iridium intermediate. The decarbonylative aryl addition to bicyclic alkenes was fluidly performed without a stoichiometric aryl-metal reagent, such as aryl boronic acid, with a cationic iridium complex generated in situ from Ir(cod)2 (BArF 4 ) and the sulfur-linked bis(phosphoramidite) ligand ((R,R)-S-Me-BIPAM). This reaction has broad functional group compatibility, and no waste is generated, except carbon monoxide.

Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path.

Copolymerization of ethylene (E) with 5-vinyl-2-norbornene (VNB) catalyzed by ansa-metallocenes allows the precise control of essential polymeric properties such as comonomer incorporation, molecular weight (Mw), and polydispersity (Đ). Significant efforts have been devoted to synthesizing and developing novel catalysts, cocatalysts, and activators, although the fundamental elements of catalytic processes remain unclear. For example, it is questionable how polymeric catalysts are divided across dormant and active sites and how this distribution affects the order of monomers for the propagation rate, which widely vary in the literature. Furthermore, although the empirical correlation between the monomers and average Mw has been established in many systems, the fundamental processes of chain termination remain unknown. Furthermore, the involvement of ion-pairing in metallocene-catalyzed polymerization and the termination mechanisms are also contentious issues. In this study, we describe the use of a quenched-labeling technique based on acyl chloride to selectively quench the zirconium metal–polymeric bond, which can be used to study the kinetics, active site [Zr][C*] counting, copolymer microstructure, and molecular weight distribution (MWD) to determine the rate laws for chain initiation, chain propagation rate (Rp), propagation rate constant (kp) and chain termination. In addition, we also predict previously unknown chemical characteristics of E/bicyclic copolymerization processes, where either a cis-endocyclic double bond with steric properties or a vinyl exocyclic double bond affects the activity, i.e., [Zr]/[*C], (Rp) and (kp). All these properties require the implementation of a particular kinetic mechanism that assumes the low activity of the building copolymer chains incorporating a single ethylene/VNB unit, i.e., the Cp2Zr–C2H5 group, in the ethylene addition process in the Cp2Zr–C bond. Due to β-agostic stabilization, the Cp2Zr–C2H5 group exhibits a distinct feature. These effects were confirmed experimentally, such as the E/VNB co-polymer activity and VNB mol%, propagation rate decrease in the polymerization time (tp) of 120 s to 1800 s, crystalline properties, and significant increase in molecular weight. The active center [Zr]/[*C] fraction considerably increased in the initial (tp) 840 s, and subsequently tended to the steady stage of 33%, which is lower than previously reported E homo- and E/P copolymerization. The lower [C*]/[Zr] in both the early and stable stages, decrease in VNB mol%, and Rp with tp can be associated with the more significant fraction of Cp2Zr–CH2CH3-type dormant site by the β-agostic hydrogen interaction with the Cp2Zr metal. The tpversus RpE, RpVNB, kpE, kpVNB, and [Zr]/[C*] count could be fitted to a model that invokes deactivation of the growing polymer chains. In the case of the thermal behavior of the copolymers (melting temperature (Tm) and crystalline temperature (ΔHm)), Tm varied from 101 °C to 121 °C, while ΔHm varied from 9 to 16 (J g−1).

Copper-Catalyzed Hydroamination of Oxa- and Azabenzonorbornadienes with Pyrazoles.

An efficient and highly chemo- and stereoselective copper-catalyzed hydroamination of oxa- and azabenzonorbornadienes with various pyrazole derivatives is described. This catalytic process is promoted by the presence of N-heterocyclic carbene ligands and KOt-Bu under mild and simple reaction conditions, and allows for the direct synthesis of new and versatile functionalized oxa(aza)benzonorbornyl pyrazoles starting from readily available oxa(aza)bicyclic alkenes. The synthetic utility of this method was demonstrated by the transformation of the obtained products into pyrazolyl-substituted naphthalenes.

Non-Conventional Fluorescence and Cytotoxicity of Two Aliphatic Hyperbranched Polymer Dots Having Poly(amic acid) Structures: Implications for Labeling Nanodrug Carriers.

In this study, we used one-pot A2 + B3 polymerizations to synthesize two aliphatic + alicyclic polymer dots (PDs) having non-conjugated hyperbranched structures, employing two types of dianhydrides as the A2 components, possessing bridged bicyclic alkene (PD-BT) and non-alkene (PD-ET) units, and Jeffamine T403 polyetheramine (T403) as the B3 components. We prepared PD-ET from commercially available ethylenediaminetetraacetic dianhydride (EDTAD, A2) and T403 (B3) and PD-BT from bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA, A2) and T403 (B3). These two types of PDs possessed non-conjugated hyperbranched poly(amic acid) structures with terminal amino functional groups. PD-BT and PD-ET exhibited non-conventional fluorescence with emissions at 435 and 438 nm, respectively, and quantum yields of 12.8 and 14.0%, respectively. The fluorescence intensity of PD-ET was influenced by the pH, but PD-BT was less affected because of its rigid aliphatic bridged bicyclic structure. In aqueous solutions, the sizes of the PD-BT and PD-ET nanoparticles were 3–5 nm, and their net charges can be adjusted by varying the pH. These PDs were non-cytotoxic toward human MCF-7 breast cancer cells and human keratinocyte HaCaT cells at concentrations of 50 μg mL–1 for PD-BT and 500 μg mL–1 for PD-ET. Confocal microscopic bioimaging revealed that the PDs were located within the cells after treatment for 6 h. These PDs were easy to prepare, highly water-soluble, and possessed a large number of peripheral functional groups for further modification. Combined with their non-conventional fluorescence, they appear to have potential uses in bioimaging and as drug-labeling carriers.

Benzocarbazole Synthesis via Visible-Light-Accelerated Rh(III)-Catalyzed C-H Annulation of Aromatic Amines with Bicyclic Alkenes.

A visible-light-accelerated Rh(III)-catalyzed C-H annulation of aromatic amines with bicyclic alkenes for the synthesis of benzocarbazole derivatives was developed. In this approach, with the cooperation of rhodium catalysis and visible-light irradiation, various aromatic amines reacted with oxabicyclic alkenes and azabicyclic alkenes smoothly at room temperature, delivering the corresponding bridged oxa or aza tetrahydro benzocarbazoles in good to excellent yields. Moreover, a series of benzo[b]carbazoles were synthesized conveniently through further aromatization in one pot. The potential of this method was demonstrated via directing-group removal, derivatization, a scale-up reaction, and fluorescence investigations.

Palladium-Catalyzed Stereoselective Difunctionalization of Bicyclic Alkenes with Organoammonium Salts and Organoboronic Compounds.

A palladium-catalyzed difunctionalization of bicyclic alkenes with organoammonium salts and organoboronic compounds was reported. A wide range of functionalized cyclic products, including those bearing functional groups, were produced stereoselectively in good to excellent yields. The gram-scale experiment, one-pot operation, and synthetic application of β-borylated products further demonstrated the synthetic value of this new reaction in organic synthesis.

Palladium-Catalyzed Intermolecular Alkene Carboacylation via Ester C-O Bond Activation.

We report palladium-catalyzed intermolecular carboacylation of alkenes with ester electrophiles and tetraarylborate nucleophiles. Bicyclic alkenes react with a variety of pentafluorophenyl benzoate and alkanoate esters and sodium tetraarylborates to form ketone products in ≤99% yields. These reactions occur in the absence of a directing group and demonstrate esters are competent acyl electrophiles for intermolecular alkene carboacylation reactions.

Three-Component 1,2-Carboamidation of Bridged Bicyclic Alkenes via RhIII-Catalyzed Addition of C-H Bonds and Amidating Reagents.

A three-component method is described for the preparation of syn-1,2-disubstituted bridged bicyclic compounds. The reaction was demonstrated for readily available aromatic and heteroaromatic C-H bond substrates with tertiary and secondary amide, lactam, pyrazole, and triazole directing groups and a variety of bridged bicyclic alkenes, including norbornene, benzonorbornadiene, oxygen- and nitrogen-bridged analogs, and an unsaturated tropinone. A broad dioxazolone scope was also observed. The use of a chiral Cp-derived RhIII catalyst enables asymmetric synthesis of products.

Copper(I)-catalyzed [4 + 2] cycloaddition of aza-ortho-quinone methides with bicyclic alkenes.

A variety of tetrahydroquinoline-fused bicycles bearing multiple stereocenters are prepared in good yields with high diastereoselectivity through Cu2O-catalyzed [4 + 2] cycloaddition of aza-ortho-quinone methides (ao-QMs) with bicyclic alkenes. Mechanistic studies reveal that the Cu(i) catalyst not only promotes the formation of ao-QMs through a radical process by single electron transfer but also accelerates [4 + 2] cycloaddition. The reaction was easily performed on gram scale and the obtained tetrahydroquinoline-fused bicycles can be converted to diverse tetrahydroquinoline scaffolds.

Cobalt(III)‐Catalyzed Enantioselective Intermolecular Carboamination by C−H Functionalization

AbstractHigh‐valent cyclopentadienyl cobalt catalysis is a versatile tool for sustainable C−H bond functionalizations. To harness the full potential of this strategy, control of the stereoselectivity of these processes is necessary. Herein, we report highly enantioselective intermolecular carboaminations of alkenes through C−H activation of N‐phenoxyamides catalyzed by CoIII‐complexes equipped with chiral cyclopentadienyl (Cpx) ligands. The method converts widely available acrylates as well as bicyclic olefins into attractive enantioenriched isotyrosine derivatives as well as elaborated amino‐substituted bicyclic scaffolds under very mild conditions. The outlined reactivity is unique to the CpxCoIII complexes and is complementary to the reactivity of 4d‐ and 5d‐ precious‐metal catalysts.

Cobalt(III)-Catalyzed Enantioselective Intermolecular Carboamination by C-H Functionalization.

High-valent cyclopentadienyl cobalt catalysis is a versatile tool for sustainable C-H bond functionalizations. To harness the full potential of this strategy, control of the stereoselectivity of these processes is necessary. Herein, we report highly enantioselective intermolecular carboaminations of alkenes through C-H activation of N-phenoxyamides catalyzed by CoIII -complexes equipped with chiral cyclopentadienyl (Cpx ) ligands. The method converts widely available acrylates as well as bicyclic olefins into attractive enantioenriched isotyrosine derivatives as well as elaborated amino-substituted bicyclic scaffolds under very mild conditions. The outlined reactivity is unique to the Cpx CoIII complexes and is complementary to the reactivity of 4d- and 5d- precious-metal catalysts.

Remote γ-C(sp3)–H Alkylation of Aliphatic Carboxamides via an Unexpected Regiodetermining Pd Migration Process: Reaction Development and Mechanistic Study

In the presence of accessible β-C–H bonds, γ-C–H activation of saturated aliphatic carboxamides remains unresolved because β-C–H activation is kinetically favored. This is almost a dogma in the development of C–H activation reactions. Here we report a strategy to change this dogma, as we have found that a Pd-catalyzed, ligand-enabled remote γ-alkylation of saturated aliphatic carboxamides can be realized in the presence of more accessible β-C–H bonds by using strained bicyclic alkenes as the coupling partners. Density functional theory calculations and experiments suggested that the realization of the present reaction is due to a change in the regiodetermining step from commonly encountered irreversible C–H activations, which are reversible here, to an unexpected Pd migration process, which is regiodetermining. This is a new strategy to achieve γ-C–H activation, compared with the previous strategy, making γ-C–H activation both the turnover- and regiodetermining step.

Copper-catalyzed diastereoselective hydrothioetherification of oxa(aza)benzonorbornadienes.

A novel copper-catalyzed hydrothioetherification of oxa(aza)bicyclic alkenes with potassium thioacetate and aryl or alkyl iodides to synthesize unsymmetrical thioethers has been developed. Notably, the reaction with complete diastereoselectivity went through a syn-selective addition process to give exo-adducts. In addition, this protocol exhibited high efficiency and good functional group tolerance to afford the target thioethers in moderate to good yields. Based on the results of mechanistic investigations, a plausible mechanism was proposed.

Direct Access to Chiral Secondary Amides by Copper-Catalyzed Borylative Carboxamidation of Vinylarenes with Isocyanates.

A Cu-catalyzed borylative carboxamidation reaction has been developed using vinylarenes and isocyanates. Alkynes, branched 1,3-dienes, and bicyclic alkenes were also found to be competent coupling partners. Using a chiral phosphanamine ligand, an enantioselective variant of this transformation was developed, affording a set of α-chiral amides with unprecedented levels of enantioselectivity. The synthetic utility of the method was demonstrated through a series of representative stereoretentive postcatalytic derivatizations.

Benzene Alkylation with Cycloolefins under the Action of [Et3NH]+[Al2Cl7]− Ionic Liquid

Benzene alkylation with mono- and bicyclic olefins under the action of an inorganic ionic liquid [Et3NH]+[Al2Cl7]− with the formation of benzene cycloalkyl derivatives in 58–98% yield has been performed for the first time. It has been found that the increase in the olefin cycle size improves the selectivity with respect to monocycloalkyl derivatives.

Mn(III)acetate-mediated additions of active methylene compounds to bicyclic olefins: Synthesis of bicyclic olefin-fused dihydrofurans

Bicyclic alkenes such as benzonorbornadiene, oxabenzonorbornadiene, norbornene, and norbornadiene were reacted with 1,3-cyclohexanedione and ethyl acetoacetate in the presence of Mn(OAc)3 and Cu(OAc)2. Except for the reaction of benzonorbornadiene and ethyl acetoacetate, dihydrofuran derivatives were the only products obtained. The formation of naphthalene derivatives was observed together with dihydrofuran in the aforementioned benzonorbornadiene/ethyl acetoacetate reaction. Additionally, the dihydrofuran product from the addition of ethyl acetoacetate to norbornadiene was slowly converted into epoxide derivative with air. The mechanism for the formation of the products is discussed.

Three-Component Cycloaddition To Synthesize Aziridines and 1,2,3-Triazolines.

An efficient three-component cycloaddition of oxa(aza)bicyclic alkenes/norbornene in the presence of NaN3 and arylsulfonyl chlorides was developed, affording the corresponding aziridine products in good yields (up to 82%) with moderate to good endo/exo selectivities (up to >99:1 endo/exo). Further studies showed that the cycloaddition of oxa(aza)bicyclic alkenes in the presence of NaN3 and chloroalkanes could afford the exo-cycloadduct 1,2,3-triazolines in good to excellent yields (up to 95%). Compared with the existing methodologies, the current protocol demands very simple and mild reaction conditions and is a metal-free catalyzed reaction. In addition, a plausible mechanism for the cycloaddition reaction was also proposed.

Cobalt(III)-Catalyzed Intermolecular Carboamination of Propiolates and Bicyclic Alkenes via Non-Annulative Redox-Neutral Coupling.

A cobalt(III)-catalyzed, redox-neutral, intermolecular carboamination of propiolates and bicyclic alkenes was developed. This non-annulative coupling strategy features atom economy, high regioselectivity, good yields, and functional groups tolerance. Such a carboamination reaction was applied to modified phenols from the corresponding phenols under mild conditions.

Ni-Catalyzed Three-Component Alkene Carboacylation Initiated by Amide C–N Bond Activation

The nickel-catalyzed intermolecular carboacylation of alkenes with amides and tetraarylborates is presented. Bicyclic alkenes are readily functionalized with a variety of N-benzoyl-N-phenylbenzamid...

Radical Addition of Thiols to Oxa(aza)bicyclic Alkenes in Water

AbstractAn air‐promoted radical addition reaction of various thiols to oxa(aza)bicyclic alkenes is reported, leading to the corresponding exo adducts in good to excellent yields (up to 99%) in water without the use of any metal catalyst, photoredox catalyst or radical initiator reagent under mild conditions. The reaction has a wide scopeof oxa(aza)bicyclic alkenes and thiols, which provides an easy and clean way for the direct preparation of thioethers. A proposed mechanism of an exo free radical attacking the double bond of an oxa(aza)bicyclic alkene was investigated by DFT calculations of stepwise reaction pathways and control experiments.