exo-Selective inverse-electron-demand hetero Diels–Alder reactions of norbornene with 5-benzylidine-2-arylimino-3-aryl-thiazolidine-4-thiones at room temperature

2-Arylimino-3-aryl-thiazolidine-4-thiones were synthesized from the corresponding thiazolidine-4-ones using Lawesson's reagent (LR) and converted into 5-benzylidine-2-arylimino-3-aryl-thiazolidine-4-thiones by reaction with benzaldehyde, which were then used as heterodienes in the inverse-electron-demand hetero Diels–Alder cycloadditions with norbornene as a dienophile at 25 ^°C. The reactions with norbornene were found to proceed with 100% exo-selectivity as determined by NMR experiments. The hetero Diels–Alder reactions with axially chiral heterodienes with ΔG^#>116 kJ/mol showed kinetic atroposelectivities up to 11:1. However, the products were found to equilibrate, as revealed by the 97.1 kJ/mol barrier to hindered rotation of the most sterically hindered product, to produce 2:1 diastereoselectivities after the 24 h reaction time.     

Stannylation of unsaturated carbon-carbon bonds by tin tetrachloride

The reactions of tin tetrachloride and four terminal alkynes (PhCCH, ^tBuCCH, ⁿBuCCH, HOCH₂CCH), norbornene, and norbornadiene in dichloromethane or chloroform solution lead to the formation of stannylation products, which were characterized by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. Virtually complete α-regioselectivity was obtained in reaction of all four alkynes without any effect of the relative steric bulk of the substituent R at the triple bond of alkyne RC_βC_αH. The reaction of norbornene and norbornadiene with SnCl₄ is stereoselective, giving an exo stannylation product.     

Stereo- and regioselective cycloaddition of norbornene to 2,4,9-triazidopyridine

4-(3-Azatricyclo[3.2.1.0]oct-3-yl)-2,6-diazido-3,5-dicyanopyridine has been obtained by the reaction of 2,4,6-triazido-3,5-dicyanopyridine with an equimolar quantity of norbornene. The product reacted readily at room temperature with an excess of norbornene giving the corresponding trisazatricyclooctane cycloadduct. An analogous trisadduct was obtained in the reaction of 4-(3-azatricyclo[3.2.1.0]oct-3-yl)-1,6-diazido-3-chloro-5-cyanopyridine with norbornene on boiling in CCl₄, and also in ether at room temperature in the presence of the complexes Rh₂(OAc)₄ and Cu(AcAc)₂. The cycloaddition proceeds stereoselectively in all cases with the exclusive formation of exo-conformers. Calculations have been carried out using the PM3 and RHF/3-21G^* methods on 2,4,6-triazido-3-chloro-5-cyanopyridine and on 2,4,6-triazido-3,5-dicyanopyridine and also on the cycloadducts of these compounds with one or two molecules of norbornene. It was established that the addition of norbornene at the azide groups of pyridine is a dipole-LUMO controlled type of reaction and leads to the formation of cycloadducts having higher LUMO energy than the initial azides. The energy of the LUMO is increased to a lesser extent as a result of the addition of norbornene to a triazide containing identical substituents in the β positions of the pyridine ring, and is due to the special features of the symmetry of the LUMO of the cycloadducts formed. Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, Chernogolovka 142432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1521–1532, November, 1997.     

Metathesis copolymerization of 1,5-cyclooctadiene and norbornene with electrochemically generated WCl6-based active species

The copolymerization of 1,5-cyclooctadiene and norbornene in the presence of an electrochemically generated WCl₆-based catalyst was investigated. This copolymer was isolated and characterized by ¹H, and ¹³C NMR spectroscopy to analyse in detail the nature of homo- and heterodyad units and GPC analysis (Mn = 11200, PDI = 2.0). Homopolymerizations of 1,5-cyclooctadiene and norbornene were also studied and resulting polymers were characterized by spectroscopic methods to discuss with copolymers. Glass-transition temperatures of homo- and copolymers were determined by DSC.     

An unusual way of the reaction of PI3 with norbornene and norbornadiene

The iodination of norbornene and norbornadiene with phosphorus triiodide in the presence and in the absence of weak electrophiles (arylsulfenamides orN-chloramines) and with elemental iodine was studied. Depending on the reaction conditions, the reactions resulted in mono- or diiodides of the norbornene and norbornadiene series. All the compounds obtained were characterized by¹H and¹³C NMR spectra.     

Living copolymerization of ethylene with norbornene mediated by heteroligated (Salicylaldiminato)(β‐enaminoketonato)titanium catalysts

Three heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐Bu^t‐2‐OC₆H₃CH?N(C₆F₅)][(p‐XC₆H₄)N?C(Bu^t)CHC(CF₃)O]TiCl₂ ( 3a : X = F, 3b : X = Cl, 3c : X = Br) were synthesized and investigated as the catalysts for ethylene polymerization and ethylene/norbornene copolymerization. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts exhibited high activities toward ethylene polymerization, similar to their parallel parent catalysts. Furthermore, they also displayed favorable ability to efficiently incorporate norbornene into the polymer chains and produce high molecular weight copolymers under the mild conditions, though the copolymerization of ethylene with norbornene leads to relatively lower activities. The sterically open structure of the β‐enaminoketonato ligand is responsible for the high norbornene incorporation. The norbornene concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resulting copolymer. When the norbornene concentration in the feed is higher than 0.4 mol/L, the heteroligated catalysts mediated the living copolymerization of ethylene with norbornene to form narrow molecular weight distribution copolymers (M_w/M_n < 1.20), which suggested that chain termination or transfer reaction could be efficiently suppressed via the addition of norbornene into the reaction medium. Polymer yields, catalytic activity, molecular weight, and norbornene incorporation can be controlled within a wide range by the variation of the reaction parameters such as comonomer content in the feed, reaction time, and temperature. ©2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6072–6082, 2009     

Investigation of the microstructure of metallocene-catalyzed norbornene–ethylene copolymers using NMR spectroscopy

Norbornene–ethylene copolymers were prepared using the metallocene catalyst ethylene bis (indenyl) zirconium dichloride with MAO, and their microstructure was characterized with ¹H-NMR and ¹³C-NMR methods. From a Cosy ¹H-NMR spectrum it was found that all norbornene units are enchained in the exo-configuration. The sequence distribution of norbornene units was investigated using ¹³C-¹H correlations, hmqc for one-bond correlations, and hmbc for two- or three-bond correlations. It was shown that norbornene diads were formed at a high norbornene content (45 mol %). When further increasing the norbornene incorporation (66 mol %) a number of new signals were obtained. A Cosy ¹H-NMR spectrum revealed a new crosspeak which, according to the corresponding ¹³C-NMR shifts (hmqc), correlated well with a terminal unit of a trimer of norbornene. This means that at very high norbornene contents, norbornene triads can be formed. Because the formation of isotactic norbornene triads is very difficult to understand from a sterical point of view, an epimerization process causing stereoirregularities in the norbornene triad is proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1633–1638, 1998     

Synthesis of Some Novel Norbornene‐Fused Pyridazines as Potent Inhibitors of Carbonic Anhydrase and Acetylcholinesterase

The reaction of benzocyclic norbornene derivatives with tetrazines provided the 1,3‐dihydropyridazine derivatives as a single product. The dihydropyridazine derivatives have been dehydrogenated with phenyliodine bis(trifluoroacetate) to yield the corresponding pyridazines in a high yield. Two stable diazines, primary product of corresponding 1,4‐dihydropyridazine, were also isolated. Structures were then determined by ¹H‐NMR, and ¹³C‐NMR beside to elemental analyses. The novel pyridazine derivatives ( 8 , 9 ) efficiently inhibited the cytosolic human carbonic anhydrase isoenzymes I and II (hCA I and II). In addition, these novel pyridazine derivatives ( 8 , 9 ) were evaluated for their in vitro acetylcholinesterase inhibitory activity. Ligand–receptor interactions are tested using molecular docking simulations. Obtained docking scores are in good agreement with in vitro results.     

Homo- and copolymerizaton of norbornene and norbornene derivative with Ni- and Pd-based β-ketoiminato complexes and MAO

Neutral nickel(II) and palladium(II) complexes bearing β-ketoiminato ligand have been synthesized. The two complexes have been investigated as catalyst for the polymerization. Using methylaluminoxane (MAO) as a cocatalyst, both complexes produce vinyl-addition polynorbornenes, but palladium(II) complex displays much higher activity up to 8.0 × 10⁷ g/(molPd h). Furthermore, both Ni(II) and Pd(II)/MAO system can efficiently copolymerize norbornene and 5-norbornene-2-yl acetate (NB-OCOMe) in moderate yields and in relatively high molecular weights. The analyses of the product by FTIR, ¹H NMR and ¹³C NMR spectra give the verification of vinyl addition copolymer. The copolymers show narrow molecular weight distribution and good solubility in common organic solvents.     

Effect of substituents on addition polymerization of norbornene derivatives with two Me3Si-groups using Ni(II)/MAO catalyst

Addition polymerization and copolymerization of bis(Me₃Si)-substituted norbornene-type monomers such as 5,5-bis(trimethylsilyl)norbornene-2, 2,3-bis(trimethylsilyl)norbornadiene-2,5 and 3,4-bis(trimethylsilyl)tricyclo[4.2.1.0^2,5]nonene-7, in the presence of Ni(II) naphtenate/MAO catalyst were studied. Disubstituted norbornene and norbornadiene were found to be practically inactive in homopolymerization. On the other hand, their copolymerization with norbornene proceeded with moderate yields of copolymers containing predominantly norbornene units. Under studied reaction conditions 2,3-bis(trimethylsilyl)norbornadiene-2,5 was transformed into the only exo-trans-exo-dimer as a result of the [2+2]-cyclodimerization reaction. Moving Me₃Si-substituents one carbon atom away from norbornene double bond made 3,4-bis(trimethylsilyl)tricyclo[4.2.1.0^2,5]nonene-7 active in homopolymerization and allowed to obtain addition homo-polymer with two Me₃Si-substituents in each elementary unit. The reaction mechanism and steric effect of Me₃Si-substituents are also discussed.     

Vinylcyclopropanation of norbornadiene,norbornene, and dispiroheptadiene by methyl esters of 1-alkylcyclopropene-3-carboxylic acids

Methyl esters of 1-alkylcyclopropene-3-carboxylic acids (I) in the presence of CuCl·P(OPh)₃ cyclopropanate the intracyclic norbornene double bonds of norbornene, norbornadiene, and dispiroheptadiene to give the corresponding vinylcyclopropane adducts in yields up to 80%. 3,5-Dioxo-4-oxatricyclo[5.2.1. 0^2,6]dec-8-ene and 5-acetyl-7-oxabicyclo[2.2.1]hept-2-ene, which are heteroanalogs of dicyclopentadiene and norbornene, are inert relative to (I).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 214–216, January, 1990.     

Palladium(II)‐Initiated Catellani‐Type Reactions

The Catellani reaction is known as a powerful strategy for the expeditious synthesis of highly substituted arenes and benzo‐fused rings, which are usually difficult to access through traditional cross‐coupling strategies. It utilizes the synergistic interplay of palladium and norbornene catalysis to facilitate sequential ortho C?H functionalization and ipso termination of aryl halides in a single operation. In classical Catellani‐type reactions, aryl halides are mainly used as the substrates, and a Pd⁰ catalyst is required to initiate the reaction. Nevertheless, recent advances showcase that Catellani‐type reactions can also be initiated by a Pd^II catalyst with different starting materials instead of aryl halides via different reaction mechanisms and under different conditions. This emerging concept of Pd^II/norbornene cooperative catalysis has significantly advanced Catellani‐type reactions, thus enabling future developments of this field. In this Minireview, Pd^II‐initiated Catellani‐type reactions and their application in the synthesis of bioactive molecules are summarized.     

High norbornene incorporation in ethylene-norbornene copolymerization with a bis(α-alkyloxoimine) titanium-MAO catalyst

A novel bis(α-alkyloxoimine) titanium(IV) complex was synthesized and used as a catalyst precursor to catalyze homo- and copolymerization of ethylene and norbornene. The titanium complex activated with methylalumoxane exhibits good activities for the homopolymerizations of ethylene and norbornene under high temperature to produce high-molecular-weight linear polyethylene and vinyl-type polynorbornene, respectively. Ethylene-norbornene copolymers with high molecular weight can also be produced by this catalyst. The incorporation of norbornene from 0 to 76 mol% in the copolymers can be controlled by varying the charged norbornene. ¹³C NMR analyses show that the microstructures of the ethylene-norbornene copolymers with low norbornene incorporation are predominantly alternated and isolated norbornene units, while those with high norbornene incorporation are random polymers containing long norbornene sequences.     

Photochemical reaction of W(CO)6 with GeCl4 as a source of germyl and germylene compounds acting as initiators for ring-opening metathesis polymerization of norbornene

Photolysis of W(CO)₆ in a solution of n-heptane containing GeCl₄ leads to the formation of two seven-coordinate compounds with direct WGe bonds: [(CO)₄W(μ-Cl)₃W(GeCl₃)(CO)₃] (1) and [(μ-GeCl₂){W(CO)₅}₂] (2). The molecular structures of these two tungsten-germanium compounds have been established by single-crystal X-ray diffraction studies. The germyl compound 1 is a previously synthesized binuclear complex of tungsten(II) with a d⁴ electronic configuration, while in the new germylene compound 2 the tungsten atom is formally in the zero oxidation state with a d⁶ electronic configuration and a direct WW bond. In an attempt to establish whether compounds 1 and 2 could be used as precatalysts for the ring-opening metathesis polymerization (ROMP) of cyclic olefins, their reactivity towards norbornene has been studied. In chloroform-d₁ solution the ROMP reaction is accompanied by the formation of a new olefin, 2,2′-binorbornylidene (bi-(NBE)), as a result of carbene-carbene coupling. In reaction of norbornene carried out in benzene solution the ROMP reaction is accompanied by the formation of 2-phenylnorbornane (hydroarylation product) and small amounts of bi-(NBE). In general, in the presence of olefin, compound 2 undergoes rearrangement to give an olefin compound of the type [(WCO)₅(η²-olefin)].     

Highly active ethylene polymerization and copolymerization with norbornene using bis(imino‐indolide) titanium dichloride–MAO system

A catalytic system of new titanium complexes with methylaluminoxane (MAO) was found to effectively polymerize ethylene for high molecular weight polyethylene as well as highly active copolymerization of ethylene and norbornene. The bis (imino‐indolide)titanium dichlorides (L₂TiCl₂, 1 – 5 ), were prepared by the reaction of N‐((3‐chloro‐1H‐indol‐2‐yl)methylene)benzenamines with TiCl₄, and characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. The solid‐state structures of 1 and 4 were determined by X‐ray diffraction analysis to reveal the six‐coordinated distorted octahedral geometry around the titanium atom with a pair of chlorides and ligands in cis‐forms. Upon activation by MAO, the complexes showed high activity for homopolymerization of ethylene and copolymerization of ethylene and norbornene. A positive “comonomer effect” was observed for copolymerization of ethylene and norbornene. Both experimental observations and paired interaction orbital (PIO) calculations indicated that the titanium complexes with electron‐withdrawing groups in ligands performed higher catalytic activities than those possessing electron‐donating groups. Relying on different complexes and reaction conditions, the resultant polyethylenes had the molecular weights M_w in the range of 200–2800 kg/mol. The influences on both catalytic activity and polyethylene molecular weights have been carefully checked with the nature of complexes and reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3415–3430, 2007     

An effective route for the synthesis of cationic palladium complexes of general formula [(Acac)PdLL]A

A series of palladium complexes of general formula [(Acac)PdL¹L²]⁺A⁻, where L¹, L² = phosphines and A = BF₄, CF₃SO₃, were synthesized. Preliminary studies show that the complexes are active in selective dimerization of styrene and addition polymerization of norbornene.     

Unusual selective allylation of norbornadiene in the presence of palladium nanoclusters

The reaction of norbornadiene (NBD) with allyl acetate in the presence of the nanocluster Pd₁₄₇phen₃₂O₆₀(OCOBu^t)₃₀ (Pd-147; phen is 1,10-phenanthroline) and PPh₃ in acetonitrile is nonselective and is accompanied by the decomposition of the cluster, affording the same allylation products of NBD as the reaction with Pd₃(OAc)₆ or Pd(dba)₂ (dba is dibenzylideneacetone) combined with PPh₃. In contrast, in the ionic liquid [bmim][BF₄] (bmim is 1-butyl-3-methylimidazolinium), the Pd-147 is not decomposed and the reaction occurs selectively to give methylidene(vinyl)norbornene as the sole product. The data obtained suggest that in an ionic liquid, the reaction under study is catalyzed by the nanocluster Pd-147 rather than by the products of its decomposition.     

A new versatile binuclear seven-coordinate complex of molybdenum(II), [(μ-Cl)2{Mo(μ-Cl)(SnCl3)(CO)3}2]

The two new seven-coordinate anionic complexes of molybdenum(II), binuclear [(μ-Cl)₂{Mo(μ-Cl)(SnCl₃)(CO)₃}₂]²⁻ and mononuclear [MoCl₃(GeCl₃)(CO)₃]²⁻, have been synthesized and characterized by single-crystal X-ray diffraction studies. The binuclear complex exhibits a unique mode of reactivity towards norbornene. In a strictly anhydrous atmosphere the binuclear complex effectively initiates the ring-opening metathesis polymerization reaction of norbornene, but in the presence of water norbornene is efficiently transformed to the binorbornyl ether (C₇H₁₁)₂O.     

Cobalt-catalyzed cyclotrimerization of diynes with norbornenes in one efficient step

An efficient cobalt-catalyzed [2+2+2] cyclotrimerization of diynes and norbornene is described. Treatment of diyne with norbornene in the presence of CoI₂(PPh₃)₂ and zinc powder in 1,2-dichloroethane at 80 °C for 12 h afforded [2+2+2] cyclotrimerization adduct exclusively in good yields. These cobalt-catalyzed results are in contrast to the ruthenium-catalyzed reaction of diyne with norbornene reported previously.     

Studies on the copolymerization of norbornene with CO catalyzed by a new catalytic system PdCl<Subscript>2</Subscript>/phen/M(CF<Subscript>3</Subscript>SO<Subscript>3</Subscript>)<Subscript>n</Subscript>

A new three-component catalytic system, PdCl₂/phen/M(CF₃SO₃)_n where M = La, Y, Yb, Zn, and Cu, was studied for the copolymerization of norbornene (NBE) with CO to prepare polyketone (PK). It was found that the CF₃SO₃H catalytic system gave a low catalytic activity for the copolymerization of norbornene with CO, but when M(CF₃SO₃)_n was introduced instead of CF₃SO₃H, the PdCl₂/phen/M(CF₃SO₃)_n catalytic system exhibited much higher activity. The effects of ligands, M(CF₃SO₃)_n, solvents, and temperatures on the copolymerization have been discussed in detail. The results showed that with 1,10-phenanthroline (phen) and Cu(CF₃SO₃)₂ used as cocatalysts, the corresponding reaction rate reached 82 000 g PK (mol Pd)⁻¹h⁻¹ when the reaction was carried out in methanol at 90°C and 3.0 MPa of CO, and the weight average molecular weight (M _w) of the resultant copolymer is 1090 g/mol. The copolymer was characterized with various techniques such as FT-IR, ¹HNMR, ¹³CNMR, TGA, and DSC. The infrared spectrum of the product includes two features at 1697 and 1732 cm⁻¹ for the NBE/CO copolymer in CH₃OH that are attributed to carbonyl groups in ketones (repeating unit) and esters (end group), respectively. Due to the tension of the ring of norbornene, the degree of copolymerization is not high. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 1, pp. 51–58. This article was submitted by the authors in English.