Nonconventional allylation of norbornene and norbornadiene derivatives: stoichiometry and catalysis

The key trends for the development of catalytic reactions of allyllic esters of carboxylic acids with norbornene, norbornadiene, and their heterocyclic analogs in the presence of the nickel and palladium complexes are discussed. The main approaches to investigation of the mechanism using model stoichiometric reactions and quantum chemical calculations are described. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 823–830, April, 2008.     

Trapping of reactive intermediates in dienone photochemistry by amines

Irradiation of 4-methyl-4-trichloromethyl-2,5-cyclohexadienones in amine solvents leads to the formation of the corresponding dichloromethyl cyclohexadienones by a process involving electron transfer from the amines to zwitterion intermediates.     

Catalytic [2+2]-cycloaddition of 3,3-disubstituted cyclopropenes to norbornene and norbornadiene

Conclusions 3,3-Dialkyl(cycloalkyl)cyclopropenes react with norbornene and norbornadiene at –20°C in the presence of complexes of CuCl with (PhO)₃P or Ph₃P exclusively by [2 + 2]-cycloaddition, giving the corresponding exo,trans-tetracyclo[5.2.1.0^2,6.0^3,5]decanes (or decenes) in yields of 60–94%, the tricyclohexane cyclodimers being obtained in yields of 5–25%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1534–1540, July, 1987.     

Asymmetric induction in intramolecular meta photocycloaddition: cyclodextrin-mediated solid-phase photochemistry of various phenoxyalkenes

[reaction: see text]. An approach to the asymmetric intramolecular meta photocycloaddition of phenoxyalkenes is described. The beta-cyclodextrin complexes of several phenoxyalkenes have been synthesized and irradiated in the solid phase. The effect of the CD-hosting on the regio- and enantioselectivity is discussed. Values of ee up to 17% were obtained.     

Nonplanarity of π systems. An ab initio study of norbornene and norbornadiene

The geometry of norbornene $\text{1}$ and norbornadiene $\text{2}$ fully optimized by ab initio calculations reveals the nonplanarity of the π system(s). The exo addition of electrophiles on norbornene systems is analyzed in this context.     

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.     

Diastereoselective [2+2] photocycloaddition of polymer-supported cyclic chiral enone with ethylene

The phenylmenthyl derivative, previously shown to be very effective chiral auxiliaries in the diastereoselective [2+2] photocycloaddition of cyclic enones with the simplest olefin, ethylene, was attached to poly(ethylene glycol)-grafted Wang resin. We then investigated the diastereoselective [2+2] photocycloaddition on solid support in several solvents. As the result, we accomplished good selectivity in toluene as well as the recycle of the polymer-supported chiral auxiliary. This is the first example that bicyclo[4.2.0]octane derivative has been obtained photochemically on the solid support.     

Density functional study of the retrocyclization of norbornadiene and norbornene catalyzed by Fe(+)

In the presence of Fe(+) catalyst, the retro Diels-Alder reaction of norbornadiene (NBD) is predicted to be stepwise with an activation barrier of 18.8 kcal/mol, which is 3.1 kcal/mol lower than the concerted retro reaction. For norbornene (NBN), the Fe(+)-catalyzed retro reaction is also calculated to be stepwise with an activation barrier of 24.9 kcal/mol, which is 8.5 kcal/mol lower than the uncatalyzed stepwise reaction but 3.8 kcal/mol higher than the concerted reaction. The intermediates from the NBD and NBN retro Diels-Alder reactions, C(5)H(6)FeC(2)H(2)(+) and C(5)H(6)FeC(2)H(4)(+), are predicted to have low activation barriers for ligand-to-ligand hydrogen transfers (through an iron-hydrido intermediate) to form CpFeC(2)H(3)(+) and CpFeC(2)H(5)(+) and, ultimately, vinyl- and ethyl-substituted cyclopentadiene-iron complexes, respectively. In contrast to FeC(2)H(2)(+) and FeC(2)H(4)(+), the lowest-energy pathways on the C(5)H(6)FeC(2)H(2)(+) and C(5)H(6)FeC(2)H(4)(+) potential energy surfaces involve only one multiplicity (quartet). The C(2)H(2) and C(2)H(4) complexes of CpFe(+) and C(5)H(6)Fe(+) are compared.     

An experimental and theoretical study of the type C enone rearrangement: mechanistic and exploratory organic photochemistry

We recently described a new photochemical rearrangement which we termed a Type C process. The reaction involves a delta to alpha aryl migration in 5-disubstituted cyclohexenones also having bulky C-3 substituents. In contrast to most cyclohexenone rearrangements, the reaction occurs via a twisted pi-pi excited triplet rather than the usual n-pi state. The electronic nature of the rearrangement was assessed using migration selectivity with p-anisyl and p-cyanophenyl groups. A synthesis of the reactants was elaborated, and the product structures were established by X-ray and NMR analysis. The reaction mechanism was established further with DFT and CASSCF computations. In the latter, localized NBO basis orbitals permitted proper selection of the active space. The nature of the diradical intermediates as well as the transition states was established computationally. Sensitization experiments with regioselectivities the same as those in direct irradiation confirmed the triplet multiplicity of the process.     

The inter-and intramolecular addition of aromatic ketone triplets to quadricyclenes: Comparison with the corresponding reactivities of norbornadiene,methylenenorbornene, methylenenorbornane and norbornene

Irradiation of acetophenone or benzophenone in the presence of norbornadiene or quadricyclene gives 1: 1-adducts. These arise via reaction of the ketone triplet with the quadricyclene. Similar reactivity is exhibited in an intramolecular sense by 7-phenacylnorbornadiene and the corresponding quadricyclene. Addition of triplet benzophenone to 5-methylene norbornene is regiospecific in contrast to expectations based on a comparison of the reactivities of 2-methylenenorbornane and norbornene. The possibility is raised that, in contrast to the simple olefins and the quadricyclenes, exciplexes formed by reaction of the rigid homoconjugated dienes with the triplet ketone are endo orientated with participation of both double bounds.     

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.     

Ring opening metathesis polymerisations of norbornene and norbornadiene derivatives containing oxygen: a study on the regeneration of Grubbs catalyst

Ring opening metathesis polymerisation (ROMP) of norbornene and norbornadiene derivatives containing oxygen are investigated using Grubbs well-defined ruthenium initiator. A series of 7-alkoxy norbornadiene monomers (2b-d), containing alkoxy groups with decreasing steric hindrance in the 7-position have been prepared. The ROMP reactions of monomers showed that as the reaction proceeds the initiator is consumed first and then is partially regenerated at the expense of the propagating species. A small amount of another carbene species X, giving a broad signal at 17.44 ppm, is also formed which is extremely stable in solution. The species X is an active metathesis species and is able to perform ROMP on strained cyclic olefins. ROMP of monomers without alkoxy groups in the 7-position (3, 4a, 4b, 5a and 5b) and also monomers with alkoxy groups in the 5 and/or 6 positions of norbornene (6 and 7) have been performed under similar conditions. None of these systems exhibited regeneration of the initiator and no resonances due to species X can be seen in the ¹H NMR spectra. The results confirm that the presence of oxygen in the 7-position of the norbornadiene monomer plays an important role in the process of regeneration of the initiator. It is found that the steric bulk and the position of substituents of the monomer have a pronounced influence on the extent of regeneration of the initiator.     

Ring-opening metathesis polymerization of norbornene and norbornadiene by tungsten(II) and molybdenum(II) complexes

The reaction of norbornene (NBE) and norbornadiene (NBD) in the presence of seven-coordinate tungsten(II) and molybdenum(II) complexes of the [(CO)₄M(μ-Cl)₃M(SnCl₃)(CO)₃] and [MCl(M′Cl₃)(CO)₃(NCMe)₂] (M=W, Mo; M′=Sn, Ge) types leads to ring-opening metathesis polymerization (ROMP) and to the formation of high molecular weight polymers. The geometric structure of these polymers was determined by means of ¹H- and ¹³C-NMR spectroscopy. The monitoring of the reaction between cyclic olefins and the metal complex by means of ¹H-NMR spectroscopy allowed us to observe the coordination of NBD to metal atoms in the initiation step of the polymerization process. Compounds of the [MCl(SnCl₃)(CO)₃(η⁴-NBD)] type prepared directly from [(CO)₄M(μ-Cl)₃M(SnCl₃)(CO)₃] or [MCl(M′Cl₃)(CO)₃(NCMe)₂] (M=W, Mo) in the presence of an excess of NBD initiate the ROMP reaction immediately. The detection of the first-formed products in the reaction between the metal complex and cyclic olefins provides valuable information concerning the nature of the initiating species.     

Laser photochemistry: The intramolecular cyclization of carvone to carvonecamphor

Kr-ion laser irradiation of carvone ($\text{1}$) at 350.7 and 356.4 nm gave carvonecamphor ($\text{2}$) in a much higher yield (88%) than in conventional photochemistry, while ($\text{3}$) was a primary photo-by-product.     

Cycloaddition of norbornadiene to fluorine-containing heteroaddends

Cycloaddition reactions of norbornadiene with fluorinated heteroaddends (hexafluoro-acetone, dichlorotetrafluoroacetone, trifluoroacetonitrile, and N-trifluoroacetylhexafluoro-propan-2-imine) were studied. As a rule, the reactions follow the concerted mechanism. The reaction with bis(trifluoromethyl)ketene gave a mixture of tricyclene [2+2]- and [2+2+2]-cyclo-adducts formed along different pathways. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 1013–1015, April, 2005.