Enzymatic desymmetrization of prochiral 2,3-bis(acetoxymethyl)bicyclo[2.2.1]hepta-2,5-diene and 2,3-bis(hydroxymethyl)bicyclo[2.2.1]hepta-2,5-diene

Enzymatic desymmetrization of the title compound 1 is reported using various commercially available lipases in hydrolysis and alcoholysis reactions or ester synthesis. In this area, lipase Amano AK (Pseudomonas sp.) proved to be the best lipase whatever the experimental conditions used. The monoacetate product 2 is indifferently obtained with more than 95% enantiomeric excess (ee) as the levorotatory enantiomer 2a or the dextrorotatory one 2b.     

Transition metal-catalyzed [4 + 2 + 2] cycloadditions of bicyclo[2.2.1]hepta-2,5-dienes (norbornadienes) and bicyclo[2.2.2]octa-2,5-dienes

The transition-metal-catalyzed [4 + 2 + 2] cycloadditions of norbornadienes, bicyclo[2.2.2]octa-2,5-diene, and benzobarrelene with 1,3-butadienes proceed in excellent yields using cobalt-based catalytic systems. Two key distinctions between these [4 + 2 + 2] cycloadditions and the corresponding transition-metal-catalyzed [2 + 2 +2] reactions of norbornadiene are the requirement of a bimetal catalytic system with a bisphosphine ligand for the former and exclusive regioselectivity in the [4 + 2 + 2] reaction of 2-substituted norbornadienes to produce 1-substituted adducts. These distinctions may indicate two distinct mechanisms for the [4 + 2 + 2] and [2 + 2 + 2] reactions.     

Preparation of bicyclo[2.2.1]hepta-2,5-diene by the condensation of cyclopentadiene with acetylene

Summary The condensation of cyclopentadiene with acetylene under pressure gave a 40–45% yield of bicyclo[2.2.1]hepta-2.5-diene, the starting material for the synthesis of the insecticide aldrin.     

Ruthenium-catalyzed [2+2] cycloadditions of alkynyl sulfides and alkynyl sulfones

Ruthenium-catalyzed [2+2] cycloadditions of bicyclic alkenes with alkynyl sulfides and alkynyl sulfones were investigated. The sulfide and sulfone moieties were found to be compatible with the Ru-catalyzed cycloadditions, giving the corresponding cyclobutene cycloadducts in good yields. The sulfonyl-containing cycloadducts can be transformed into a variety of products that are difficult to obtain via direct cycloaddition.     

Cyclodimerization of bicyclo[2.2.1]hepta-2,5-diene in the presence of rhodium-containing zeolite catalysts

It has been shown that norbornadiene is dimerized in the presence of rhodium-containing zeolite catalysts, forming hexacyclic [4+2]dimers preferentially. The effect of the structure and the method of preparation and pretreatment of the catalysts on their activity and selectivity in norbornadiene cycloaddition was studied. The influence of the above parameters on the change in the electronic state of rhodium in the course of the reaction was also investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1913–1919, November, 1994.     

Dimerization of bicyclo[2.2.1]hepta-2,5-diene in the presence of rhodium carboxylate complexes

Conclusions Bicyclo [2.2.1]hepta-2,5-diene (norborndiene) dimerizes in the presence of Rh (II) carboxylate complexes Rh₂(RCOO)₄ (R=CH₃, CF₃) at 25–100°C to form preferentially the products of (4+2) cycloaddition. The rate of the reaction in the presence of Rh₂ (CF₃COO)₄ is an order of magnitude higher than for Rh₂(CH₃COO)₄. Under the reaction conditions Rh(II) is reduced by norbornadiene to Rh(I).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 635–639, March, 1982.     

Photochemical isomerization of 1,2,5-trisilabicyclo[3.2.0]hepta-3,6-diene to 1,4,7-trisilabicyclo[2.2.1]hepta-2,5-diene

Upon irradiation of a benzene-d6 solution of 1,2,2,5-tetrakis[di-tert-butyl(methyl)silyl]-4,7-diaryl- 1,2,5-trisilabicyclo-[3.2.0]hepta-3,6-diene [1a: aryl = phenyl, b: aryl = 3,5-bis-(trimethylsilyl)phenyl], 1,4,7,7-tetrakis[di-tert-butyl-(methyl)silyl]-2,5-diaryl-1,4,7- trisilabicyclo[2.2.1]hepta-2,5-diene (2a,b) was formed via skeletal rearrangement.     

Opening the [4 + 2 + 2] cycloadducts of bicyclo[2.2.1]hepta-2,5-dienes (norbornadienes) to cis-fused bicyclo[5.3.0]decanes

Tetracyclo[5.4.0.0.(2,4)0(3,7)]undec-9-enes, prepared by the transition-metal-catalyzed [4 + 2 + 2] homo-Diels-Alder reactions of norbornadiene and 1,3-butadienes, can be opened using either acid-promoted or Zeise's dimer-mediated cyclopropane ring cleavage, ultimately leading to cis-fused bicyclo[5.3.0]decanes (perhydroazulenes). Stereoselective functionalization of the olefin unit in the tetracycloundecenes to an alcohol or diol prior to ring opening is tolerated by the Zeise's dimer ([Pt(C(2)H(4))Cl(2)](2)) catalyst to yield highly functionalized bicyclo[5.3.0]decanes, which form the core structure of numerous sesquiterpenes.     

Ruthenium-catalyzed [2 + 2] cycloadditions between bicyclic alkenes and alkynyl halides

Ru-catalyzed [2 + 2] cycloadditions between norbornadiene and alkynyl halides were found to occur in moderate to good yields (32-89%). The presence of the halide moiety greatly enhances the reactivity of the alkyne component in the cycloaddition and can be transformed into a variety of products that are difficult or impossible to obtain via direct cycloaddition. [reaction: see text]     

The Radical Cations of Bicyclo[2.2.1]hepta-2,5-diene (8,9,10-Trinorborna-2,5-diene) and bicyclo[2.2.2]octa-2,5-diene (2,3-Dihydrobarrelene). An ESR and ENDOR study

The radical cation of bicyclo[2-2.1]hepta-2,5-diene (8,9,10-trinorborna-2,5-diene; 1 ) in CF₂ClCFCl₂, and CF₃CCl₃ matrices and that of bicyclo[2.2.2]octa-2,5-diene (2,3-dihydrobarrelene; 2 ) in CFCl₃ and CF₃CCl₃ matrices have been studied by ESR and ENDOR spectroscopy. For ${\bf 1}^{+ \atop \dot{}}$, the coupling constants of the olefinic, methano-bridge, and bridgehead protons are ?0.780 ±0.005, +0.304±0.002, and ?0.049±0.002 mT, respectively. The hyperfine tensor for the methano-bridge protons is axial, A_x = +0.263 ± 0.002 and A_y = +0.386 ± 0.002 mT, while that for the olefinic protons is orthorhombic, A_x = ?0.594 ± 0.005, A_y= ?0.913 ± 0.005, and A_z = ?0.834 ± 0.005 mT (x parallel to C? H- z parallel to 2p_π axis). For ${\bf 2}^{+ \atop \dot{}}$, the coupling constants of the olefinic, ethano-bridge, and bridgehead protons are ?0.68 ± 0.01, +0.162 ± 0.005, and ?0.108 ± 0.005 mT, respectively. The hyperfine data for ${\bf 1}^{+ \atop \dot{}}$ and ${\bf 2}^{+ \atop \dot{}}$ fully support the presentation of their singly occupied orbitals as antisymmetric combinations, b₂(π), of the two bonding ethene π-MO's.     

Ruthenium-catalyzed [2 + 2] cycloadditions of ynamides

Ruthenium-catalyzed [2 + 2] cycloadditions between norbornene and ynamides were investigated. The ynamide moiety was found to be compatible with the ruthenium-catalyzed cycloaddition conditions, giving the corresponding cyclobutene cycloadducts in moderate to good yields (up to 97%). [reaction: see text]     

Expanding the C2-symmetric bicyclo[2.2.1]hepta-2,5-diene ligand family: concise synthesis and catalytic activity in rhodium-catalyzed asymmetric addition

New C2-symmetric bicyclo[2.2.1]hepta-2,5-dienes bearing methyl and phenyl substituents at the 2 and 5 positions were prepared enantiomerically pure through a two-step sequence starting from the readily available bicyclo[2.2.1]hepta-2,5-dione. Due to the instability or volatility of these dienes, their isolation was achieved through the formation of the corresponding stable [RhCl(diene)]2 complexes. These chiral rhodium complexes displayed high activity and enantioselectivity (up to 99% ee) in the rhodium-catalyzed 1,4-addition and 1,2-addition of phenylboronic acid to cyclic enones and N-sulfonylimines, respectively.     

2,3-Dichlorobicyclo[2.2.1]hepta-2,5-diene: A Convenient Precursor of Norbornadiene-2,3-diynes

Norbornadienes that feature the properties of norbornadiene and of the ene-diyne in the same molecule have been prepared via a simple and high-yielding route starting fromdichlorobicyclo[2.2.1]hepta-2,5-diene (1).     

A homo Diels-Alder approach to bicyclo[4.2.1]nonanes

[reaction: see text] A new, high-yielding route to functionalized bicyclo[4.2.1]nonanes has been achieved utilizing homo Diels-Alder chemistry with subsequent Zeise's dimer-catalyzed opening of the cycloadduct.     

Reaction of bicyclo[2.2.1]hepta-2,5-diene with the arenesulfenamide—phosphorus(v) oxohalide system: chemo-, regio-, and steroselectivity

The chemo-, regio- and stereoselectivities of electrophilic sulfenylation of bicyclo[2.2.1]hepta-2,5-diene with arenesulfenamides activated by phosphorus(v) oxohalides were studied. The ratio of the products of endo- to exo-attack of the diene by the electrophilic species depends on the solvent nature. The proportions of the products formed upon addition to one double bond and upon homoallylic participation of the second double bond depend on solvent polarity, the nature of the halogen, the substituents in the sulfenamide benzene ring, and on the reaction time. In addition, the formation of mixed adducts was proven for the reaction carried out in acetonitrile and the formation of disulfenylation products was found in the reaction with excess sulfenylating reagent. Isomerization of exo-3-arylthio-endo-2-halobicyclo[2.2.1]hept-5-enes to the products formed with homoallylic participation of the second double bond, exo-5-arylthio-endo-3-halotricyclo[2.2.1.0^2,6]heptanes, was shown to be possible.