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.     

Molecular enthalpies: 2. ground-state thermodynamic and computed enthalpies of bicyclo[2.2.2]octa-2,5,7-triene and its hydrogenation products

This article is a continuation of our investigation of enthalpies of formation and strain-compensated enthalpies of hydrogenation of medium-sized hydrocarbons. We have carried out calculations of H _f by MM2, MM3, and by the MNDO, AM1, and PM3 semi-empirical molecular orbital methods. Results are given for the bicyclo[2.2]octa-2,5,7-triene series ([2.2.2]barrelenes) Two of these compounds are potentially homoantiaromatic. Comparisons with ab initio calculations are made. A novel method of estimating strain relaxation during the stepwise hydrogenation of [2.2.2]barrelene is given.     

Stereostructure of 8-chloro-5,6-di(methoxycarbonyl)-4,7-dimethyl-2-ethoxy-2-phosphabicyclo[2.2.2]octa-5,7-diene 2-oxide

The first X-ray structure of a phosphabicyclooctadiene, together with the NMR and mass spectral characterization of its isomers, is reported. © John Wiley & Sons, Inc.     

Dibenzo[b, e]-7,7,8,8-tetraneopentyl- and dibenzo[b, e]-7,7,8,8-tetraisopropyl-7,8-disilabicyclo[2.2.2]octa-2,5-dienes: interaction with tetracyanoethylene and transition metal chlorides

Dibenzo[b,e]-7,7,8,8-tetraalkyl-7,8-disilabicyclo[2.2.2]octa-2,5-dienes (1: R = ^tBuCH₂; 2: R = ⁱPr) were prepared by the reaction of ClR₂SiSiR₂Cl with lithium anthracenide in 1,2-dimethoxyethane (DME) at room temperature. The structure of 1 was determined by X-ray crystallography. Crystal data for 1: monoclinic, rC2/c, A = 12.941(2), B = 14.601(1), C = 35.109(6) Å, β = 94.957(7)°, V = 6609(2) ų, Z= 8, R = 0.048, R_w = 0.053 for 4037 reflections. Compounds 1 and 2 show the bathochromic shift of ¹L_a and ¹L_b bands in UV spectra and exhibit considerably low oxidation potentials due to effective σ-π conjugation. Compounds 1 and 2 form charge-transfer complexes with tetracyanoethylene (TCNE). In the case of 1, the charge-transfer complex (1: TCNE = 2: 1) could be isolated as crystals and the structure was determined by X-ray crystallography. Crystal data for the 1-TCNE complex: monoclinic, C2/c, A= 10.267(2), b = 36.077(4), C = 20.022(4) Å, β = 100.680(8)°, V = 7288(2) ų, Z = 4, R = 0.045, R_w = 0.077 for 4120 reflections. The action of transition metal chlorides on 2 resulted in [4+2] cycloreversion to form ClⁱPr₂SiSiⁱPr₂Cl and anthracene.     

The reaction of mercuric salts with dimethyl bicyclo[2.2.2]octa-2,5-diene-5,6-dicarboxylate

The regioselectivity and stereochemistry of the reaction of mercuric salts with dimethyl bicyclo[2.2.2.]octa-2,5-diene-5,6-dicarboxylate were studied in different solvents. The factors determining the reaction regioselectivity were considered.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1642–1645, September, 1993.     

Synthetic study of optically active and C2-symmetric novel ligand, 7,8-bis(benzyloxy)bicyclo[2.2.2]octa-2,5-diene and a tricarbonyliron complex

The 7,8-bis(benzyloxy)bicyclo[2.2.2]octa-2,5-diene derivatives have been synthesized via Diels-Alder reaction of optically active 5,6-bis(benzyloxy)cyclohexa-1,3-diene and dienophiles. The corresponding tricarbonyliron complexes have also been synthesized in enantiomerically pure form.     

Preparation of C2-symmetric bicyclo[2.2.2]octa-2,5-diene ligands and their use for rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids

[reaction: see text] C2-symmetric bicyclo[2.2.2]octa-2,5-dienes containing benzyl, phenyl, and substituted phenyl groups at 2 and 5 positions were prepared enantiomerically pure by way of bicyclo[2.2.2]octane-2,5-dione as a key intermediate. These chiral diene ligands were successfully applied to rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to alpha,beta-unsaturated ketones. High enantioselectivity (up to 99% ee) as well as high catalytic activity was observed in the addition to both cyclic and linear substrates.     

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.     

Bicyclic allenes : Generation and trapping of 6,7-benzobicyclo [3.2.1] octa-2,3-diene

Treatment of 3-bromo-6,7-benzobicyclo [3.2.1] octa-2,3-diene (9) with potassium tert.-butoxide produces the strained bicyclic allene (10) which is trapped by 1,3-diphenylbenzo[c]furan (DBI) to give five isomeric cycloadducts. In the absence of DBI, allene (10) gave rise to enol ether (18) by addition of tert.-butanol.     

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).     

Siliciumverbindungen mit starken intramolekularen sterischen wechselwirkungen: XXIV. Cyclohexylsubstituierte disilane: darstellung und reaktionen von disilenyl-radikalanionen, 2,3:5,6-dibenzo-7,8-disilabicyclo[2.2.2]octa-2,5-dienen und eines cyclotetrasilans

Treatment of 1,2-di-t-butyl-1,2-dicyclohexyl-1,2-dichlorodisilane (5b) with excess lithium yields the long-lived radical anion t-Bu(Cy)SiSi(Cy)t-Bu

, which has been characterized by its ESR spectra. Reaction of 5 as well as 1,1,2,2-tetracyclohexyl-1,2-dihalodisilanes (6) with lithium in the presence of anthracene gives 7,8-tetraorganyl-2,3 : 5,6-dibenzo-7,8-disilabicyclo[2.2.2]octa-2,5-dienes which can be cleaved photochemically forming the corresponding cyclotetrasilanes. In the presence of phenylacetylene 5 and 6 react with lithium to give the 1,2-bis(phenylethinyl)-substituted disilanes and 3,4,5,6-tetra-t-butyl-3,4,5,6-tetracyclohexyl-2-phenyl-3,4,5,6-tetrasilacyclohexen-1, respectively. The latter compound is also obtained by phenyl-acetylene insertion into 1,2,3,4-tetra-t-butyl-1,2,3,4-tetracyclohexylcyclotetrasilane.