The Preparation of Optically Pure 7-Oxabicyclo [2.2.1]hept-2-ene Derivatives. The CD Spectrum of (+)-(1R)-7-Oxabicyclo [2.2.1]hept-5-en-2-one

(?)-1-Camphanoyloxyacrylonitrile (=(?)-1-cyanovinyl camphanate; 1 ) obtained from the commercially available (?)-camphanoyl chloride and 2-oxo-propiononitrile added to furan at 20° in the presence of Cu (BF₄)₂ · 6H₂O or ZnI₂ and gave a mixture of 2-cyano-7-oxabicyclo [2.2.1]hept-5-en-2-yl camphanates ( 2–5 ) from which isomer 5 could be obtained pure by crystallization. The latter was transformed into (+)-(1R)-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 6 ) in high yield and optical purity. Adducts 2–4 were recycled into 1 +furan by heating in toluene, and (?)-camphanic acid was recovered after saponification of 5 . The absolute configuration of 6 was deduced from its CD spectrum which showed two 1200-cm_?1 Franck-Condon series for its n→π transition.     

Synthesis and Epoxidation of 5-(2-Aminoethyl)bicyclo[2.2.1]hept-2-ene Derivatives

A number of derivatives of 5-(2-aminoethyl)bicyclo[2.2.1]hept-2-ene (85-90% of the endo isomer) were synthesized by reactions with p-nitrobenzenesulfonyl chloride, p-toluenesulfonyl chloride, benzoyl chloride, p-nitrobenzoyl chloride, benzyl isocyanate, m-tolyl isocyanate, phenyl isothiocyanate, and endic anhydride. By reactions of the resulting sulfon- and carboxamides with peroxyphthalic acid generated in situ from phthalic anhydride and 40-45% hydrogen peroxide the corresponding epoxy derivatives were obtained. These reactions were not accompanied by heterocyclization into azabrendane derivatives, which is typical of homologous N-(p-nitrophenylsulfonyl)-endo-5-aminomethylbicyclo[2.2.1]hept-2-ene.     

Photoreaction of 5-dicyanomethylenebicyclo[2.2.1]hept-2-ene

Irradiation of 5-dicyanomethylenebicyclo[2.2.1lhept-2-ene induces new types of photoreactions, i.e., unprecedented skeletal rearrangement leading to 7,7-dicyano-6-methylenebicyclo[3.1.1]hept-2-ene, and novel 1,3-carbon shifts to bicyclo[3.2.0]- and bicyclo[4.1.0]heptene.     

Synthesis of 2-(Bicyclo[2.2.1]hept-2-yloxy)ethyl Carboxylates

Esterification of aliphatic carboxylic acids with 2-(bicyclo[2.2.1]hept-2-yloxy)ethanol and 2-(5-methylbicyclo[2.2.1]hept-2-yloxy)ethanol in the presence of KU-2-8 cation exchanger (H⁺ form) afforded a series of new compounds containing both ester and ether moieties.     

Regioselective Radical Additions to 7-Oxabicyclo[2.2.1]hept-5-en-2-one

Radical addition to 7-oxabicylco[2.2.1]hept-5-en-2-one ( 1 ) was examined from a regiochemical point of view, and despite the small electronic anisotropy of the double bond, electrophilic radicals were found to add preferentially at C(5) with selectivities of up to 5:1. We also report the first case of an inversion of the regioselectivity of a radical reaction using Lewis acids.     

Double bond isomerization of 5-vinylbicyclo[2.2.1]hept-2-ene to 5-ethylidenebicyclo[2.2.1]hept-2-ene over alkaline earth oxides

All the alkaline earth oxides exhibit activities for double, bond isomerization of 5-vinylbicyclo[2.2.1]hept-2-ene (VBH) to 5-ethylidenebicyclo[2.2.1]hept-2-ene (EBH) at a reaction temperature of 273 K. The order of the activity on the basis of unit weight of catalyst was CaO>MgO>SrO>BaO when compared under optimum pretreatment conditions. The E/Z ratio in the products is determined by the reaction temperature regardless of the type of catalyst; the ratios were 82/18 and 88/12 for the reaction temperatures of 323 and 273 K, respectively.     

Enantioselective synthesis of (+)-5,6-exo-(isopropylidendioxy)-2-phenylsulfonyl-7-oxabicyclo[2.2.1]hept-2-ene

The title compound (+)-1 has been synthesized in four steps from furan and dienophile (+)-3 via an asymmetric Diels–Alder reaction.     

Resolution of 7-oxabicyclo[2.2.1]hept-5-en-2-one via cyclic aminals

High yielding resolution of racemic 7-oxabicyclo[2.2.1]hept-5-en-2-one (±)-1 (`7-oxanorbornenone') via aminal formation with (R,R)-1,2-diphenylethylenediamine 2 is reported. Acidic hydrolysis furnishes the enantiomeric ketones (+)-1 and (−)-1 (≥95% ee). The chiral diamine is efficiently recovered.     

2-Chlorobicyclo[2.2.1]hept-5-ene-2-carboxamide and 2-chlorobicyclo[2.2.1]heptane-2-carboxamide as precursors of bicyclo[2.2.1]hept-5-en-2-one and bicyclo[2.2.1]heptan-2-one: resolution,absolute configuration and hydrogen-bonding properties

The absolute configuration of bicyclo[2.2.1]heptan-2-one has not been correlated with a crystal structure of a chemical precursor. The only chemical correlation available had an ambiguity, which could have reversed the assignment. Herein, we report the resolution of 2-chlorobicyclo[2.2.1]hept-5-en-2-exo-carboxamide on a cellulose triacetate column and the crystal structures of the enantiomerically pure and racemic α-chloroamide. We found the absolute configuration (1R,2R,4R) for the (+)-enantiomer of the α-chloroamide. This compound was converted to (+)-bicyclo[2.2.1]hept-5-ene-2-one by base hydrolysis, and the 5,6-unsaturated compounds converted to the saturated congeners. This is the first unambiguous experimental determination of the absolute configuration of bicyclo[2.2.1]heptan-2-one and of bicyclo[2.2.1]hept-5-ene-2-one. The three crystal structures of 2-chlorobicyclo[2.2.1]hept-5-en-2-exo-carboxamide reported herein reveal H-bonded dimers, with two distinct orientations of the bicyclic portion relative to the carboxamide dimer. In the racemic crystal, each dimer is composed of two enantiomers, and the bicyclic portions have their bridge carbon atom (C-7) on opposite sides of the H-bonded carboxamide dimer moiety. In the enantiomerically pure crystals, the major dimer had both C-7 atoms on the same side of the carboxamide dimer moiety while the minor dimer had the C-7 atoms on opposite sides. The dimers are present in solution, and can be easily monitored.     

Absolute Configuration of 2-Substituted 2-Azabicyclo[2.2.1]hept-5-enes

The diastereoisomeric 2-substituted 2-azabicyclo[2.2.1]hept-5-enes 2 – 4 were prepared by aza-Diels-Alder reaction of cyclopentadiene with the corresponding methaniminium ions. Their relative configurations were deduced using ¹H, ¹H-ROESY experiments, and their absolute configurations were assigned from the crystal structure of the aziridinium derivative (?)- 5 . The absolute configuration of (+)- 1 , i.e. (1R), was assigned by CD spectroscopy.     

Epoxidation of 2-azabicyclo[2.2.1]hept-5-en-3-one

Epoxidation of 2-azabicyclo[2.2.1]hept-5-en-3-one has been performed in high yield with potassium hydrogen persulfate at pH 6, ¹H nmr data indicate an exo stereoconfiguration of the epoxide.     

Synthesis of hexachlorobicyclo[2.2.1]hept-5-enylmethyl haloacetates

Russian Journal of Applied Chemistry - The possibility of preparing hexachlorobicyclo[2.2.1]hept-5-enylmethyl haloacetates by reactions of hexachlorocyclopentadiene with allyl haloacetates was...     

Microwave spectra and dipole moments of bicyclo [2.2.1]-hepta-7-one and bicyclo [2.2.1]hept-2-en-7-one

The microwave spectra of bicycle [2.2.1] hepta-7-one (I), bicyelo [2.2.1] hept-2-en-7-one (II), and exo-5,6-bisdeuteriobicyclo [2.2.1] hept-2-en-7-one (III) have been recorded in the region between 26.5 and 40.0 GHz. The rotational constants in the order A, B, C for the title compounds are 2773.24±0.31, 2301.74±0.04, and 2133.96±0.02 (I); 2979.22±0.08, 2418.60±0.01, and 2235.51±0.01 (II); and 2789.67±0.06, 2385.24±0.01, and 2150.60±0.01 (III). The rotational constants of four vibrationally excited states were also determined for (II). Quadratic Stark effect measurements on the 7₁₆ ← 6₁₅ transition of (I) gave ¦μ_a¦=2.99±0.03. Similar measurements on two 5 ← 4 and 4 ← 3 transitions of (II) gave ¦μ_a¦=2.88±0.03, ¦μ_b¦=0.39±0.03, ¦μ_c¦=0, and ¦μ_total¦=2.91±0.04.     

Chemo- and stereoselective functionalization of 7-oxabicyclo[2.2.1]hept-5-en-2-one with dichloroketene

Dichloroketene adds onto the exo face of the carbonyl group of 7-oxabicyclo[2.2.1]-hept-5-en-2-one giving a dichloro-β-lactone which was transformed into the corresponding 1,3-diol.