13C-NMR-spektren von bicyclo[n.1.0]alkenen

The ¹³C-NMR spectra of some bicyclo[3.1.0]hex-3-en-2-ols and of some bicyclo[3.1.0]hex-3-en-2-ones are described. The bond parameters of bicyclo[3.1.0]hex-3-en-2-one are derived from a structure determination of endo-6-methoxy-1,3,6-triphenylbicyclo[3.1.0]hex-3-en-2-one. The electron density is calculated by the EHT method, and correlated with the ¹³C NMR shifts. For comparison the ¹³C NMR spectrum of a bicyclo[4.1.0]hepta-1,5-dione derivative is analysed. The influence of a cyclopropane system attached to a five-membered and to a six-membered ring is elucidated. Whereas the five-membered ring shows conjugation between the carbonyl group and the cyclopropane system, the same effect is not observed in the six-membered ring analogue. This is explained by the highly rigid structure of the five-membered ring.     

Mass spectra of the bicyclo[n.1.0]alkanes and their halogen derivatives

Conclusions We have systematically studied the mass spectra of the halides of the bicyclo[n.1.O]alkane series (n=4–6), showing the principal mode for fragmentation of these compounds to involve opening of the cyclopropane ring with subsequent elimination of the ring fragments.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 91–97, January, 1977.See [1] also.The authors wish to thank Dr. Tomash (Research Laboratory for Chemical Structure of the Academy of Sciences of the Peoples Republic of Hungary) for having shown the identity of the mass spectra of the isomers of (VI). They would also like to thank O. S. Chizhov for his interest in this work, and B. M. Zolotarev for a valuable discussion.     

Conformation of bicyclo [n.1.0] Derivatives: Part 3. Dioxa- and trioxa-bicyclo[5.1.0] octanes

The conformational geometries and possible interconversion paths for some oxa derivatives of bicyclo[5.1.0] octane have been studied by the molecular mechanics method. The theoretical results are compared with the experimental data for the molecular geometry of bicyclo[5.1.0] octane and 3,5,8-trioxabicyclo[5.1.0] octane, the free energy of activation for cycloheptene epoxide and 3,5-dioxabicyclo[5.1.0] octane, the dipole moments and molar Kerr constants in solution for cycloheptene epoxide, 3,5-dioxa- and 3,5,8-trioxabicyclo[5.1.0] octane.     

Conformation of bicyclo[n.1.0]-compounds: Part I. Bicyclo[5.1.0] octane and cycloheptene epoxide

MINDO/3 quantum-mechanical calculations indicate that the most stable conformations of cis-bicyclo[5.1.0]octane and cycloheptene epoxide are the chair—chair (CC) and boat—chair (BC) conformations, respectively. The possible pathways of interconversion have been studied and are discussed for each molecule. The geometry of trans-bicyclo[5.1.0]-octane has been calculated and a heat of isomerization of 3.8 kcal mol^?1 has been obtained. Theoretical results are compared with the experimental data available.     

Conformation of bicyclo[n.1.0] derivatives: Part 2. Norcarane and cyclohexene epoxide

The conformation al geometries and the possible interconversion paths for bicyclo[4.1.0] heptane (norcarane) and cyclohexene epoxide have been studied by both quantum mechanical and molecular mechanics calculations. The half-chair conformation is the most stable in the two compounds even if conformational equilibria with other forms cannot be excluded. Theoretical results are compared with the experimental data of molecular geometry, heat of formation, rotational constants, dipole moment, molar Kerr constant and proton coupling constants. The results obtained by the force-field method are satisfactory and consequently the extension of the method to derivatives of this kind seems possible.     

Synthesis and properties of gem-(difluorocyclopropyl)amine derivatives of bicyclo[n.1.0]alkanes

[reaction: see text] Generation of difluorocarbene(carbenoid) in the presence of enamines derived from cyclic ketones results in overall insertion of CF2 to produce bicyclic difluorocyclopropylamines. These adducts are very weakly basic, and their thermal stabilities vary markedly with their structures.     

On the photoisomerization of bicyclo[3.2.n]dienones

Two bicyclo[3.2.n]dienones, which differ from one another only by the presence or absence of an O atom as the “n” bridge, show very different pbotoisomerization behavior. Irradation of hexamethyl-8-oxabicyclo[3.2.1]octadienone 12 gives endo-6-acetylpentamethylbicyclo[3.1.0]hexenone 16, probably via an initial [1,3] sigmatropic rearrangement (Scheme 3). In contrast, hexamethylbicyclo[3.2.0]heptadienone 14 photoisomerizes via an initial [3,3]-sigmatropic rearrangement, the isolated product being the relatively stable cyclopentadiene-ketene 26. The methylene analog of 14 (i.e.32) rearranges similarly. giving allene 33 and alkyne 34. The mechanisms of these photoisomerizations are discussed.     

Rearrangements of bicyclo[n.1.1]alkylium cations

In accord with experimental observations, AM1, MNDO and MINDO/3 calculations suggest facile rearrangement pathways available to bicyclo[n.1.1]alkylium cations (n=1,2,3).     

Synthesis of bicyclo[4.n.1]alkanones

Cyclic beta-keto ester monoanions react with 1,4-dihalobutenes to give C-alkylated products which subsequently undergo a stereoselective SN2' O-alkylation reaction to yield functionalized enol ethers. When the starting material was ethyl cyclopentanone carboxylate, the C-alkylated product, treated with a base, directly afforded the functionalized bicyclo[4.2.1]nonanone. The enol ethers were submitted to a flash vacuum thermolysis (FVT) reaction to readily afford functionalized bicyclo[4.n.1]alkanones (n = 3, 4). This reaction sequence was applied to the synthesis of a functionalized tricyclo[7.4.1.0(1,5)]tetradecanone, which represents an analogue to the tricyclic core of ingenol.     

Electrochemical carboxylation of bicyclo[n.1.0]alkylidene derivatives

Electrochemical carboxylation of bicyclo[n.1.0]alkylidene derivatives (ring-fused alkylidenecyclopropanes) in a suitable aprotic solvent using a one-compartment electrochemical cell equipped with a platinum plate cathode and a zinc plate anode under an atmospheric pressure of carbon dioxide afforded either mono- or dicarboxylic acid in moderate to good yields.     

Asymmetric synthesis of bicyclo[n.1.0]alkanes by the enantioselective 1,3-CH insertion reaction of chiral magnesium carbenoids

Treatment of enantiomerically pure 1-chlorovinyl p-tolyl sulfoxides, derived from cyclic ketones and (R)-chloromethyl p-tolyl sulfoxide, with the lithium enolate of tert-butyl carboxylates gave adducts in quantitative yields as single diastereomers. The adducts were treated with i-PrMgCl in toluene to afford optically active bicyclo[n.1.0]alkanes bearing a tert-butyl carboxylate moiety in up to 99% enantiomeric excess through the enantioselective 1,3-CH insertion reaction of the generated chiral magnesium carbenoids. This is the first example of the enantioselective 1,3-CH insertion reaction of magnesium carbenoid.     

Tetrahydrothiophene-catalyzed synthesis of benzo[n.1.0] bicycloalkanes

A catalytic intramolecular cyclopropanation for the preparation of benzobicyclic compounds with [n.1.0] units has been developed. In the presence of 20 mol % of tetrahydrothiophene, the reactions of compounds 2a-2h afford versatile benzo[n.1.0]bicycloalkanes with excellent stereoselectivity in moderate to good isolated yields.     

Conversion of 3,n-dithiabicyclo[n.3.1]alkatrienes to bicyclo[n.3.1]alkapentaenes

The application of the Ramberg-Backlund reaction in the conversion of several 3,n-dithiabicyclo[n.3.1]alkatrienes to the corresponding bicyclo[n.3.1]alkapentaenes is reported. Proton magnetic resonance and ultraviolet spectra were utilized in the overall characterization of bicyclo[8.3.1]tetradeca-2,8,10,12,1(14)-pentaene, bicyclo[9.3.1]pentadeca-2,9,11,1(15)-pentaene, and their precursors. The final step in the synthesis was a Ramberg-Backlund of bis-α,α′-chloro sulfone. The intermediate, 2-chloro-3-thiabicyclo[9.3.1]pentadeca-9,11,13,1(15)-tetraene 3,3-dioxide, was isolated and characterized. The structure and stability of the bridged α,α′-dichloro sulfide intermediates were examined.