The electronic structure of bicyclo [2.2.1] heptane and of bicyclo [2.2.2] octane

An ab initia SCF-LCAO-MO study of bicyclo [2.2.1] heptane(I) and of bicyclo [2.2.2] octane(II) has been performed. The electronic structure and the nature of the molecular orbitals and of the bonds have been analyzed. Interactions between fragment orbitals may be recognized. The bridgehead C-H bonds interact dominantly “through-space” in I and “through-bond” in II. Some relations between electronic structure and molecular properties are discussed.     

13C NMR spectroscopy of some 3- and 7-substituted bicyclo[3.3.1]nonanes

The ¹³C NMR spectra of a series of 3,7-substituted bicyclo[3.3.1]nonane derivatives are examined. Taken into account substituent influences, the ¹³C chemical shifts appear to be diagnostic for the conformation of the bicyclo[3.3.1]nonane derivative.     

13C NMR spectra of tricyclo[4.2.1.02,5]nonanes and tetracyclo[5.4.1.02,6.08,11]dodecanes

The ¹³C NMR spectra of tricyclo[4.2.1.0^2,5]nonanes and tetracyclo[5.4.1.0^2,6.0^8,11]dodecanes and their dimethyl derivatives were measured to demonstrate the four-membered ring annelation effects on the bicyclo[2.2.1]heptane skeleton, and the steric δ-syn effects of the methyl groups attached to the four-membered ring on the bridge carbons in these systems.     

Simple NMR method for assigning relative stereochemistry of bridged bicyclo[3.n.1]-2-enes and tricyclo[7.n.1.0]-2-enes

The stereochemistry of syn and anti-forms of bridged bicyclo[3.n.1]-2-ene, tricyclo[7.n.1.0]-2-ene (n=1-3) and bicyclo[4.3.1]dec-7-ene derivatives can be assigned from the ¹³C chemical shift difference of the double bond. Both syn-9-R-bicyclo[3.3.1]non-2-enes and syn-13-R-tricyclo[7.3.1.0^2,7]tridec-2(7)-enes have a large shielding difference between sp² carbons, while the corresponding anti-forms have a smaller one. In contrast, 8-R-bicyclo[3.2.1]oct-2-enes and 12-R-tricyclo[7.2.1.0^2,7]dodec-2(7)-enes have an inverse correlation. The reason of this specificity is the influence of the γ-gauche effect on the chemical shift of C(2) atom. The GIAO theory has been applied to investigate the ¹³C chemical shifts. The conformational equilibrium in the formamide group of 13-formylamino-tricyclo[7.3.1.0^2,7]tridec-2(7)-enes has been studied.     

Trimethylsilyl group directed wagner-meerwein rearrangement of bicyclo[2.2.2]octan-2-ol derivatives

Trimethylsilyl group substituted bicyclo[2.2.2]octane derivatives were synthesized and subjected to TMS group directed Wagner-Meerwein rearrangement to give bicyclo[3.2.1]octene derivatives in high yields.     

A New Route to the Synthesis of 7-Functionalised Bicyclo[2.2.1]Heptane Derivatives

A new route to the synthesis of 7-functionalised bicyclo[2.2.1]heptane derivatives having a bridgehead alkoxy group is described involving Wolff rearrangement of α-diazo ketone in a bicyclo[2.2.2]octane derivative.     

13C NMR spectra of polycyclic compounds: Stereochemistry of trimers of bicyclo[2.2.1]heptadiene

¹³C NMR spectra have been obtained for six isomers of bicyclo[2.2.1]heptadiene (norbornadiene) trimers, and a complete stereochemical assignment of these isomers has been made by means of a computer-assisted calculation of chemical shifts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1973–1978, September, 1990.     

Long-range deuterium isotope effects on fluorine-19 chemical shifts of 4-substituted bicyclo[2.2.2]octyl- and bicyclo[2.2.1]heptyl-1-fluorides : Deuterium as a substituent

²H/¹H isotope effects on the ¹⁹F chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl and bicyclo[2.2.1]hept-1-yl fluoride are significantly shielding and deshielding, respectively. This result is consistent with deuterium being viewed as an $\text{electronegative}$ substituent relative to hydrogen when attached to an sp³ hybridised carbon.     

Intramolecular hydrogen abstraction promoted by N-radicals: synthesis of chiral 7-oxa-2-azabicyclo[2.2.1]heptane and 8-oxa-6-azabicyclo[3.2.1]octane ring systems

Homochiral 7-oxa-2-azabicyclo[2.2.1]heptane and 8-oxa-6-azabicyclo[3.2.1]octane ring systems can be synthesized by reaction of specifically protected phosphoramidate derivatives of carbohydrates with (diacetoxyiodo)benzene or iodosylbenzene and iodine. The reaction mechanism goes through homolytic fragmentation of a hypothetical iodoamide intermediate. The N-radicals so generated participate in an intramolecular hydrogen abstraction reaction (IHA) to give the aforementioned bicycles.     

Unusual carbon shielding effects of cyclopropanes and double bonds in strained bicyclo[3.1.0]hexanes and cyclopentenes

Carbon-13 shieldings and one-bond ¹³C? H coupling constants of bicyclo[2.1.1]hexane, bicyclo[2.1.1]hex-2-ene, tricyclo[3.1.1.0^2,4]heptane and benzvalene are presented and compared to the data of related compounds. If a bicyclo[3.1.0]hexane system is part of a rigid skeleton, the cyclopropane ring exerts specific γ substituent effects of two kinds. In the case of the bicyclohexane boat form an upfield shift of the C-3 signal is observed and in the case of the chair form a downfield shift of 15–20 ppm. Compared to the corresponding cyclopentanes the double bond in strained cyclopentenes causes downfield shifts of the C-4 absorption. This effect increases with increasing strain, reaching a 45.9 ppm maximum in benzvalene. Hence it is the only known bicyclo[1.1.0]butane having a reversed order of carbon shieldings. The downfield shifts are explained by means of simple orbital interaction schemes.     

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.     

NMR isotope shifts in the 2-methyl-2-bicyclo[2.1.1]hexyl cation and related systems

NMR isotope shifts at ¹³C nuclei due to deuteriation in the 2-methyl-2-bicyclo[2.1.1]hexyl cation are reported. Comparisons are made to the 2-methyl-2-bicyclo[2.2.1]heptyl and 2-methyl-2-bicyclo[2.2.2]octyl cations, and also to neutral molecules containing the bicyclo[2.1.1]hexyl framework. The combination of isotope effects with temperature dependence of ¹³C chemical shifts allows predictions of the shapes of the energy surfaces along the bending coordinate corresponding to bridging in these cations.     

Synthesis of Bridged Bicyclic Molecules using Halocarbenes. Derivatives of bicyclo[4.2.1]nonane

The addition of dichlorocarbene (generated by the interaction of sodium methoxide and ethyl trichloroacetate) to bicyclo[3.2.1]oct-2-ene, its 3-chloro and exo-3,4-dichloro derivatives gives the exo 1 : 1 adducts in yields of 94, 89 and 48%. By suitable chemical reactions of these adducts, convenient syntheses of bicyclo[4.2.1]nona-2,4-diene and bicyclo[4.2.1]non-3-ene, together with their monochloro, dichloro and trichloro derivatives are obtained. Bicyclo[4.2.1]-nonan-3-one is also obtained from bicyclo[4.2.1]non-3-ene in a synthesis starting from the readily available 5-hydroxymethylnorborn-2-ene in an overall yield of 20%.     

Carbon-13 NMR spectra of solid bicyclo[3. 3. 1]nonan-9-one. Conformational studies in the solid state

Carbon-13 NMR spectra of solid polycrystalline bicyclo[3.3.1]nonan-9-one and adamantanone have been measured at 315K. The relatively narrow ¹³C linewidths observed for these solids, together with measured spin-lattice relaxation times, indicate that both these solids are orientationally disordered. Observed ¹³C chemical shifts of solid bicyclo[3.3.1]nonan-9-one indicate a twin-chair conformation for the two cyclohexanone rings.     

Polyesters containing bicyclo[2.2.2]octane and bicyclo[3.2.2]nonane rings

Polyesters containing bicyclo[2.2.2]octane and bicyclo[3.2.2]nonane rings are prepared from 1,4-bis(carboethoxy)bicyclo[2.2.2]octane, 1,4-bis(hydroxymethyl)bicyclo[2.2.2]-octane and the 1,5-disubstituted bicyclo[3.2.2]nonane analogs. These polyesters are compared to the related polymers containing 1,4-phenylene and trans-1,4-cyclohexylene rings in terms of their melting point, thermal stabilities and oxidative stabilities. The lower symmetry of the bicyclo[3.2.2]nonane ring produces lower-melting polymers than the other ring systems. The remaining three rings are approximately equivalent in their effect on the melting point of a polymer provided that no more than one bicyclo[2.2.2]octane ring is present per polymer repeat unit. Two such rings produce a highermelting polymer than any other combination. Both the thermal and oxidative stabilities of the polyesters is improved by the presence of the bicyclo rings. This is attributed to the rings providing an approximation of a ladder polymer.     

Biohydroxylation d'un aza-2 bicyclo [2.2.1] heptane

Biohydroxylation with Beauveria sulfurescens of the 5-exo position of the 2-aza bicyclo [2.2.1] heptane ring system gives rise to a precursor of carbocyclic 2-deoxy nucleosides.     

Unusual ring-chain tautomerism in bicyclo[4.2.0]octane derivatives

A new type of ring-chain tautomerism, which consists of the reversible conversion of bicyclo[4.2.0]octane derivatives into trisubstituted enamines was found and studied by ¹H NMR spectroscopy. The starting materials were prepared by the stereoselective reaction of (E)-3,3,3-trichloro-1-nitropropene with cyclohexanone enamines.     

Chiral synthons from α-pinene: enantioselective syntheses of bicyclo[3.3.0] and [3.2.1]octanones

Enantioselective syntheses of bicyclo[3.3.0]octan-3-one, bicyclo[3.2.1]octan-3-one and bicyclo[3.2.1]octan-2-one derivatives were accomplished by employing a chiron based approach, using intramolecular rhodium carbenoid C–H insertion, acid catalysed cyclisation of α-diazo ketone and intramolecular type II carbonyl ene reactions as key steps.     

Regiocontrolled synthesis of bicyclo[3.2.1]octane derivatives by cuprate addition and intramolecular acylation

Copper-catalysed reaction of 4-butenylmagnesium bromide with cyclohexenones (2) and (5) occurs with intramolecular acylation of the intermediate enolate to give bicyclo[3.2.1]octane derivatives (4) and (6).     

The bromination of bicyclo[3.2.1]octa-2,6-diene with N-bromosuccinimide

The bromination of bicyclo[3.2.1]octa-2,6-diene (3) by NBS does not follow the familiar free-radical course but proceeds through the cyclopropylcarbinyl cation 7. 7 can be trapped by addition of small amounts of methanol. The bicyclo[3.2.1]octa-2,6-dien-4-yl radical is involved in the reduction of exo-6-bromotricyclo [3.2.1.0^2,7]oct-3-ene by tributyltin hydride.