Intramolecular lactone annulation of activated acids with Mn(III)

Intramolecular lactone annulation of activated carboxylic acids onto olefins by manganese(III) acetate yields bicyclo[3.3.0] and [4.3.O]lactones.     

L'importance de la presence de l'oxygene en position-7 dans les reactions des alkylmagnesiens secondaires avec les anhydrides tricycliques pontes.

The reaction of secondary alkylmagnesium bromides with endo and exo bicyclo-[2.2.1]hept-5-ene-2,3-dicarboxylic anhydrides lead at the corresponding ketoacids whereas with the 7-oxa exo bicyclo[2.2.1]hept-5-ene-2,3 dicarboxylic anhydride produced only the monosubstituted lactones.     

Studies on transannulation reactions across a nine-membered ring: the synthesis of natural product-like structures

A series of diverse natural product-like structures have been synthesised by the use of a number of novel transannulation reactions across a cyclononene ring. Transannular cyclisations through oxygen functionality have generated a number of bicyclo[5.3.1]systems containing bridged cyclic ethers and bicyclo[5.2.2]lactones, as well as a tetrahydrofuran-containing bridged analogue of hexacyclinic acid. An unprecedented Br?nsted acid mediated transannular cyclisation between proximal carbons generated bicyclo[4.3.0]nonanes which form the core of the pinguisane and austrodorane families of sesquiterpenoids. In all cases the key factor that determined the mode of reactivity was the conformation of the nine-membered ring and the distance between the reacting centres.     

Stereoisomeric carboxamides of the bicyclo[2,2,1] heptene series in the epoxidation reaction

The epoxidation of isomeric carboxamides of the bicyclo[2,2,1]heptene series has been studied; in the case of exo-carboxamides it leads to expoxides, and in the case of endo-carboxamides to tricyclic lactones.     

Azulenes and related substances—XI A new azulene synthesis—azulene, 1-methyl-2-methyl- and 1, 3-dimethylazulene

The polyphosphoric acid induced intramolecular acylation of lactones has been applied to the synthesis of the bicyclo [0,3,5] decane system, and the preparation of azulene, 1-methyl-, 2-methyl- and 1,3-dimethylazulene is reported.     

Stereoselective synthesis of bicyclic lactones by annelation with functionalized orthoesters

An efficient two-step annelation of functionalized orthoesters with trimethylsilyloxyfuran derivatives, which delivers suitably decorated bicyclo[3.n.0]lactones in high overall yields and with complete diastereocontrol of up to three contiguous stereocenters, is reported.     

Preparation and aluminum trichloride-induced cationic rearrangements of bicyclo[2.2.0]hexene carboxylic esters

Reaction between the tetramethyl[4]annulene aluminum trichloride σ-complex and α, β-alkenic esters gave the corresponding 1,4,5,6-tetramethylbicyclo[2.2.0]hex-5-one-2-endo-carboxylic esters. AlCl₃-induced cationic rearrangements of these bicyclic esters yielded a number of bicyclo[3.1.0]hexene carboxylic esters and related lactones which were isolated and identified. The isomerization seems to proceed via stereospecific endo protonation and subsequent rearrangement to 2-methoxycarbonyl-1,4,5,6-exo-tetramethylbicyclo(3.1.0]hex-4-yl carbocations.     

Novel bicyclo[2.2.2]lactones from a facile condensation of dibenzoylethylene with arylacetonitriles

Several novel bicyclo[2.2.2]lactones were synthesized from a facile one-pot reaction by the condensation of dibenzoylethylene and an arylacetonitrile in basic medium. The reaction proved to be convenient and gives high yield. The structure of the reaction products was established on the basis of their proton and carbon-13 nuclear magnetic resonance, and infrared spectral data as well as their elemental analysis.     

Microbial Baeyer-Villiger Oxidation of Ketones by Cyclohexanone and Cyclopentanone Monooxygenase – A Computational Rational for Biocatalyst Performance

Summary. Recombinant Escherichia coli overexpressing Pseudomonas sp. NCIMB 9872 cyclopentanone monooxygenase (CPMO, EC 1.14.13.16) and Acinetobacter sp. NCIMB 9871 cyclohexanone monooxygenase (CHMO, EC 1.14.13.22) have been utilized in whole-cell Baeyer-Villiger biotransformations of prochiral bicycloketones. A significant difference in substrate acceptance and stereoselectivity was observed for bicyclo[3.3.0] and bicyclo[4.3.0] substrates. A plausible mechanism of these transformations was established by means of high level DFT/B3LYP calculations suggesting an essential difference in electronic requirements for a successful enzymatic conversion, which was similarly encountered in recombinant whole-cell mediated biooxidations. Some of the lactones produced in the biocatalytic Baeyer-Villiger oxidation represent key intermediates for the synthesis of indole alkaloids.     

Skeletal rearrangements of bicyclo[2.2.2]lactones: a short and efficient route towards Corey’s lactone

The application of a unique tandem radical-initiated, Brönsted acid-catalysed, skeletal rearrangement of bicyclo[2.2.2]lactones provides a novel route towards Corey’s lactone 2. The strategy also features a high-pressure promoted inverse electron-demand Diels-Alder (IEDDA) reaction of 3-carbomethoxy-2-pyrone (3-CMP), which proceeds with complete regio- and diastereocontrol.     

Reactions stereoselectives des alkylmagnesiens secondaires avec les anhydrides et lactones rigides

High stereoselectivity was observed in the reactions of secondary alkylmagnesium compounds with bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride $\text{1}$ and lactone 2 leading respectively to the formation of $\text{trans}$ diastereomeric lactones and $\text{erythro}$ primary-secondary diols.     

Cycloaddition between electron-deficient pi-systems, photochemical and radical-induced reactions: a novel, general, and stereoselective route to polyfunctionalized bridged bicyclo[2.2.2]octanes, bicyclo[3.3.0]octanes, bicyclo[4.2.0]octanes, and tricyclo[4.3.1.0(3,7)]decanes

A novel, general, and stereoselective route to functionalized bridged bicyclo[2.2.2]octanes, bicyclo[3.3.0]octanes, bicyclo[4.2.0]octanes, and tricyclo[4.3.1.0(3,7)]decanes has been described. Various functionalized and substituted bicyclo[2.2.2]octanes endowed with a beta,gamma-enone chromophore were synthesized via cycloaddition of in situ generated cyclohexa-2,4-dienones with electron-deficient 2pi partners and manipulation of the resulting adducts. Triplet sensitized irradiation of bridged bicyclooctenones led to synthesis of bicyclo[3.3.0]octanoids, whereas the direct irradiation furnished bicyclo[4.2.0]octanes in stereoselective fashion as a result of modulation of reactivity in excited states. Further, manipulation of the adducts led to appropriately appended and functionalized bicyclo[2.2.2]octanes that upon radical induced cyclization provided an efficient and stereoselective route to the tricyclo[4.3.1.0(3,7)]decane (isotwistane) framework of pupukeananes.     

Oxidative Dearomatization: Synthesis of Functionalized Bicyclo[2.2.2]octenones,Sigmatropic Shift in Excited State,and Radical-Induced Cleavage of Cyclopropane Ring

Synthesis of novel bicyclo[2.2.2]octenones endowed with a β,γ-enone system in which γ-carbon is substituted with an electron-withdrawing group from simple aromatics is described. Oxa-di-pi-methane reaction of bicyclo[2.2.2]octenones to functionalized bicyclo[3.3.0]octanes and their transformation to bicyclo[3.2.1]octane framework are also presented.     

Synthesis of 1,10-phenanthrolines fused with bicyclo[3.3.0]octane and bicyclo[3.3.1]nonane frameworks

Reactions of bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.0]octane-3,7-dione with 8-amino-7-quino-linecarbaldehyde under basic conditions led to fused nonplanar compounds with one or two 1,10-phenanthroline moieties. The novel heterocyclic systems bicyclo[3.3.1]nonano[2,3-b]bis[1,10]-phenanthroline, cis-bicyclo[3.3.0]octano[3,2-b:7,6-b']bis[1,10]phenanthroline, bicyclo[3.3.1]nona-no[2,3-b:6,7-b']bis[1,10]phenanthroline, and 8H-9,16-methanoindolo[2',3':5,6]cycloocta[1,2-b]bis-[1,10]-phenanthroline have been synthesized and characterized.     

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.     

Experimental and computational bridgehead C-H bond dissociation enthalpies

Bridgehead C-H bond dissociation enthalpies of 105.7 ± 2.0, 102.9 ± 1.7, and 102.4 ± 1.9 kcal mol(-1) for bicyclo[2.2.1]heptane, bicyclo[2.2.2]octane, and adamantane, respectively, were determined in the gas phase by making use of a thermodynamic cycle (i.e., BDE(R-H) = ΔH°(acid)(H-X) - IE(H(·)) + EA(X(·))). These results are in good accord with high-level G3 theory calculations, and the experimental values along with G3 predictions for bicyclo[1.1.1]pentane, bicyclo[2.1.1]hexane, bicyclo[3.1.1]heptane, and bicyclo[4.2.1]nonane were found to correlate with the flexibility of the ring system. Rare examples of alkyl anions in the gas phase are also provided.     

Bicyclo[3.3.1]nonane and its derivatives—IV : Reactions of some carbonyl derivatives of bicyclo[3.3.1]nonane with diazomethane

The reaction of bicyclo[3.3.1]nonane-2,6-dione with diazomethane in situ does not lead to the homologous bicyclo[4.3.1]decane-2,7-dione, but mainly to tricyclo[4.4.0.0^2,9]decan-9-ol-5-one. The structure of the latter was confirmed by the proton NMR spectra measured with an addition of Eu(DPM)₃, A mixture of tricyclo[4,4.0.0^2,9]decan-9-ol-5-one and bicyclo[4.3.1]decane-2,7-dione results when solutions of diazomethane are used. The reaction of bicyclo[3.3.1]nonane-2,6-dione monoethyleneacetal with diazomethane in situ yields predominantly bicyclo[4.3.1]decane-2,7-dione. Under the same conditions bicyclo[3.3.1]nonan-2-one gives with diazomethane in situ only bicyclo[4.3.1]decan-2-one.     

Carbon-13 chemical shifts of bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane derivatives

¹³C chemical shifts of more than fifty bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane derivatives (hydrocarbons, alcohols, ketones and esters) have been determined. The usefulness of ethyl derivatives for the assignment of close ¹³C chemical shifts in bicyclic methyl derivatives is shown both for the bicyclo[3.2.1]octane and bicyclo[2.2.1]heptane series. Comparison of substituent effects on α-, β-, γ- and δ-carbons in both series of compounds shows remarkable differences in steric interactions. In contrast to the rigid bicyclo[2.2.1]heptane system, both chair and boat conformations can be predominant in the bicyclo[3.2.1]octane series with the conformationally flexible 6-membered ring.     

Determination de la configuration absolue de quelques derives du bicyclo[2.2.2]octane: Utilisation comparee de la regle des octants et de la methode d'horeau

A series of bicyclo[2.2.2]octane derivatives whose absolute configurations are known through chemical correlations with confirmed reference products (bicyclo[2.2.2]octanol, bicyclo[2.2.2]octene carboxylic acid) have been prepared.     

Electronic and Steric Structure of Thermal Isomerization Products of 1-Methyltricyclo[4.1.0.02,7]heptane Radical Cation

Distributions of the positive charge and unpaired electron in stable conformers of the thermal isomerization products of 1-methyltricyclo[4.1.0.02,7]heptane radical cation, having bicyclo[3.1.1]heptane, bicyclo[4.1.0]heptane, bicyclo[3.2.0]hept-6-ene, and 1,3-cycloheptadiene skeletons, were estimated by the PM3 semiempirical method.