Zur Konformation des Bicyclo[2.2.2]octan-Systems

Crystals of bicyclo [2.2.2] octane-1, 4-dicarboxylic acid are monoclinic, a = 6.01 Å, b = 16.73 Å, c = 10.29 Å, β = 115.08°, space group P2₁/c, with 4 molecules in the unit cell. The structure was solved with the help of direct methods and refined by full-matrix least-squares analysis of the three-dimensional intensity data. Within experimental error the bicyclo [2.2.2]-octane (BCO) skeleton has apparent D_3h-symmetry, corresponding to the totally eclipsed conformation. Analysis of the thermal ellipsoids in terms of the translational and rotational motion of the BCO skeleton leads to an r.m.s. amplitude of 5.9 ± 0.2° for rotation about the threefold axis. On the assumption that the bond lengths remain effectively constant during a torsional vibration of BCO, the potential energy surface has been calculated for a range of semi-empirical potential functions. These calculations show that the energy minimum may be slightly displaced from D_3h symmetry, but if so the barrier between the two such equivalent minima is only about 0.1 kcal mole^?1. The energy eigenvalues and eigenfunctions for a typical variation of potential energy vs torsion angle have been calculated. From the form of the eigenfunction of the ground vibrational state we conclude that BCO has effective D_3h symmetry at all temperatures as far as diffraction methods are concerned.     

The Reaction of Difluorocarbene with Bicyclo[2.2.2]octadiene

The addition of difluorocarbene to bicyclo[2.2.2]octa-2,5-diene gave the exo and endo 1:1 cyclopropane adducts. In contrast to norbornadiene, no homo-1,4 adduct was formed. The adducts were thermally stable under the conditions of their formation and separation (<170°). However, smooth equilibration was achieved on heating at 250° for 36 h. The same mixture resulted from either isomer. At 250° ΔΔG = 1.83 kcal/mol; the endo isomer being the more stable. Heating to higher temperatures caused decomposition, rather than further reaction to the intramolecular [2+2]cyclization products. The kinetic and thermodynamic product compositions were essentially the same on extrapolating to the same temperature, viz. endo/exo = 19–22 at 25°. The mechanisms by which the cyclo-addition and the stereomutation of the cis-fused cyclopropane moiety occur are discussed.     

Synthesis of Novel Triacetal Trioxa-Cage Compounds by Ozonolysis of Bicyclo[2.2.1]Heptenes and Bicyclo[2.2.2]Octenes

Several novel triacetal trioxa-cage compounds 11a-11g, 13, 15, 17 and 19 are synthesized in a short sequence. Ozonolysis of bicyclo[2.2.1]heptenes 4a-4c, 8a-8c, 10a, 10b and 14 in dichloromethane at ?78 °C followed by reduction with dimethyl sulfide gave triacetal oxa-cages 11a-11g, 13 and 15 in moderate yields, respectively. Ozonolysis of bicyclo[2.2.2]octenes 16 and 18 under the same reaction conditions gave triacetal oxa-cages 17 and 19 in moderate yields, respectively.     

Synthesis of Optically Active endo,endo Bicyclo[2.2.2]octane-2,5-diol, Bicyclo[2.2.2]octane-2,5-dione, and Related Compounds

Optically active C(2)-symmetric (1S,2S,4S,5S)-bicyclo[2.2.2]octane-2,5-diol ((+)-12; 98% ee) and several selectively protected optically active intermediates useful for synthetic transformations were synthesized via a 1,2-carbonyl transposition route starting from the easily available optically active (1R,4S,6S)-6-hydroxybicyclo[2.2.2]octan-2-one ((-)-2). The synthetic route also allowed the preparation of optically active (1S,4S)-bicyclo[2.2.2]octane-2,5-dione ((+)-14; 98% ee).     

Neighboring Group Participation in a Regio- and Stereoselective Chlorination of a Bicyclo[2.2.2]octanone

The zinc chloride-mediated acetylation of the optically active silyl enol ether 2a gave the beta-diketone 3a (48%) together with the regio- and stereoselectively chlorinated compound 4 (27%). The yield of 4 increased to 70% by starting from the O-acetyl derivative 2c. The chlorination most likely occurs via neighboring group participation by the endo acetoxy group.     

Die Synthese von 4-substituierten Bicyclo[2.2.2]oct-1-yl-p-nitrobenzolsulfonaten

Synthesis of 4-Substituted Bicyclo[2.2.2]oct-1-yl-p-Nitrobenzenesulfonates The syntheses of the 4-substituted bicyclo[2.2.2]oct-1-yl-p-nitrobenzenesulfonates 1a–2s are described.     

Cubane,Bicyclo[1.1.1]pentane and Bicyclo[2.2.2]octane: Impact and Thermal Sensitiveness of Carboxyl-, Hydroxymethyl- and Iodo-substituents

With the burgeoning interest in cage motifs for bioactive molecule discovery, and the recent disclosure of 1,4-cubane-dicarboxylic acid impact sensitivity, more research into the safety profiles of cage scaffolds is required. Therefore, the impact sensitivity and thermal decomposition behavior of judiciously selected starting materials and synthetic intermediates of cubane, bicyclo[1.1.1]pentane (BCP), and bicyclo[2.2.2]octane (BCO) were evaluated via hammer test and sealed cell differential scanning calorimetry, respectively. Iodo-substituted systems were found to be more impact sensitive, whereas hydroxymethyl substitution led to more rapid thermodecomposition. Cubane was more likely to be impact sensitive with these substituents, followed by BCP, whereas all BCOs were unresponsive. The majority of derivatives were placed substantially above Yoshida thresholds—a computational indicator of sensitivity.     

Protonenresonanzspektroskopische Untersuchungen an Bicyclo [2.2.1]heptan- und Bicyclo[2.2.2]octan-Derivaten: Einfluss von Substituenten auf die chemische Verschiebung

The influence of substituents on the chemical shifts of protons in bicyclo[2.2.1]-heptanes and bicyclo[2.2.2]octanes is discussed. A linear correlation between the change in chemical shift of a proton, due to a neighbouring methyl group, and the distance between this proton and the methyl group is obtained.     

The Non-planarity of the Bicyclo[2.2.1]hept-2-ene Double bond. Crystal Structures of Bicyclo[2.2.2]oct-2-ene,Bicyclo[2.2.1]hept-2-ene,and Bicyclo[2.1.1]hex-2-ene Systems

The crystal structures of (1R,4R,5S,8S)-9,10-dimethylidentricyclo[6.2.1.0^2,7]undec2(7)-ene-4,5-dicarboxylic anhydride ( 3 ), (1R,4R,5S,8S)11-isopropylidene-9,10-dimethylidenetricyclo[6.2.1.m^2,7]undec-2(7)-ene-4,5-dicarboxylic anhydride ( 6 ), (1R,4R,5S8S)-9,10-dimethylidenetricyclo[6.2.2.0^2,7]dodec-2(7)-ene-4,5-dicarboxylic anhydride ( 9 ), (1R4R5S8S)-TRICYCLO[6.2.2.0^2,7]dodeca-2(7), 9-diene-4,5-dicarboxylic anhydride ( 12 ) and (4R,5S)-tricyclo[6.1.1.0^2.7]dec-2(7)-ene-4,5-dicarboxylic acid ( 16 ) were established by X-ray diffraction. The alkyl substituents onto the endocyclic bicyclo[2.2.1]hept-2-ene double bond deviate from the C(1), C(2), C(3), C(4), plane by 13.5°4 in 3 and by 13.9° in 6 , leaning toward the endo-face. No such out-of-plane deformations were observed with the bicyclo[2.2.2]oct-2-ene derivatives 9 and 12 . The exocyclic s-cis-butadiene moieties in 3, 6 and 9 do not deviate significantly from planarity. The deviation from planarity of the double bond n bicyclo[2.2.1]hept-2-ene derivatives and planarity in bicyclo[2.2.2]oct-2-ene analogues is shown to be general by analysis of all known structures in the Cambridge Crystallographic Data File. The non-planarity of the bicyclo[2.2.1]hept-2-ene double bond cannot be attributed only to bond-angle deformations which would favour rehybridizatoin of the olefinic C-atoms since the double bond in the more strained bicyclo[2.1.1]hex-2-ene drivative 16 deviates from planarity by less than 4°.     

The Quest for Bridgehead Bridgehead Dications with Bicyclo[2.2.2]octyl Skeletons

It is predicted by MINDO/3 calculations that the 1,5-trishomobarrelenediyl dication 4 would be as much stabilized over the bicyclo[2.2.2]octanediyl dication 3 as the monocation 7 -H is energetically favored over the hypothetical 1-bicyclo[2.2.2]octyl 10 -H. In spite of this, the bridgehead cations generated from the 1,5-dihalo-trishomobarrelenes 6 -F, 6 -Cl, 6 -Br, and 6 -I and from the 1,5-diol 6 -OH under long-lived ion conditions were only the 5-substituted monocations 7 -F, 7 -Cl, 7 -Br, 7 -I, and 7 -OH, respectively, unequivocally identified by their ¹H- and ¹³C-NMR spectra as well as quenching products. Although there is efficient charge delocalization in 7 -X, as revealed by the ¹³C-chemical shifts, the lack of formation of the bridgehead bridgehead dication 4 is not due to an unforeseen destabilization by the three α-annellated cyclopropyl groups. Even the 1,5-dichlorotetracyclo[3.3.2.0^2,4.0^6,8]decanes 17 -Cl₂ and 19 -Cl₂ and 1,5-dichlorotricyclo[3.2.2.0^2,4]nonane 12 -Cl₂ with only two and one α-cyclopropyl groups, respectively, gave the bridgehead monocations 18 -Cl, 20 -Cl, and 13 -Cl, respectively.     

A Convenient Preparation of a Bicyclo[3.3.3]undecane Derivative Containing Heteroatoms Through a Rearrangement Step

A convenient method for the preparation of a bicyclo[3,3,3]undecane derivative via the Beckmann rearrangement of bicyclo[3,3,2]decane-9-one is described.     

Highly functionalized Bicyclo[2.2.2]octenone-fused [60]fullerenes from masked o-benzoquinones and C(60)

[reaction: see text] The Diels-Alder reactions of masked o-benzoquinones (MOBs) with [60]fullerene, affording novel and highly functionalized bicyclo[2.2. 2]octenone-fused [60]fullerene derivatives, are described.