Synthesis of bridgehead hydroxy bicyclo[2.2.2]octane derivatives

Two independent synthetic routes, starting from 1,3-cyclohexadione, toward the 4-hydroxy bicyclo[2.2.2]octane-2,6-dione derivative 3 are described.     

Comparative studies of three- and four-ring mesogenic esters containing p-carborane, bicyclo[2.2.2]octane, cyclohexane, and benzene

Twelve esters were prepared from pentyl-substituted p-carborane, bicyclo[2.2.2]octane, cyclohexane, and benzene carboxylic acids and three substituted phenols. The mesogenic properties of the series of esters were examined using thermal analysis and optical microscopy. The relationships between structure and mesogenic properties were analysed by comparison of the series of homostructural esters. Thus, the effects of variation of the carboxylic acid structure, introduction of fluorine into the phenol part, and replacement of the central phenyl ring with the -CH₂CH₂- group on the stability of mesophases and their widths were investigated. In general, carborane derivatives exhibit broad nematic phases and narrow SmA phases, while other derivatives demonstrate rich smectic and soft crystal polymorphism.     

Synthesis of novel spiro-cyclohexene bicyclo[2.2.2]octane derivatives

A methodology for the synthesis of novel spiro-cyclohexene bicyclo[2.2.2]octane derivatives, including Claisen rearrangement and ring-closing metathesis (RCM) as key synthetic steps, is described.     

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.     

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.     

Enantioselective synthesis of bridgehead hydroxyl bicyclo[2.2.2]octane derivatives via asymmetric allylindation

A recent new strategy for the transformation of mono-dioxolane protected 1,3-cyclohexadione into bridgehead hydroxyl bicyclo[2.2.2]octane derivatives, based on allylindation followed by ozonolysis and intramolecular aldol addition, was modified to include asymmetric allylindation. This enabled the first enantioselective synthesis of (1R,4R,6S)-endo-4-(tert-butyl-dimethyl-silyloxy)-6-hydroxy-bicyclo[2.2.2]octan-2-one and (1S,4S,6R)-endo-4-(tert-butyl-dimethyl-silyloxy)-6-hydroxy-bicyclo[2.2.2]octan-2-one in high enantiomeric excess. Issues concerning the non-reproducibility of the asymmetric allylindation were also addressed.     

Asymmetric sequential Michael reaction: Synthesis of optically active bicyclo[2.2.2]octane derivatives

The sequential Michael reaction of (S)-4,5-di-O-isopropylidenepent-2- enoate and with lithium enolate afforded diastereo- and enantioselectively bicyclo[2.2.2]octane and (or ), respectively. The adducts were efficiently converted into both enantiomeric keto aldehydes (−)- and (+)- .     

Synthesis of crownophane with the bicyclo[2.2.2]octane core

Russian Chemical Bulletin -     

Conformational effects on mesophase stability: numerical comparison of carborane diester homologous series with their bicyclo[2.2.2]octane,cyclohexane and benzene analogues

Three series of diesters of 4‐alkoxyphenols containing 12‐vertex p‐carborane (1A[n], n = 1–22), 10‐vertex p‐carborane (1B[n], n = 1–12) or bicyclo[2.2.2]octane (1C[n], n = 1–12) as the central structural element were prepared and investigated by optical and calorimetric methods. All carborane diesters exhibited exclusively nematic behaviour, whereas the carbocyclic analogues 1C[n] and also cyclohexane (1D[n]) and benzene (1E[n]) derivatives, showed early onset of SmA phase and complete disappearance of nematic behaviour. The isotropic transition temperatures, T _MI, for the five series of mesogens were analysed numerically using a three‐parameter exponential function. The resulting limiting values, T _MI(∞), provided a quantitative assessment of the central element ability to support the mesogenic state. They demonstrated that, whereas the T _MI(∞) values for the carbocycles, C, D, and E, are around 125°C, for carboranes A and B this value is 70±2°C and 49±19°C, respectively. Two types of comparative analysis of trends in T _MI relative to those of the terephthalate series 1E[n] demonstrated abnormal behaviour of both carborane series (1A[n] and 1B[n]) and also the cyclohexane series (1D[n]). The former showed progressive destabilisation of the mesophase, whereas the series 1D[n] exhibited increasing mesophase stability relative to 1E[n] with increasing chain length. Both of these effects were explained using conformational analysis of theoretical models and experimental molecular structures for 1A[3], 1B[4] and 1C[4]. The increasing relative destabilisation of the mesophase in the carborane derivatives was rationalised by the high order rotational axes in A and B and D _4d symmetry for B. The trend of the ΔT _MI values for series 1D[n] was explained with the existence of the equatorial‐axial conformational equilibrium for the cyclohexane derivatives. The clearing temperatures for the hypothetical pure diequatorial conformers 1D[n]‐ee were estimated.     

Manifestations of the Alder-Rickert reaction in the structures of bicyclo[2.2.2]octadiene and bicyclo[2.2.2]octene derivatives

The Alder-Rickert ethylene extrusion reaction manifests in the ground state structures of compounds 9-12 which contain the bicyclo[2.2.2]octadiene moiety and compounds 13, 14, and 17-20 which contain the bicyclo[2.2.2]octene moiety. A significant decrease of the 13C-13C one-bond coupling constants for the C-C bonds, which break in this fragmentation reaction, suggests lengthening, and hence weakening of these bonds. In the unsymmetrical systems these effects are also shown to be associated with strengthening of the CH2-CH2 bond, which is ultimately lost from the molecule as ethylene. Low-temperature crystal structures of compounds 9-12 and 16 provide evidence for similar crystal packing requirements of the CH2-CH2 and CH=CH moieties.     

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.     

Thermal behaviour of some dibenzobicyclo[2.2.2]octane derivatives

A number of dibenzobicyclo[2.2.2]octane derivatives have been studied due to the interest of such compounds as ligands for coordination compounds with potential biological activity. Their thermal behaviour has been analyzed in order to find out more information about their fragmentation. A connection between the bridge substituents and the fragmentation process has been observed.     

Synthesis,characterization, and properties of colorless rigid-rod poly(benzobisthiazole) derived from bicyclo[2.2.2]octane

Polycondensation in polyphosphoric acid of 2,5-diamino-1,4-benzene dithiol dihydrochloride with bicyclo[2.2.2]octane-1,4-dicarboxylic acid, as well as the corresponding dimethyl ester or diacid chloride, led to rigid-rod benzobisthiazole polymers. Colorless and soluble polymers with intrinsic viscosities as high as 30.6 dL/g (methanesulfonic acid, 30°C) were obtained. The ultraviolet-visible spectrum of a polymer film cast from methanesulfonic acid under reduced pressure displayed no absorptions in the visible range (400–900 °m). The polymer was thermooxidatively stable up to 420°C in air as determined by thermogravimetric analysis. Fibers spun from a lyotropic polyphosphoric acid solution exhibited a tensile strength of 300–450 Ksi, a modulus of 26 Msi, and a compressive strength of 53 Ksi. Wide-angle X-ray scattering patterns of polymer fibers indicated a 3-dimensional crystal structure rather than a nematic liquid crystal structure. © 1994 John Wiley & Sons, Inc.     

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.     

Simple construction of bicyclo[4.3.0]nonane,bicyclo[3.3.0]octane,and related benzo derivatives by palladium-catalyzed cycloalkenylation

[reaction: see text] Bicyclo[4.3.0]nonanes (hydrindanes) and bicyclo[3.3.0]octanes (octahydropentalenes) are easily synthesized by palladium-catalyzed cycloalkenylations. Additionally, benzo-fused bicyclo[3.3.0]octanes are prepared for the first time through intramolecular coupling between silyl enol ethers and aromatic rings in the presence of catalytic palladium acetate.     

Synthesis and characterization of poly(benzazoles) containing the bicyclo[2.2.2]octane moiety

Poly(benzobisoxazoles) (PBOs), poly(benzobisthiazoles) (PBTs) and copolymers thereof containing the 2,5-dihydroxybicyclo[2.2.2]octane moiety have been prepared and studied. The homopolymers were synthesized by the polycondensation of 2,5-dihydroxybicyclo[2.2.2]octane-1,4-dicarboxylic acid with 4,6-diamino-1,3-benzenediol dihydrochloride or 2,5-diamino-1,4-benzenedithiol dihydrochloride in poly(phosphoric acid). Random and block copolymers (PBO–PBT) were also prepared. The polymers were characterized by solubility, X-ray diffraction, spectroscopy (infrared and solid-state ¹³C nuclear magnetic resonance), and thermal analysis such as differential scanning calorimetry and thermogravimetric analysis. Thermogravimetric analysis showed thermal stability of the polymers above 375°C in air and under argon atmosphere. The polymers exhibited high resistance to organic and inorganic solvents. The polymers were converted to the more stable aromatic polymers via dehydration and retro Diels–Alder reactions of the 2,5-dihydroxybicyclo[2.2.2]octyl moiety by pyrolysis. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 277–281, 1998