Stabilization of [2.2]paracyclophane anion as a result of transannular interaction

The review surveys methods for the construction of bi- and polycyclic nitrogen-, oxygen-, and sulfur-containing heterocycles based on reactions of 2-halobenzoyl chlorides with dinucleophiles.     

Functionalization and kinetic stabilization of the [4]paracyclophane system and aromaticity of its extremely bent benzene ring

Kinetic stabilization of the [4]paracyclophane skeleton by the introduction of substituents, which serve to sterically hinder reactions at the reactive bridgehead sites, and properties of the resultant [4]paracyclophanes are investigated in this study. Modification of the property of [4]paracyclophane by functionalization is also intended. [4]Paracyclophanes are designed to be derived from the corresponding Dewar benzene isomers via their photochemical aromatization, and the requisite 1,4-bridged Dewar benzenes bearing sterically demanding functional groups are prepared. Irradiation of these precursors under matrix isolation at 77 K leads to the formation of [4]paracyclophanes, which exhibit characteristic electronic absorption spectra. The half-lives of the generated species vary widely from less than 1 min at -90 degrees C to 0.5 h at -20 degrees C, depending on the type of substituents and the pattern of substitution. One of the derivatives, 24, is stable enough and its content in the irradiated mixture is high enough to permit the measurement of the (1)H NMR spectrum. The recorded spectrum, which is reproduced very well by theoretical calculations using the GIAO method at the hybrid HF-DFT (B3LYP/6-31+G*) level, suggests the sustenance of rather strong diatropicity in its severely bent benzene moiety. Calculations on the bent benzene whose geometry is constrained to that calculated for 24 support that aromaticity is retained to a significant extent as compared to that of planar benzene, as judged by the magnetic criteria of aromaticity, that is, diamagnetic susceptibility exaltation and nucleus-independent chemical shift. The reason for the retention of aromaticity despite the severe bending of the benzene ring is discussed. Cyclophane 24 is so strained that it exceeds the corresponding Dewar benzene precursor in energy and thermally reverts to the latter with a half-life of 15 +/- 5 min at -20 degrees C (DeltaG++ = 18.3 +/- 0.3 kcal mol(-1)).     

A new approach to the [6]paracyclophane system: synthesis of 2,3-dicarbethoxy[6]paracyclophane

The reaction of the dibromide $\text{1}$ with McMurry's reagent gives 2,3-dicarbethoxy[6]paracyclophane ($\text{2}$) in about 40% yield.     

X-ray crystal structure of a p-hydroxycalix[6]arene derivative

The first molecular structure of a p-hydroxycalix[6]arene 6 has been determined by a single crystal X-ray diffraction study. The calix[6]arene molecule assumes a 1,2,3-alternate conformation with all OH groups at the upper rim engaged in H-bonds with pyridine molecules. The stacking of molecules of p-hydroxycalix[6]arene 6 along the a and c axes gives rise to a solvent pseudo-cylindrical cavity at the centre of the cell.     

Photoreaction of a 2,11-diaza[3.3]paracyclophane derivative: formation of octahedrane by photochemical dimerization of benzene

Upon photoirradiation at 300 nm, the title diazaparacyclophane (R = COCF3) provided an octahedrane by the photodimerization of its benzene chromophores. This is the first photochemical formation of octahedrane, namely, via the dimerization of benzene. No octahedrane formation was observed for the photolysis of corresponding carbon-bridged paracyclophane. Thus the nitrogen bridges play an important role in the excited state to afford the octahedrane.     

Fullerene-acene chemistry: single-crystal X-ray structures for a [60]fullerene-pentacene monoadduct and a cis-bis[60]fullerene adduct of 6,13-diphenylpentacene

[structure: see text]. Crystal structures of the cis-bis[60]fullerene adduct of 6,13-diphenylpentacene (with the closest carbon atoms on adjacent fullerenes only 3.065(8) angstroms apart) and the [60]fullerene-pentacene monoadduct are in remarkably close agreement with the MM2 calculated structures.     

The first synthesis and characterization of both diastereomers of a di[2.2]paracyclophane: 4,4'-bis(1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane)

The synthesis and characterization of both diastereomers of a system comprised of two [2.2]paracyclophane units linked through a single 4,4' bond are described. Both the meso and d,l diastereomers of 4,4'-bis(octafluoro[2.2]paracyclophane) have been prepared via a palladium-catalyzed reductive homocoupling reaction by copper, producing a 3:2 ratio of meso and d,l diastereomers. A similar reductive homocoupling of pseudo-o-iodotrifluoromethyloctafluoro[2.2]paracyclophane gave only the analogous meso diastereomer. Single-crystal X-ray structures were obtained for all of the diparacyclophane products.     

Synthesis ofo-andm-carborane derivatives of [2,2]paracyclophane and abnormal Clemmensen reduction of ketones of the [2,2]paracyclophane and carborane series

Methods for the synthesis of [2,2]paracyclophane derivatives containingo- andm-carboranyl substituents in position 4, separated from the [2,2]paracyclophane system by one or two C atoms (alcohols and ketones) were developed. The Clemmensen reduction of a number of ketones of the [2,2]paracyclophane ando-carbonane series occurs abnormally. The reduction of 1-benzoyl-o-carboranes to the corresponding alcohols by zinc in ethanol in a neutral medium was performed for the first time. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1206–1211, June, 1997.     

Synthesis of a novel silicon-bridged [2.2]metacyclophan-9-ene and its photolytic transannular reaction

A novel [2.2]metacyclophane in which two benzene rings are linked together with a carbon-carbon double bond and a disilane unit was prepared. Photolysis of the cyclophane in the presence of oxygen afforded the 4,5-dihydro-4,5-disilapyrene derivative via a transannular dehydrogenation reaction.     

Synthesis and X-ray structure of a new pyrrolo[1,2-b]-pyridazine derivative

The synthesis, characterization and X-ray crystal structure of 2-(4-chloro-phenyl)-7-methylpyrrolo[1,2-b]pyridazine are reported. The compound crystallizes in the space group P2(1)/c (No.14) with a =3.8568(1), b = 11.0690(3), c = 26.4243(7) A, beta =92.777(1) degrees and Z = 4. Accurate molecular parameters for the novel heterocyclic system were obtained from intensity data collected at 113K. The molecule assumes a planar conformation in the crystal and the packing is based on pi-pi stacking with interplanar spacing 3.400 ?, typical of aromatic molecules with potential for displaying useful optical properties.     

X-ray structural investigation of a derivative of the alkaloid kesselringine

The molecular and crystal structures of 2,6-dimethyl-12-demethylkesselringine methosulfate have been determined by x-ray structural analysis. The relative configurations of the chiral centers in the R, S nomenclature have been established.Institute of Bioorganic Chemistry, Academy of Sciences of the Uzbek SSR, Tashkent; V. I. Lenin State University, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 89–92, January–February, 1986.     

Two-photon absorption of [2.2]paracyclophane derivatives in solution: a theoretical investigation

The two-photon absorption of a class of [2.2]paracyclophane derivatives has been studied using quadratic response and density functional theories. For the molecules investigated, several effects influencing the two-photon absorption spectra have been investigated, such as side-chain elongation, hydrogen bonding, the use of ionic species, and solvent effects, the latter described by the polarizable continuum model. The calculations have been carried out using a recent parallel implementation of the polarizable continuum model in the DALTON code. Special attention is given to those aspects that could explain the large solvent effect on the two-photon absorption cross sections observed experimentally for this class of compounds.     

Synthesis of 1,1,9,9-tetrafluoro[2.2]paracyclophane and its polymerization by vapor deposition method

1,1,9,9-Tetrafluoro[2.2]paracyclophane ( 1 ) was prepared successfully as white crystals in 72% yield via two-step reactions from 1,9-diketo[2.2]-paracyclophane. The polymerization of 1 by the vapor deposition method was carried out at pyrolysis temperature range of 400 to 800°C and deposition temperature range of ?20 to 20°C, and a tough, transparent poly(α,α-difluoro-p-xylylene) film was obtained in 72% yield at the pyrolysis temperature of 750°C and the deposition temperature of ?20°C. It was found that the pyrolysis of 1 gave a reactive α,α-difluoro-p-xylylene, which polymerized on the head-to-tail addition to give poly(α,α-difluoro-p-xylylene). Some properties such as solubility, thermal stability, glass transition temperature, and density for poly(α,α-difluoro-p-xylylene) were studied. © 1995 John Wiley & Sons, Inc.     

Production,isolation and structural characterization of [92]fullerene isomers

High-resolution 13C NMR has been used to structurally characterize a single isomer possessing C2 molecular symmetry as well as an inseparable mixture of other isomers of [92]fullerene, produced from dysprosium arc-burned soot, separated and isolated via multi-stage recycling HPLC.     

Structurally diverse second-generation [2.2]paracyclophane ketimines with planar and central chirality: syntheses, structural determination, and evaluation for asymmetric catalysis

A set of 20 novel [2.2]paracyclophane ketimines with planar and central chirality has been synthesized from enantiomerically pure and racemic 5-acyl-4-hydroxy[2.2]paracyclophane and alpha-branched chiral amines. Their X-ray structures were determined to elucidate the three-dimensional structures and the absolute configuration. The ketimines were used as catalysts in the asymmetric 1,2-addition reactions of diethylzinc with substituted benzaldehydes to furnish chiral alcohols in up to 95 % ee.     

Aromaticity of strongly bent benzene rings: persistence of a diatropic ring current and its shielding cone in [5]paracyclophane

Direct evaluation of the induced π current density in [5]paracyclophane (1) shows that, despite the significant non-planarity (α = 23.2°) enforced by the pentamethylene bridge, there is only a modest (ca. 17%) reduction in the π ring current, justifying the use of shielding-cone arguments for the assignment of (1)H NMR chemical shifts of 1 and the claim that the non-planar benzene ring in 1 retains its aromaticity (on the magnetic criterion).