W. H. De Wolf

Studies on the formation of [5]metacyclophane

Abstract Base induced elimination of HCl from the dichloro[5.3.1]propellane 3a gives a mixture of [5]metacyclophane ( 1 ) and tetrahydrocyclopentacyclooctenes ( 2 ), while the stereoisomeric 3b affords 1 quantitatively.

7,8-dimethoxycarbonyl-10,11-dimethyl[5]paracyclophane

Abstract The title compound ( 1 ) was obtained in 13% yield by UV irradiation of the corresponding Dewar benzene ( 2 ); it is considerably more stable than [5]paracyclophane itself.

8,11-dichloro[5]metacyclophane

Abstract The title compound 1b was prepared by treating the tetrachloroprellane 2 with AgClO 4 /2,6-lutidine in THF. Towards proton and dienophiles, 1b is less reactive than the unsubstituted 1a.

Scope and limitations of the flash vacuum thermolysis approach to small [n]paracyclophanes

Abstract Flash vacuum thermolysis (FVT) of 3-methylene-6-spirocyclohexa-1,4-dienes (2) was investigated as a synthetic approach to small [n]paracyclophanes 1 (1a, n = 8; 1b, n = 7; 1c, n = 6). The method was found to be preparatively attractive for 1a (80% yield), less so for 1b (7% useful yield), and not at all for 1c which was too unstable to survive the conditions of its formation. Besides 1, p-alkylstyrenes (3) and 2-methylbenzocycloalkenes (4) were obtained; the total recovery of monomeric products was good (60–85%). The temperature dependence of the product formation furnished useful information on the mechanisms of formation and decomposition of 1 under the conditions of FVT.

[5]metacyclophanes a spectroscopic and theoretical investigation of structure and conformation

Abstract The 1 H NMR spectra of [5]metacyclophane (1a) and of its 8,11-dichloro derivative 1b are reported. 1a Has a rigid conformation A between -50 and +150 °C. Conformation A is also the preferred one (85%) for 1b at -47 °C, but 1b-A is in equilibrium with a second conformer 1b-B, for which spectral parameters can be derived. A and B correspond with two energy minima predicted by MNDO calculations.

9-Hydroxy [7]metacyclophane

Abstract A new pyrolytic access to a metacyclophane has been found by the flash vacuum thermolysis of spiro[5,7]trideca-l,4-dien-3-one ( 4 ) which gave 9-hydroxy[7]metacyclophane (7) , and 4-(6-heptenyl)phenol (8) . The mechanism of formation of 7 and 8 from the intermediate diradical ( 6 ) is discussed.

Photochemical synthesis of arenetricarbonylchromium(0) complexes: scope and limitations

Abstract Two photochemical methods for the preparation of arenetricarbonylchromium(0) complexes are described. The first involves irradiation of a solution of hexacarbonylchromium(0) and arene in THF at room temperature with a medium pressure mercury lamp. In the second a suspension of hexacarbonylchromium(0) in THF is irradiated in the same way and the arene then added. The yields are generally lower than those obtained by the usual thermal methods, but there is advantage in the milder reactions conditions.

Chiroptical properties of 12,15-dichloro[3.0]orthometacyclophane - correlations between molecular structure and circular dichroism spectra of a biphenylophane

Abstract The valence excited electronic states and the circular dichroism (CD) spectra of the recently synthesized 12,15-dichloro[3.0]orthometacyclophane 1 are discussed by means of quantum chemical calculations which combine density functional theory with the single-excitation configuration interaction approach (DFT/SCI). The X-ray structure of this highly strained biphenylophane is presented. In order to investigate the influence of the cyclophane-type distortions on the CD spectrum of 1, the CD spectra of three model geometries (2a–2c) are also calculated. It appears that the CD spectrum of the biphenylophane 1 differs substantially from that of the corresponding unstrained biphenyl 2c. Furthermore, it is found that the pyramidalization of the bridging atoms of the cyclophane ring is an important factor for the red shift of the first band with respect to that of an unstrained benzene chromophore.

Note on the solvent dependence of the 1H-NMR coordination chemical shifts of tricarbonyl(η6-[8]paracyclophane) chromium. A caveat concerning its interpretation☆

The solvent dependence of the 1H-NMR coordination chemical shifts of tri-carbonyl(η6-[8]paracyclophane)chromium (1) may act as an obstacle to their use as a probe in assessing the quenching of the aromatic ring current due to η6-complexation.

Synthesis and valence isomerizations of 1,1′-tetramethylenebicyclopropenyl

Aus 1,2-Dimethylen-cyclohexan (I) erhalt man durch Addition von Dibromcarben, Reduktion mit Tributylstannan und Behandlung mit tert.-Butylat das Bis-spiro-dien (II), das bei -20°C mit Silberperchlorat zu Dewarbenzol-Derivaten (III) und (IV) umgelagert wird, wobei die Mengen von den Reaktionsbedingungen abhangen.