Mechanism of the thermal conversion of tetracyclo[3.3.0.02,4.0.3,6]oct-7-ene into dihydropentalenes

One of a number of possible mechanisms has been established for the title reaction.     

A synthetic entry into tetracyclo (4.2.0.02,4.03,8) octane system

Novel ceric ion oxidation of homocubanone provides a facile entry into tetracyclo(4.2.0.0^2,4.0^3,8)octane and tricyclo (3.3.0.0^2,7)octane ring systems.     

An INDO-LMO and 13C NMR spectroscopic study of the C-H bonds in tetracyclo[3.2.0.02,7.04,6]heptane (quadricyclane) and tricyclo[3.1.0.02,4]hexane

Using an INDO approximation to Von Niessen's charge density localization method, the percent s character of the C atom hybrid orbitals engaged in C-H bonds is computed for a series of open-chain and cyclic saturated and unsaturated hydrocarbons. A semi-empirical linear relationship is found between these quantities and the experimental nuclear spin-spin coupling constants J_CH (standard deviation 4·98 Hz). The experimental values of J_CH were measured for quadricyclane (1) and tricyclo[3.1.0.0^2,4]hexane (2) and were shown to be in fair agreement with the theoretical predictions. An analogous relationship is also established between the percent s character of the involved C atom hybrid orbital and the C-H bond distance, the standard deviation being 0·0040Å. This relation is used in order to predict the different C-H bond lengths in the vibrational ground state of 1 and 2, for which equal CH distances were assumed in the analysis of electron diffraction experiments. The results indicate that molecular geometries can be refined with the use of semi-empirical correlations of the above mentioned type.     

Synthesis of tetracyclo[3.3.0.02.4.03.6]oct-7-ene and some of its derivatives

A full account is given of the synthesis of the title compound, its 7,8-dihydro-analogue and of some of its derivatives.     

Charge-transfer absorption spectra between tetracyclo[3.2.0.02,7.04,6]heptane and π-type electron acceptors

Charge-transfer transition energies, association constants, and molar extinction coefficients of complexes between tetracyclo[3.2.0.0^2,7.0^4,6]heptane(quadricyclane) and olefine type or quinone type acceptors were measured in methylene chloride at 20°. An excellent linear relationship (r = 0·9938) with a slope of 0·96 was observed in plots of ν_max(CT) for a series of complexes of quadricyclane against ν_max(CT) for the corresponding complexes of N,N-dimethyl-aniline, indicating that quadricyclane forms electron donor-acceptor complexes of weak interactions. The first ionization potential, estimated from the hyperbolic relationship between the charge-transfer transition energy (E_CT) and the ionization potential, was an exceptionally low value (8·28–8·32 eV) for a saturated hydrocarbon and was indeed in the same order of magnitude with that of norbornadiene, which was well reproduced by EHM and MINDO/1 calculations applying Koopmans' theorem to the calculated HOMO energy.     

1,4,7,10-tetraazatetracyclo[5.5.1.04,13.010,13]tridecane: Degenerate rearrangement of its conjugate acid

The highly symmetrical 1,4,7,10-tetraazatetracyclo[5.5.1.0^4,13.0^10,13]tridecane (1) has been synthesized by two methods. The proton NMR spectrum of 1 is analyzed. The cyclic tetraaminomethane derivative undergoes a remarkable series of degenerate prototropic and conformational equilibria. The temperature dependence of the proton NMR spectra of 1 and its conjugate acid 3 are interpreted in terms of a large rate enhancement of intramolecular nucleophilic addition to guanidinium ion 3 (ring-chain tautomerism) compared to its acyclic counterpart.     

On the planarity of tetracyclo [5.5.1.04,13o10,13] tridecahexaene

MINDO/3 calculations indicate that tetracyclo [5.5.1.0^4,130^10,13] tridechexaene ($\text{1a}$) is nonplanar (D₂ symmetry) in its ground state with pronounced bond alternance.     

The synthesis and x-ray crystal structure of a tetracyclo[4.2.1.1.2,503,7]decane derivative. A rigid,twist boat-containing ring system.

Attempted intramolecular pinacolization of cage diketone $\text{4}$ unexpectedly gave ketol $\text{5}$ instead. Compound $\text{5}$ was shown to possess the rare tetracyclo[4.2.1.1.^2,50^3,7]decane ring system by means of an X-ray crystal structure of hydroxy-mesylate $\text{10}$ derived from $\text{5}$ by sodium borohydride reduction followed by mesylation. A possible mechanism for the transformation of $\text{4}$ into $\text{5}$ is presented, and certain noteworthy features of the crystal structure of $\text{10}$ are discussed. The base-catalysed fragmentation of $\text{10}$ to give enone $\text{11}$ is also described.