The facile isomerization of benzo[8,9]bicyclo[5.2.0]nona-2,4,8-triene to benzo[7,8]bicyclo[4.2.1]nona-2,4,7-triene promoted by L3M(CO)3 complexes (M = Cr,Mo, W). The crystal structure of the tricarbonyl complex of benzo[7,8]bicyclo[4.2.1]nona-2,4,7-triene

Benzo[8,9]bicyclo[5.2.0]nona-2,4,8-triene (I) isomerizes to benzo[7,8]bicyclo[4.2.1]nona-2,4,7-triene (II) in the presence of L₃M(CO)₃ complexes (L = CO, NH₃, CH₃CN; M = Cr, Mo, W). In THF at 40°C with (CH₃CN)₃CrCO₃ the uncomplexed II is formed together with smaller amounts of the corresponding η⁶-tricarbonylchromium complex, TCC-II. In n-butyl ether at 120°C with (NH₃)₃Cr(CO)₃ the main product is the latter complex. The structure of TCC-II has been determined by NMR and X-ray analysis.     

ESR spectrum of the radical anion of bicyclo[3.2.2]nona-3,6,8-triene-2-one

The radical anion of bicyclo[3.2.2]nona-3,6,8-triene-2-one has been characterised by ESR spectroscopy.     

Near Cancellation of Through Space and Through Bond Interaction in bicyclo[3.2.2]nona-6,8-diene

The photoelectron spectra of bicyclo[3.2.2]nonane and its five dehydrogenated analogues are reported. Analysis of the π-bands reveals that the unsymmetrical diene 5 retains the ‘natural order’ of the π-orbitals present in the lower homologues, i. e. the in-phase below the out-of-phase combination of the basis π-orbitals π_a and π_c. The isomeric diene 4 is the first member of the symmetrical homologous series (I), which inverts this order, so that a ₁(π) (in phase!) lies above b ₂(π) (out-of-phase!).     

Synthesis of Si- and N-containing bicyclo[4.2.1]nona-2,4-dienes and bicyclo[4.2.1]nona-2,4,7-trienes

A [6π+2π] cycloaddition of Si- and N-containing alkynes and 1,2-dienes to cyclohepta-1,3,5-trienes in the presence of the two-component catalytic system (acac)₂TiCl₂-Et₂AlCl gives rise to the corresponding bicyclo[4.2.1]nona-2,4-diene and bicyclo[4.2.1]nona-2,4,7-triene derivatives.     

The dominant role of hyperconjugation in the 9-oxabicyclo[4.2.1] nona-2,4,7-triene series

The synthesis and photodimerization of 9-oxabicyclo[4.2.1]nona-2,4,7-triene are described. The electronic structure of 9-oxabicyclo[4.2.1]nona-2,4,7-triene and variously saturated derivatives thereof was examined by means of UV photoelectron spectroscopy and calculation. The combined results give no indication of specific through-space lone-pair/τ or τ/τ interaction between the various appendages but offer clear sign of hyperconjugative coupling.     

Thionin oxide as a Possible Intermediate on Periodate Oxidation of 9-Thiabicyclo[6.1.0]nona-2,4,6-triene

9-Thiabicyclo[6.1.0]nona-2,4,6-triene was oxidized at ?15 to ?20°C with sodium periodate in a methanol-water medium. The major isolated product was established as $\text{cis}$3a,7a-dihydrobenzo[b]thiophene-$\text{cis}$-1-oxide, which is best explained as arising from intramolecular cycloaddition of a thionin oxide intermediate.     

Thermal [2+2] cycloaddition of allenynes: easy construction of bicyclo[6.2.0]deca-1,8-dienes, bicyclo[5.2.0]nona-1,7-dienes, and bicyclo[4.2.0]octa-1,6-dienes

The simple refluxing of allenynes, having a phenylsulfonyl functionality on the allenyl group, in xylene (or mesitylene) without microwave irradiation resulted in the efficient formation of bicyclo[5.2.0]nona-1,7-dienes and bicyclo[4.2.0]octa-1,6-dienes in high yields. This method was shown to be successfully applicable to the first construction of bicyclo[6.2.0]deca-1,8-dienes. Construction of the corresponding oxa- and azabicyclo[m.2.0] frameworks could also be attained. This thermal ring-closing reaction involves the formal [2+2] cycloaddition in which the distal double bond of an allenyl moiety exclusively served as one of the pi-components regardless of the position of the phenysulfonyl functionality on the allenyl moiety.