A bismethano-bridged bisdehydro[21]annulenone, tricyclo[15.4.1.16,11]tricosa-6,8,10,12,15,17,19,21-octaene-2,4-diyn-14-one, was synthesized. X-ray crystallography reveals the syn orientation of the two methano bridges. Two conformers are present in solution in a 97:3 ratio, the major isomer being the one existing in the crystalline state. Paratropicity of this compound in CDCl3 and in CF3CO2D is discussed.

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Synthesis and Properties of a Bismethano-Bridged Bisdehydro(21) annulenone. Conformation in Solution and in the Crystalline State. -The title-compound (IX) exists in two conformers in solution. The major isomer is the one existing in the solid state. -(HIGUCHI, H.; KIYOTO, S.; SAKON, C.; HIRAIWA, N.; ASANO, K.; OJIMA, J.; INOUE, K.; YA-MAMOTO, G.; Chem. Lett. (1994) 12, 2291-2294; Dep. Chem., Fac. Sci., Toyama Univ., Gofuku, Toyama 930, Japan; EN)

Synthesis and Properties of Dimethano-Bridged Tetradehydro(21)-, -(23)-and -(25)annulenones.-The synthesis of several annulenones, e.g. (IV), is described. 1H-NMR and electronic spectra are discussed in view of structure and tropicity of these compounds. -(OJIMA, J.; HIRAIWA, N.; KONDO, S.; ASANO, K.; SAKON, C.; HIGUCHI, H.; INOUE, K.; YAMAMOTO, G.; J. Chem. Soc., Perkin Trans. 1 (1995) 23, 3027-3036; Dep.