Synthesis and Properties of a Bismethano-bridged Bisdehydro[21]annulenone. Conformation in Solution and in the Crystalline State

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.