Raison d'etre of apparently antiaromatic 1,2-dithiin derivatives in nature

Although living organisms tend to avoid synthesizing antiaromatic molecules because of their thermodynamic and kinetic instability, some composite plants synthesize apparently antiaromatic 1,2-dithiin derivatives. Molecular orbital calculations at the HF/6-31G** level revealed that the antiaromaticity of the 1,2-dithiin ring is markedly reduced by assuming a non-planar molecular structure. It was found that both 1,2- and 1,4-dithiin rings are essentially nonaromatic with the Dewar resonance energies being close to zero. This must be the primary reason why 1,2-dithiins occur in nature. (C) 1999 Elsevier Science B.V. All rights reserved.