Dehydroannulenes. III. Synthesis and Properties of 1,5,10,14-Tetra-tert-butyl-6,8,15,17-tetrakisdehydro[18]annulene

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In order to find out substituent groups which provide stability and solubility to tetrakisdehydro[18]annulene system without appreciable electronic interaction with the annulene ring, the synthesis of 1,5,10,14-tetra-tert-butyl-6,8,15,17-tetrakisdehydro[18]annulene (VIII) has been catrried out starting from 3-tert-butyl-2-penten-4-ynal (III). It was found that the tetra-tert-butyl derivative (VIII) is strongly diatropic, and more stable and much more soluble than tetramethyl-, dimethyl-, diphenyl-, and tetraphenyl-analogues. The electronic spectrum of tetra-tert-butyl derivative (VIII) was found to be closely related with that of tetramethyltetrakisdehydro[18]annulene indicating a minor electronic perturbation of tert-butyl groups on the annulene ring.