Crown Ether‐Bearing Dihydroazulens[1]: Synthesis and Photochromism of a Benzo[15]crown‐5 Derivative

Photosensitive crown ether 1 composed of 1,8a-dihydroazulene as a photodynamic unit and a benzo[15]crown-5 ether subgroup has been synthesized from C-7-substituted cycloheptatriene 8, which has been obtained by nucleophilic addition of 4-acetylbenzo[15]crown-5 (6) to tropenylium tetrafluoroborate (7). Dehydrogenation of dicyanovinyl derivative 9 leads to heptafulvene 2 which thermally rearranges to dihydroazulene 1. Attempts to synthesize 1 according to the „[8 + 2]-cycloaddition route” have been unsuccessful. Crown ether 1 shows photochromic bistability with a photochemically driven forward and a thermal back reaction. The spectroscopic properties of 1 and the photochemical isomerization 1 2 have been shown to be almost insensitive to sodium iodide addition. The rate of the thermal back reaction 2 1 slightly is affected by sodium iodide addition.

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