Retro-Diels-Alder approach to the synthesis of π-expanded azuliporphyrins and their porphyrinoid aromaticity

摘要

Bicyclo2.2.2octadiene (BCOD) fused azuliporphyrins were synthesized by 3+1 porphyrin synthesis of azulitripyrranes with diformylpyrroles. Subsequent retro-Diels-Alder reaction of the BCOD-fused azuliporphyrins afforded azulibenzo-, azulidibenzo-, and azulitribenzoporphyrins 1-5. NMR and UV/Vis spectra, as well as nucleus-independent chemical shift (NICS) calculations revealed that 1-5 and their diprotonated dications exhibit relatively low porphyrinoid aromaticity, which was dependent on the position and number of fused benzene rings present. Porphyrins: A series of azulibenzoporphyrins were synthesized based on 3+1 porphyrin synthesis and retro-Diels-Alder reaction of bicyclo2.2.2octadiene-fused precursors (see scheme). UV/Vis spectra and NICS calculations revealed that their diprotonated dications exhibited a low porphyrinoid aromaticity from the porphyrinlike π circuit, which was dependent on the position and number of fused benzene rings.