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Due in part to their importance in nature, porphyrins have been synthetically investigated to determine their properties and potential applications. Azuliporphyrins 1, porphyrin analogues that possess a bicyclic azulene subunit, have intriguing properties that include the ability to form organometallic derivatives under mild conditions. In order to further investigate this unusual porphyrinoid system, the synthesis of methyl-substituted azuliporphyrin 1c and deazaazuliporphyrin 2 have been chosen as synthetic targets. 6-tert-Butyl- and 6-methylazulene, 3a and 3b, were reacted with two equivalents of an acetoxymethylpyrrole 4 in the presence of an acidic clay catalyst to give azulitripyrranes 5. Good yields were obtained for 5a but the methylsubstitute azulitripyrrane 5b was isolated in comparatively low yields. Although 5a reacts with pyrrole dialdehydes to give good yields of azuliporphyrins, this reaction failed for 5b, possibly due to the acidic nature of the methyl substituent. tert-Butylazulitripyrrane was also converted into the corresponding dialdehyde 6a by sequential treatment with trifluoroacetic acid and trimethyl orthoformate. Currently, the conversion of this species into a stretched dialdehyde 6b is under investigation. It is anticipated that McMurry condensation will convert 6b into deazaazuliporphyrin 2. This novel macrocycle will allow us to probe how the missing nitrogen atom affects the aromatic properties of these compounds.
Johnston, Rachel, "Investigation into the Synthesis of Porphyrin Analogues from Azulitripyrranes" (2020). Chemistry. 4.