An alternative synthesis of β-pyrrolic acetylene-substituted porphyrins

A modified Horner–Emmons condensation reaction has been employed in the synthesis of acetylene-substituted porphyrins at the β-pyrrolic position. This technique was shown to have many advantages over the typically employed Sonogashira coupling method, including negating the requirement for a brominated porphyrin starting material. The electronic spectra of 2-(4′-carboxyphenyl)ethynyl-5,10,15,20-tetraphenylporphyrinato zinc(II) showed a red shift compared to the double bond equivalent, 4-(trans-2′-(2″-(5″,10″,15″,20″-tetraphenylporphyrinato zinc(II)yl))ethen-1′-yl)-1-benzoic acid. Comparison of the X-ray structures of 2-((4′-formyl)phenyl)ethynyl-5,10,15,20-tetraphenylporphyrinato zinc(II) and its analogue 4-(trans-2′-(2″-(5″,10″,15″,20″-tetraphenylporphyrinato copper(II)yl))ethen-1′-yl)-1-benzaldehyde showed an unexpected decrease in planarity in the analogue with the triple bond as opposed to that with the double bond.

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