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 beta-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 all unexpected decrease in planarity in the analogue with the triple bond as opposed to that with the double bond. (C) 2008 Elsevier Ltd. All rights reserved.