A simple route to prepare mono-functionalized 21-thia, 21,23-dithia and 21-thia-23-oxaporphyrins using unsymmetrical thiophene diols as key synthons and their use in the synthesis of of covalently linked unsymmetrical porphyrin dimers

Abstract

A series of unsymmetrical thiophene diols has been prepared in two steps from thiophene in 16–46 % yields. The unsymmetrical thiophene diols containing functionalised aryl groups were then used as key synthons for the synthesis of a series of monofunctionalised 21-thia (N₃S), 21,23-dithia (N₂S₂) and 21-thia-23-oxaporphyrins (N₂SO). Condensation of one equivalent of unsymmetrical diol with either two equivalents of aldehyde and three equivalents of pyrrole, one equivalent of symmetrical 16-thiatripyrrane or one equivalent of symmetrical 16-oxatripyrrane under standard porphyrin-forming conditions resulted in monofunctionalised 21-thia-, 21,23-dithia- or 21-thia-23-oxaporphyrins in decent yields. This unsymmetrical diol method is simple, versatile and gives an access for the first time to any desired monofunctionalised porphyrins with N₃ S, N₂S₂ and N₂SO porphyrin cores. The use of monofunctionalised N₃S, N₂S₂ and N₂SO porphyrins is further demonstrated by synthesising the first examples of three new covalently linked diarylethyne-bridged unsymmetrical dimers containing two different porphyrin cores such as N₂S₂-N₄, N₂S₂-N₃S and N₂S₂-N₂SO.