Synthesis of unsymmetrical A3B type meso-tetraaryl triphyrin(2.1.1)s.

A series of unsymmetrical 1-(p-tolulyl)-5,6-di(p-tolyl)-10-(acyl)-dipyrroethenes were synthesized in two steps starting with 5,6-di(p-tolyl)dipyrroethene. In the first step, 5,6-di(p-tolyl)dipyrroethene was subjected to the Grignard reaction with 4-methylbenzoyl chloride to afford 1-(p-tolulyl)-5,6-di(p-tolyl)dipyrroethene, which was then subjected to another Grignard reaction with different aryl acid chlorides such as benzoyl chloride, 4-iodobenzoyl chloride, 4-methoxybenzoyl chloride, 2-thiophene carbonyl chloride and 2-furoyl chloride to afford unsymmetrical 1-(p-tolulyl)-5,6-di(p-tolyl)-10-(acyl)-dipyrroethenes in 67-75% yields. The unsymmetrical 1,10-diacyl-5,6-di(p-tolyl)dipyrroethenes were in situ reduced by NaBH4 to corresponding unsymmetrical diols and condensed with pyrrole under mild acid catalysed conditions followed by chromatographic purification to afford the first examples of A3B type meso-tetraaryl triphyrin(2.1.1)s in 16-19% yields. The unsymmetrical A3B type meso-tetraaryl triphyrin(2.1.1)s were thoroughly characterized and studied by HRMS, NMR, X-ray crystallography for one of the triphyrins, absorption and fluorescence spectroscopy, cyclic voltammetry and theoretical techniques. Furthermore, the utility of mono-functionalized A3B type meso-tetraaryl triphyrin(2.1.1) is demonstrated through the synthesis of a covalently linked ferrocene-triphyrin(2.1.1) dyad. The preliminary studies showed a possibility of photoinduced electron transfer from the ferrocene moiety to the triphyrin(2.1.1) macrocycle.