meso,β‐Oligohaloporphyrins as Useful Synthetic Intermediates of Diphenylamine‐Fused Porphyrin and meso‐to‐meso β‐to‐β Doubly Butadiyne‐Bridged Diporphyrin

The chlorination of β‐halo or β,β‐dihaloporphyrins with 2‐chloro‐1,3‐bis(methoxycarbonyl)guanidine (Palau′Chlor) proceeded selectively at the neighboring unsubstituted meso position to afford meso,β‐dihalo or meso,β,β‐trihaloporphyrins. Such oligohaloporphyrins are useful platforms for constructing more‐elaborate porphyrin‐based extended π systems. For example, meso‐chloro‐β,β‐diiodoporphyrin participated in an efficient single‐step synthesis of a diphenylamine‐fused porphyrin. In addition, meso‐chloro‐β‐iodoporphyrin was transformed in stepwise fashion into an efficiently conjugated meso‐to‐meso,β‐to‐β doubly butadiyne‐linked porphyrin dimer, a system which was previously difficult to access without such haloporphyrin precursors.