Ambient temperature synthesis of β,β'-fused nickel(II) pyrrolo[1,2-a]pyrazinoporphyrins via a DBSA-catalyzed Pictet-Spengler approach.

A facile first synthetic strategy to construct novel π-extended β,β'-fused nickel(II) pyrrolo[1,2-a]pyrazinoporphyrins has been developed via a Pictet-Spengler reaction of newly prepared nickel(II) 2-amino-3-(pyrrol-1-yl)-5,10,15,20-tetraphenylporphyrin with various aromatic, aliphatic or heterocyclic aldehydes in the presence of 10 mol% p-dodecylbenzenesulfonic acid (DBSA) as an efficient Brønsted acid catalyst in 1,4-dioxane at 25 °C. A variety of these π-extended porphyrin analogues were obtained in moderate to good yields under mild conditions and characterized on the basis of spectral data and single crystal X-ray analysis.