Ring-opening of 5,15-dioxaporphyrin into 1,9-diaryldipyrrin by a reaction with Grignard reagents

A ring-opening of nickel 10,20-dimesityl-5,15-dioxaporphyrin (NiDOP) proceeded in a reaction with aryl Grignard reagents to afford 1,9-diaryldipyrrins instead of demetallation reaction to form a free base form. A reagent scope for the ring-opening reaction revealed that reactions with less-sterically hindered aryl Grignard reagents, such as phenyl and para-substituted phenylmagnesium bromides, provided the dipyrrin products. In contrast, no reaction occurred, and unreacted NiDOP was recovered when alkyl, ethynyl, and 2-thienylmagnesium bromides and sterically hindered mesitylmagnesium bromide were used for the reactions. Herein, the unique ring-opening reactivity of NiDOP and characterization of the 1,9-diaryldipyrrin products are reported.

Automated summary

A ring-opening reaction of nickel 10,20-dimesityl-5,15-dioxaporphyrin (NiDOP) with aryl Grignard reagents resulted in the formation of 1,9-diaryldipyrrins instead of the expected demetallation reaction. Reactions with less-sterically hindered aryl Grignard reagents yielded the dipyrrin products, while no reaction occurred with alkyl, ethynyl, and 2-thienylmagnesium bromides as well as sterically hindered mesitylmagnesium bromide. The unique ring-opening reactivity of NiDOP and the characterization of the 1,9-diaryldipyrrin products are reported.