Synthesis of meso-Alkyl-Substituted Norcorrole-Ni Complexes and Conversion to 5-Oxaporphyrins(2.0.1.0).

The synthesis of antiaromatic Ni -norcorroles having primary, secondary, and tertiary alkyl groups at the reactive meso-positions was attempted. Reductive coupling of a Ni -dipyrrin precursor provided Ni -meso-dihexylnorcorrole, which underwent substantial degradation on silica gel. Introduction of tert-butyl groups was unsuccessful due to the difficult preparation of the corresponding dipyrrin precursor. Meanwhile, Ni -norcorroles with isopropyl and cyclohexyl groups were isolated as stable molecules under ambient conditions. Furthermore, we found that oxidation of Ni -meso-dialkylnorcorroles with hydrogen peroxide in the presence of sodium carbonate gave Ni -5-oxaporphyrins(2.0.1.0). In contrast, oxidation of Ni -meso-dimesitylnorcorrole under the same reaction conditions gave 10-oxaporphyrin(1.1.1.0). The contrasting reactivity can be attributed to the steric congestion around the meso-positions.