Investigation of photoreaction for 2-nitrobenzofuran and its 3-methyl derivative

• Photoreactions of 2-nitrobenzofuran and its 3-methyl derivative were investigated.
• Nitro–nitrite rearrangement selectively occurs in 2-nitrobenzofuran.
• Photoreaction of 3-methyl-2-nitrofuran underwent dimerization.

Aromatic nitro compounds undergo various photoreactions such as photosubstitution, photoredox reactions, photodissociation, and photoinduced nitro–nitrite rearrangements. The reaction mechanisms for these photoreactions, especially nitro–nitrite rearrangement reactions have never been completely understood. It was originally assumed that the potential cause for a nitro–nitrite rearrangement originates from the twisted dihedral angle between the plane of the nitro group and the plane of the aromatic ring [O.L. Chapman et al., J. Am. Chem. Soc. 88 (1966) 5550–5554]. Although the majority of aromatic nitro compounds have coplanar conformation and undergo nitro–nitrite rearrangement, no studies clearly substantiate this theory. This study reports on the photochemical reactions of 2-nitrobenzofuran and the effects of 3-methyl substituent on the compound. The results show that a nitro–nitrite rearrangement selectively occurs in deaerated acetonitrile solution for the photoreactions of 2-nitrobenzofuran. Moreover, nitro–nitrite rearrangement might occur in the photoreaction of 3-methyl-2-nitrobenzofuran. The quantum yield of degradation for 3-methyl-2-nitrobenzofuran was higher than that for 2-nitrobenzofuran, indicating that the methyl substituent at the 3-position changes the photoreactivity of 2-nitrobenzofuran.

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