Synthesis of 2-Aryl-2H-indazoles by TiO_2-Photocatalyzed Reaction of Alkoxyazobenzenes

摘要

3-Substituted 5-alkoxy-2-aryl-2H-indazoles were synthesized in low to moderate yields by the TiO_2-photocalyzed reaction (#lambda# > 280 nm) of 4-alkoxyazobenzenes in alcohols. The formation of hydroxyalkyl radicals and the presence of an electron-donating alkoxy groups in the starting azobenzenes are very important ini this reaction. This is an unique method for the synthesis of 3-substituted 5-alkoxy-2-aryl-2H-indazoles from 4-aloxyazobenzenes.