The Synthesis Of 2- Substituted Benzoxazoles And 2- Substituted Benzimidazoles

2-Substituted benzoxazoles and 2-substituted benzimidazoles are important class of heterocyclic compounds, much effort have been devoted to the development of synthetic methods for the synthesis of the 2-substituted benzoxazoles and 2-substituted benzimidazoles. The main work included in this dissertation is described in the following four parts:The first part:We have reviewed the recent studies about the synthesis of the 2-substituted benzoxazoles and 2-substituted benzimidazoles.The second part:Cs₂CO₃-catalyzed reaction of o-aminophenol, o-diaminobenzene and aromatic aldehyde affording 2-substituted benzoxazoles and 2-substituted benzimidazoles were investigated. The effects of catalysts, solvents and reaction temperature on yield of the product were examined,and 33 mmol% Cs2CO3, 0.12 g 4?MS can works efficiently for the reaction of o-aminophenol and o-diaminobenzene with aromatic aldehydes in DMF at 80℃ to yield a series of 2-substituted benzoxazoles in 52%-83% yield and 2-substituted benzimidazoles in 60%-83% yield,respectively. This protocol has advantages of mild condition and high yield, but low yields of some substrates and functional group tolerance were limited.The third part : The reaction of o-aminophenols, o-diaminobenzenes and aromatic aldehydes affording 2-substituted benzoxazoles and 2-substituted benzimidazoles via m-CPBA promoted oxidation was investigated. The effects of solvents and reaction temperature on yield of the product were examined, and 2equiv m-CPBA can works efficiently for the reaction of o-aminophenol and o-diaminobenzene with aromatic aldehydes in 1,2-DCE at 60 oC to yield a series of 2-substituted benzoxazoles in 56%-98% yield and 2-substituted benzimidazoles in 73%-88% yield,respectively. This protocol has advantages of mild condition and high yield, but moderate yields of some aldehydes with electron-donatingThe fourth part:Catalyst-free one-pot synthesis of 2-substituted benzoxazoles from o-aminophenol, 1,2-diaminoarenes and aromatic aldehydes was investigated. The effects of solvents and reaction temperature on yield of the product were examined, and a series of 2-substituted benzoxazoles were prepared in 64%-95% yield and 2-substituted benzimidazoles in 83%-94% yield was respectively. This protocol has advantages of high yield,but low yields of some substrates,such as salicylaldehyde.