Study On Lewis Acid Catalyzed Syntheses Of Benzocycloether Compounds

The Lewis acid catalyzed syntheses of benzocycloether and benzoxazole compounds were studied in this thesis, which is divided into three parts:1. An efficient and atom-economical method for the synthesis of benzopyrans by aluminium chloride catalyzed reaction of phenols with conjugated dienes was developed. Moreover, a selective reaction of phenols with 2,3-dimethyl-1,3-butadiene catalyzed by aluminium chloride under mild conditions was also developed. Benzopyrans were obtained in high yields at higher temperature, whereas lower temperature afforded benzofurans in high yields. A mechanism involving an aluminium chloride-catalyzed tandem Friedel-Crafts/hydroalkoxylation was proposed and the in situ formed aluminum phenoxide was the real active species of the reaction.2. A highly efficient method for the synthesis of benzopyrans by zinc chloride catalyzed reaction of phenols with prenyl bromide was developed, which provides a practical process to afford benzopyrans in good yields using commercially available and inexpensive catalyst under mild conditions. The possible mechanism of the reaction was proposed.3. Cationic lanthanide complex [Yb（CH₃CN）₉]³⁺[（AlCl₄）₃]^3–·CH₃CN was explored as a catalyst for the coupling reaction of 2-（benzylideneamino）phenol to yield benzoxazole. Reaction conditions were investigated and benzoxazole was obtained in moderate yield.