Synthesis of Substituted Tetralins and Benzosuberans via BF₃·OEt₂‑Mediated Formal (4 + 2) and (5 + 2) Stereocontrolled Cycloaddition of 4‑Alkenols with Veratrol

BF3·OEt2-mediated one-pot formal (4 + 2) and (5 + 2) stereocontrolled cycloaddition of 4-alkenols 3 and 4 with veratrol affords the respective substituted tetralins 5 and benzosuberans 6 in good yields. The cascade protocol combines a facile double Friedel–Crafts benzannulation of 4-alkenols 3 and 4 (having two electrophilic sites) and veratrol (7a) (having two nucleophilic sites). A plausible mechanism was studied and proposed.以三氟化硼乙醚络合物（BF3·OEt2）介导的一锅法形式[4+2]与[5+2]立体可控环加成反应，以4-烯醇类化合物3、4与藜芦醚（veratrol，7a）为底物，可分别以良好收率得到各自的取代四氢萘（tetralins）5与苯并环庚烷（benzosuberans）6。该级联反应策略结合了对具有两个亲电位点的4-烯醇类化合物3、4，以及具有两个亲核位点的藜芦醚（veratrol，7a）所进行的简便双重傅-克苯环化过程。本研究对该反应的合理反应机理进行了探究，并提出了相应的反应路径。