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.