Mild, Modular, and Convergent Synthesis of Helical Naphtho[2,1‑c]chromenes via a Multistep Cyclization/Aromatization Cascade Sequence

Tetracyclic 6H-naphtho­[2,1-c]­chromenes are expeditiously synthesized through a BF3·OEt2-mediated, three-step cascade reaction, creating new central pyran and aromatic rings. The cascade involves the addition of phenol-derived alkynyl substrates to BF3-activated aldehydes followed by alkyne-Prins cyclization, Friedel–Crafts reaction, and final elimination. Aliphatic and electron-deficient aromatic aldehydes afford the products in 50–74% isolated yields, but benzaldehyde and tolualdehyde resulted in lower yields. X-ray analysis of a p-bromophenyl derivative (5aA) shows the two aromatic moieties are twisted by 28° to create a helical backbone.四环6H-萘并[2,1-c]色烯（Tetracyclic 6H-naphtho[2,1-c]chromenes）可通过三氟化硼乙醚络合物（BF3·OEt2）介导的三步级联反应快速合成，同步构建出新的中心吡喃环与芳香环。该级联反应流程包括：将酚类衍生的炔基底物加成至经BF3活化的醛类底物中，随后依次发生炔烃-Prins环化、傅-克反应以及最终的消除步骤。脂肪族醛与缺电子芳香醛可获得50%~74%的分离收率，但苯甲醛和甲苯甲醛的反应收率相对更低。对溴苯基衍生物（5aA）的X射线衍射分析结果显示，其两个芳香基团以28°的夹角相互扭转，形成螺旋状分子骨架。