Electrophilic Cyclization Involving Carbon–Selenium/Carbon–Halide Bond Formation: Synthesis of 3‑Substituted Selenophenes

The butylselanyl propargyl alcohols reacted with iodine to afford 3-iodoselenophenes. The change of nucleophile position from propargyl to homopropargyl was crucial for the aromatization and formation of selenophene rings. The experiments revealed that bromine and N-bromosuccinimide were not able to cyclize the butylselanyl propargyl alcohols; however, when the bromine source was copper­(II) bromide the corresponding 3-bromoselenophenes were obtained in good yields. In addition, the reaction of butylselanyl propargyl alcohols with diorganyl diselenides catalyzed by copper­(I) iodide gave the 3-(organoselanyl)­selenophenes. The reaction took place with aromatic rings substituted by either electron-donating or -withdrawing groups in the alkynes and propargyl positions. The steric effects of substituents were dominant in determining the yields, whereas electronic effects had only a minor influence. Furthermore, by monitoring the reaction by 1H NMR, we were able to identify the key intermediate, which supported the elaboration of a proposed reaction mechanism. The 3-iodoselenophenes prepared allowed the synthesis of multifunctional selenophenes via application in metal-catalyzed coupling reactions, such as Sonogashira, Ullmann and Suzuki type reactions.丁硒基炔丙基醇（butylselanyl propargyl alcohols）与碘反应可生成3-碘硒吩（3-iodoselenophenes）。将亲核位点从炔丙基调整至高炔丙基，对芳构化过程及硒吩环的形成至关重要。实验研究表明，溴与N-溴代丁二酰亚胺（N-bromosuccinimide）无法实现丁硒基炔丙基醇的环化转化；但当溴源为溴化铜(II)（copper(II) bromide）时，可获得收率优异的3-溴硒吩。此外，在碘化铜(I)（copper(I) iodide）催化下，丁硒基炔丙基醇与二有机二硒化物（diorganyl diselenides）发生反应，可生成3-(有机硒基)硒吩（3-(organoselanyl)selenophenes）。该反应适用于炔烃及炔丙基位带有给电子或吸电子取代基的芳香基底物。取代基的空间位阻效应是影响反应收率的主导因素，而电子效应的影响则相对微弱。此外，通过1H核磁共振谱（1H NMR）监测反应进程，我们成功鉴定出关键中间体，这为所提出的反应机理的构建提供了实验依据。所制备的3-碘硒吩可通过参与金属催化偶联反应（如Sonogashira、Ullmann及Suzuki型偶联反应），实现多功能硒吩的合成。