Merging [2+2] Cycloaddition with Radical 1,4‐Addition: Metal‐Free Access to Functionalized Cyclobuta[a]naphthalen‐4‐ols

• Published in: Angewandte Chemie International Edition Vol. 56; no. 49; pp. 15570 - 15574
• Main Authors: Liu, Feng, Wang, Jia‐Yin, Zhou, Peng, Li, Guigen, Hao, Wen‐Juan, Tu, Shu‐Jiang, Jiang, Bo
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 04-12-2017
• Edition: International ed. in English
• Subjects: Allene; allenes; annulation; Benzene; Cycloaddition; diazo compounds; Metals; radicals; Sulfur; Sulfur dioxide; YneS protein; allenes; annulation; cycloaddition; radicals; diazo compounds
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201707615

A metal‐free [2+2] cycloaddition and 1,4‐addition sequence induced by S‐centered radicals has been achieved by treating benzene‐linked allene‐ynes with aryldiazonium tetrafluoroborates and DABCO‐bis(sulfur dioxide) in a one‐pot procedure. The reaction provides a greener and more practical access to functionalized cyclobuta[a]naphthalen‐4‐ols with valuable applications. More than 50 examples are demonstrated with excellent diastereoselectivity and chemical yields. The reaction pathway is proposed to proceed by the following steps:[2+2] cycloaddition, insertion of SO2, 1,4‐addition, diazotization, and tautomerization.
Just a DAB: A new metal‐free [2+2] cycloaddition/S‐centered radical induced 1,4‐addition sequence of benzene‐linked allene‐ynes has been established by treatment with aryldiazonium tetrafluoroborates and DABCO‐bis(sulfur dioxide) under convenient reaction conditions, thus providing practical access to functionalized cyclobuta[a]naphthalen‐4‐ols of chemical and biomedical importance. DABCO=1,4‐diazabicyclo[2.2.2]octane.