DOI: 10.1021/acs.orglett.6c03660 ISSN: 1523-7060
Ligand-Free Eu(OTf)3-Enabled Photoactivation for Strain-Release Photocycloadditions of Bicyclo[1.1.0]butanes with Substituted Alkenes
Qiujie Qin, Sicong Tu, Yunzhi Xie, Zijie Qin, Zixi Wang, Mingzhiyuan Bao, Xinchen Zhang, Yanjun Li, Zijun ZhouAbstract
Generating 1,3-diradicals from bicyclo[1.1.0]butanes typically requires precious-metal photocatalysts or sensitizers. We report that commercial, ligand-free Eu(OTf)3 coordinates N-phenylacylimidazole BCBs, enabling direct 420 nm absorption to access a BCB-derived diradical without external chromophores. This single platform enables strain-release [2σ+2π] and [2σ+3π] photocycloadditions with electron-poor and aryl alkenes and annulations with α-vinyl azides. Mechanistic studies, gram-scale synthesis, and a sonidegib bioisostere demonstrate broad utility for sp3-rich scaffold construction.