Synthesis of Polycyclic Heteroaromatic Coumarins via Photoinduced Dehydrogenative Annulation of 4‑Phenyl-3-heteroarylcoumarins

An efficient, oxidant and metal-free synthesis of polycyclic heteroaromatic coumarins was developed. H-Furo­[2′,3′:3,4]­naphtho­[2,1-c]­chromen-4-one (2a–2f), 1H-benzo­furo­[2′,3′:3,4]­naphtho­[2,1-c]­chromen-1-one (2g–2j), and 4H-thieno­[2′,3′:3,4]­naphtho­[2,1-c]­chromen-4-one (2k–2s) derivatives were obtained by the irradiation of 4-phenyl-3-hetero­aryl­coumarin in EtOH–H2O (9:1, v/v) using a high-pressure Hg lamp as the light source, at room temperature and under an Ar atmosphere. Owing to the expansion of the π-conjugation system, 2a–2s showed strong fluorescence emissions in ethanol solution (ΦF = 0.40–0.83).本研究开发了一种高效、无需氧化剂且无金属参与的多环杂芳基香豆素合成方法。H-呋喃并[2′,3′:3,4]萘并[2,1-c]色烯-4-酮（H-Furo[2′,3′:3,4]naphtho[2,1-c]chromen-4-one，2a–2f）、1H-苯并呋喃并[2′,3′:3,4]萘并[2,1-c]色烯-1-酮（1H-benzo[furo[2′,3′:3,4]naphtho[2,1-c]chromen-1-one，2g–2j）以及4H-噻吩并[2′,3′:3,4]萘并[2,1-c]色烯-4-酮（4H-thieno[2′,3′:3,4]naphtho[2,1-c]chromen-4-one，2k–2s）三类衍生物，可通过以4-苯基-3-杂芳基香豆素为底物，在体积比为9:1的乙醇-水（EtOH–H₂O，v/v）混合溶剂中，以高压汞灯为光源，于室温及氩气（Ar）氛围下进行光照反应制得。由于π共轭体系的拓展，2a–2s在乙醇溶液中展现出较强的荧光发射性能，其荧光量子产率（ΦF）为0.40~0.83。