Insertion−Coupling−Cycloisomerization Domino Synthesis and Cation-Induced Halochromic Fluorescence of 2,4-Diarylpyrano[2,3-<i>b</i>]indoles

2,4-Diarylpyrano[2,3-b]indoles are formed via a Pd−Cu-catalyzed insertion−coupling−cycloisomerization domino reaction in moderate yields. Although the tricyclic systems are nonfluorescent in solution, protonation, quaternation, or complexation with metal ions induces intense green luminescence. Most strikingly, selective halochromic fluorescence of zinc and magnesium over calcium ions classify the title compounds as metal-selective luminescence sensors.2,4-二芳基吡喃并[2,3-b]吲哚（2,4-Diarylpyrano[2,3-b]indoles）可通过钯-铜共催化的插入-偶联-环异构化串联反应制备，收率处于中等水平。尽管该类三环体系在纯溶液中不具有荧光特性，质子化、季铵化或与金属离子络合均可诱导其产生强烈的绿色发光。最引人注目的是，相较于钙离子，该类标题化合物对锌离子与镁离子展现出选择性的荧光变色响应（halochromic fluorescence），因此可被归类为具备金属离子选择性的发光传感器。