Metal‐Free Synthesis of Thermally Stable Fluorescent p‐Terphenyls by Ring Transformation of 2H‐Pyran‐2‐ones

Abstract

AbstractA metal‐free approach for the synthesis of p‐terphenyls 7 a–i and cyclic p‐terphenyls 9 a–d and 11 a–d is described via carbanion induced ring transformation reaction of 6‐biphenyl‐2H‐pyran‐2‐ones 5 with malononitrile 6, cyclohexanone 8 and 1,4‐cyclohexanedione monoethylene ketal 10 respectively. Additionally, the base‐mediated ring transformation reactions were working smoothly under mild reaction conditions and ring transformation products 7, 9 and 11 were isolated in good to excellent yields. The synthetic approach provides the flexibility of introducing of both electron‐withdrawing and ‐donating functionalities in p‐terphenyl architecture. Moreover, the photo physical properties of compounds 7, 9 and 11 were analyzed using UV‐visible and Fluorescence Spectroscopy. p‐Terphenyls 7 c showed cyan fluorescence in chloroform (λmax (em): 508 nm) and acetonitrile (λmax (em): 420 nm) while cyclic p‐terphenyl 9 a showed blue fluorescence in chloroform and 1,4‐dioxane (λmax (em): 470 nm). Similarly, compound 11 a showed blue fluorescence in chloroform (λmax (em): 468 nm) and 1,4‐dioxane (λmax (em): 473 nm). Additionally, the thermal stability of synthesized cyclic p‐terphenyls 11 a, 11 c and 11 d were also studied using TG and DTA techniques.