Metal‐Free Synthesis of Thermally Stable Fluorescent p‐Terphenyls by Ring Transformation of 2H‐Pyran‐2‐ones. Issue 25 (2nd July 2020)

• Record Type: Journal Article
• Authors: Chandrasekar, Subashini; Singh, Fateh V.
• Is Part Of: ChemistrySelect. Volume 5:Issue 25(2020)
• Page Start: 7452
• Page End: 7459
• Publication Date: 2020-07-02
• Subjects: cyclic p-terphenyls -- carbanion -- 2H-pyran-2-one -- Nucleophilic addition -- ring transformation reaction; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.202001502
• Languages: English
• ISSNs: 2365-6549

Abstract

Abstract: A 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‐2 H ‐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. Abstract : A simple and convenient route for the synthesis of cyclic and acyclic para ‐terphenyls was described through carbanion‐induced ring transformation of 2 H ‐pyran‐2‐ones under mild reaction conditions. The potential of the method lies in generating p ‐terphenyls functionalized with different electron donating and withdrawing functionalities in terphenyls architecture. Moreover, the photo‐physical behaviour of synthesized p ‐terphenyls was studied using UV‐visible and Fluorescence Spectroscopy. Additionally, the thermal stability of cyclic p ‐terphenyls was also studied using TG and DTA techniques.