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

Abstract

A metal-free approach for the synthesis of p-terphenyls 7 a-i and cyclic p-terphenyls 9 ad and 11 ad 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 (λ max (em): 508 nm) and acetonitrile (λ max (em): 420 nm) while cyclic p-terphenyl 9 a showed blue fluorescence in chloroform and 1,4-dioxane (λ max (em): 470 nm). Similarly, compound 11 a showed blue fluorescence in chloroform (λ max (em): 468 nm) and 1,4-dioxane (λ max (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.

Metal free synthesis of thermally stable blue fluorescent m-terphenyls by ring transformation of 2H-pyran-2-ones: chemical synthesis, spectroscopy and computational studies

“…38,39 Besides, the 2H-pyran-2-one was reacted with various secondary amines in methanol at reux temperature to achieve the synthesis of 4amino-6-biphenyl-2H-pyran-2-ones. 40,41 Our earliest efforts were dealt with the screening of suitable base for the ring transformation of 6-([1,1 0 -biphenyl]-4-yl)-2-oxo-4-(piperidin-1-yl)-2H-pyran-3-carbonitrile 9a. The bases of different pK b in DMF have been used for the ring transformation of substrate 9a to corresponding biphenyl anked Vshaped m-terphenyls derivatives 11a-h using ketone 10 as a source of carbanion and results are outlined below (Table 1).…”

“…38,39 Besides, the 2 H -pyran-2-one was reacted with various secondary amines in methanol at reflux temperature to achieve the synthesis of 4-amino-6-biphenyl-2 H -pyran-2-ones. 40,41…”

Synthesis of fluorescent aromatic species via ring transformation of α-pyranones and their application in OLEDs, chemosensors, and cell imaging

“…Specifically, the synthesis of p -terphenyls 20 and cyclic terphenyls 22 that displayed cyan ( λ em = 508 nm) and blue ( λ em = 468–470 nm) fluorescence in chloroform was detailed. 61 The process involved stirring 4-amino-6-([1,1′-biphenyl]-4-yl)-3-cyano-2 H -pyran-2-ones 18 with malononitrile 19 in DMF at room temperature, using KOH as a base to obtain p -terphenyls 20 and employing cyclohexanone 21 for cyclic terphenyls 22 (Scheme 6).…”

Transition-metal-free synthesis and photophysical studies of highly functionalized (E)-stilbenes

“…The well-known methods to synthesize stilbene derivatives include transition metal couplings, such as Sonogashira, Mizoroki-Heck, Negishi, Suzuki-Miyaura, Stille, Grubbs & McMurry, Knoevenagel-Doebner, Wittig, or Horner-Wadsworth-Emmons (HWE) olefination, Ramberg-Bucklund reactions, and Perkin aldol condensation. [36][37][38] In the course of our continuous investigation into substituted aromatic systems involving donors and acceptors, [39][40][41][42][43][44][45][46] we have devised an efficient approach to craft donor-acceptor p-conjugated (D-p-A) stilbenes. In this molecule, the secondary amine at the C4 position acts as the donor group and the CN group acts as the acceptor functionality.…”

“…In the course of our continuous investigation into substituted aromatic systems involving donors and acceptors, 39–46 we have devised an efficient approach to craft donor–acceptor π-conjugated (D–π–A) stilbenes. In this molecule, the secondary amine at the C4 position acts as the donor group and the CN group acts as the acceptor functionality.…”