Protonation-induced Cyclization of 1,8-Bis(arylethynyl)anthraquinones: Monopyrylium Salt Formation and Intensification of Donor–Acceptor Interaction

Abstract

We previously reported protonation-induced double cyclization reaction of 1,4-Ar 2 Aq and 1,5-Ar 2 Aq (Ar 2 Aq: bis(arylethynyl)anthraquinone) with strong acid HX that generated the corresponding dipyrylium salts [1,4- DA, DAD, and ADA (D: donor; A: acceptor) types of compounds are exciting materials, 1 and have been intensively studied in terms of fundamental research as well as potential applications, such as nonlinear optics (NLOs) and organic electronics. The electronic structure of DA, DAD, and AD A molecules can be systematically tuned by external stimuli, 24 such as protons, photons, electrons, and magnetic fields. Recently, these molecules have received unprecedented attention because of their peculiar physical and electronic properties, which can be employed to achieve switching behavior in molecular devices. 5,6 Our recent studies have developed a new class of DA and DAD molecules, ArAq and Ar 2 Aq, where Ar represents an aryl group, such as ferrocenyl (Fc), 4-N,N-bis(4-methoxyphenyl)aminophenyl (Am), platinadithiolene, phenyl, m-tolyl, and ptolyl, and Aq indicates ethynylanthraquinone or diethynylanthraquinone (Schemes 1a1c). 712 This series of molecules underwent single and double intramolecular cyclization reactions to afford pyrylium and dipyrylium cations, respectively (Schemes 1a1c). For example, 1-ArAq gave rise to the pyrylium salt [1-ArPyl]X (X: counter anion) with a quadruply fused-ring structure, in which a cationic oxygen participated in the aromatic six-membered ring (Scheme 1a). 8 We have also described novel DAD molecules, 1,4-Ar 2 Aq and 1,5-Ar 2 Aq, which experienced unprecedented protonation-induced double cyclization reactions to yield the dipyrylium salts, [1,4-Ar 2 -Pyl 2 ]X 2 and [1,5-Ar 2 Pyl 2 ]X 2 (Schemes 1b and 1c).9,10 These compounds possessed new types of quintuply fused-ring structures, which were isoelectronic with benzo[e]pyrene and perylene-type skeletons with 20³ electrons.10 These doublycondensed phases showed unique physical, chemical, and magnetic properties. Our successful studies on DAD 1,4-Ar 2 Aq and 1,5-Ar 2 Aq systems have prompted us to examine the 1,8-Ar 2 Aq system (Scheme 1d). We note that we previously disclosed the protonation behavior of 1,8-Fc 2 Aq, 7b but we could not identify its chemical structure at that stage.In the present study, we report on the new 1,8-Ar 2 Aq type of molecules: a homodonor compound, 1,8-Am 2 Aq, and the first heterodonor one in the Ar 2 Aq series, 1,8-AmFcAq. We also address their protonation reactions, together with the exact structure of the protonated product of 1,8-Fc 2 Aq. All these D AD molecules undergo a protonation-induced single cyclization reaction with bis(trifluoromethanesulfon)imide (TFSIH) as a strong acid, so as to yield the corresponding pyrylium salts, [1,8-Ar 2 Pyl](TFSI). The synthesis, characterization, singlecrystal X-ray diffraction (XRD) analysis, and physical properties of 1,8-Ar 2 Aq and [1,8-Ar 2 Pyl]X (Ar = Am and Fc, X = TFSI and BF 4 ) are described in this paper.

Design and Synthesis of “Chloropicolinate Amides and Urea Derivatives” as Novel Inhibitors for Mycobacterium tuberculosis

“…The DCM layer was dried with sodium sulfate and filtered, and solvent was removed under vacuum. The crude product was purified using column chromatography with EtOAc/Hexane (30:70) as a white solid, 72% yield; mp 284−287 °C; Methyl-4-amino-3-chloro-6-(2-((4-fluorophenyl) sulfonamido) phenyl) picolinate (26). The compound 7 (30 mg, 0.11 mmol) was dissolved in DCM (3 mL) solvent, and DIPEA (23 μL, 0.13 mmol) and 4-fluoro benzenesulfonylchloride (21 mg, 0.11 mmol) were added simultaneously and stirred for 4 h at RT.…”

“…Besides, one of the major research area for our group is to design and synthesize a new heterocyclic scaffold containing compounds for novel biological activity and material applications. 8 , 19 − 26 …”

“…With this strategy, we designed 30 new heterocyclic scaffolds that could be synthesized by treating methyl 4-amino-6-(2-aminophenyl)-3-chloropyridine-2-carboxylate with different acid chloride, urea, and thiourea moieties. Besides, one of the major research area for our group is to design and synthesize a new heterocyclic scaffold containing compounds for novel biological activity and material applications. ,− …”

Fundamental and Applied Aspects of the Chemistry of Acetylenylquinones

“…In a series of studies, Japanese scientists reported the electrophilic cyclization of 1-aryl ethynylanthra-quinones [16][17][18]. Here, protonation was performed on a wide range of substrates via the addition of bis(trifluoromethanesulfone)imide acid (TFSIH) in dichloromethane to give products that were stable in air.…”

Design and Synthesis of Antimicrobial Active (E)‐(3‐(Substituted‐styryl)‐7H‐furo[2,3‐f]chromen‐2‐yl)(phenyl)methanone Derivatives and Their In Silico Molecular Docking Studies

“…On the other hand, benzofuran derivatives are also present in many natural products and exhibit properties like physiological, pharmacological, and toxic. They also display many applications like sedatives, antioxidants , pharmaceuticals , cosmetics , molecular switches , and also for the building blocks of optical brighteners . In fact, several benzofuran ring systems bearing various substituents at the C‐2 position are widely distributed in nature.…”