Paper
Palladium-catalyzed synthesis of 7,9-diaryl-8 H-acenaphtho[1,2-c]pyrroles and their application in explosives detection.
Published Aug 29, 2011 · Xiaopeng Chen, Jisong Jin, Yanguang Wang
Chemistry
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Abstract
Pyrrole is one of the most important heterocyclic compounds in nature. Its derivatives are broadly found and developed as drugs in medicinal industry. Meanwhile, they are closely related to optoelectronic material fields, such as pyrrole-based oligomer or organic field-effect transistors (OFET). To satisfy the booming request of pharmaceutical and material applications of various pyrroles, synthetic approaches of either pyrrole construction or pyrrole modification have attracted considerable attention for achieving an ideal state that fulfils reactions with multiple advantages: readily available starting materials, simple processing, and high economical and ecological values. On the other hand, explosives detection is of importance in military operation, public safety, and environmental cleaning. Several attempts have thereafter been made and tested to be practical. For example, Swager and co-workers reported the detection of nitroaromatic explosives in the vapor phase using fluorescent quenching of conjugated polymers. It offered a simple, exquisitely sensitive, and rapid detection of explosives in the vapor phase. The mechanism of fluorescence quenching for explosives detection was attributed to the photoinduced electron-transfer from the excited polymer donor to the explosive acceptors. With rigid parallel triple bonds in a molecule, the reactivity of diynes was greatly enhanced due to the existence of the orbital repulsion between two triple bonds and the resulting bend of the triple bonds. By this consideration, a series of products might be constructed by sequential reactions from 1,8-diarenynyl naphthalenes in which the triple bonds were fixed and influenced by each other. In this communication, we tested the reaction of 1,8-diphenylacetylenyl naphthalene (1 a) with aniline (2 a) in the presence of PdCl2. To our delight, 8H-acenaphthoACHTUNGTRENNUNG[1,2-c]pyrrole (3 a) was easily constructed and its structure was established by using X-ray crystal analysis. To efficiently perform this reaction, we optimized the reaction conditions for this transformation. The reactivity largely depended on the solvent; when the reaction was catalyzed by palladium(II) chloride, only dimethylsulfoxide (DMSO) gave the desired product (Table 1, entries 1–5). Other polar aprotic solvents, such as, dimethylforamide, acetonitrile, nitromethane, and nitrobenzene did not facilitate the reaction and no desired product could be detected. By altering DMSO to sulfolane (Table 1, entry 6), 3 a was also obtained, but in relatively lower yield. When the base additive was added, the yields of the isolated product were increased (Table 1, entries 1 and 7–10). Triethylamine provided the best yield among other bases, such as sodium carbonate, potassium carbonate, diisopropylethylamine, and triethylamine. Similarly, the use of sulfolane as a solvent also afforded 3 a upon addition of triethylamine (Table 1, entry 11). Decreasing the reaction temperature to 60 8C, the yield of the isolated product was determined to be 23 %, although 1 a completely disappeared based on tracking by TLC (Table 1, entry 12). Altering the palladium to other Pd sources, such as PdBr2 and Pd ACHTUNGTRENNUNG(OAc)2, comparative
Palladium-catalyzed synthesis of 7,9-diaryl-8 H-acenaphtho[1,2-c]pyrroles offers a promising method for explosives detection, with potential applications in pharmaceutical and optoelectronic material fields.
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