Synthesis of a solvent-sensitive highly fluorescent derivative of perfluorocyclopentene Zhan-Xian Li, Wei Sun, Yan-Feng Yue, Ming-Hua Zheng, Chun-Hu Xu, Jing-Yi Jin, Chen-Jie Fang and Chun-Hua Yan * Beijing National Laboratory for Molecular Sciences, State Key Lab of Rare Earth Materials Chemistry and Applications, PKU-HKU Joint Lab in Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing 100871, China Received 18 June 2007; revised 21 August 2007; accepted 24 August 2007 Available online 30 August 2007 Abstract—A solvent-sensitive highly fluorescent compound, N-[2-(1 0 ,3 0 ,4 0 ,4 0 ,5 0 ,5 0 -hexafluorocyclopentenyl)]-4-(5-methoxy-thiazol- yl)pyridine (1D) was synthesized as an unexpected product of the reaction of 4-bromo-5-methoxy-2-(4-pyridyl)thiazole (1B) with perfluorocyclopentene in the presence of n-BuLi. Primary mechanism of this reaction was proposed, and the photophysical prop- erties of 1D in different solvents were studied. Ó 2007 Elsevier Ltd. All rights reserved. Photo-switching systems are attracting more and more interest owing to their bistable states, which can be achieved under irradiation at particular wavelengths selectively and regularly. As thermally stable and high fatigue-resistant compounds, diarylethene derivatives with heterocyclic aryl groups have been explored exten- sively due to the remarkably different properties of open/closed isomers such as absorption spectra, 1 fluorescence spectra, 1b,2 refractive indices, 3 IR spectra, 4 oxidation/reduction potentials, 5 and so on. Particularly, the rational design and successful syntheses of asym- metric diarylethenes based on perfluorocyclopentene are important in modulating the properties of their bistable thermal states, which are crucial for realizing their practical applications in information storage, photo-switching devices, etc. 2c,d,5c,6 As a necessary step during the syntheses of these photoactive molecules, reactions between perfluorocyclopentene and bromine- substituted aromatic compounds play an important role, the general synthetic procedure of which is depicted in Scheme 1. 1b,7 In the present work, the reaction of 4-bromo-5-methoxy-2-(4-pyridyl)thiazole (1B) with perfluorocyclopentene in the condition as described afforded not only the desired compound 1-{4-[5-meth- oxy-2-(4-pyridyl)thiazolyl]}perfluorocyclopentene (1C), but also an unexpected product N-[2-(1 0 ,3 0 ,4 0 ,4 0 ,5 0 ,5 0 - hexafluorocyclopentenyl)]-4-(5-methoxy-thiazolyl)pyr- idine(1D). With discussing the reactions of its analogs under the same conditions, a reasonable explanation is proposed for the formation of 1D. Furthermore, 1D is a strong fluorophore in solution and its fluorescent properties are dependent significantly on solvents. 5-Methoxy-2-(4-pyridyl)thiazole (1A) and 1B were syn- thesized according to the modified method reported in the literature. 8 The total synthetic process of 1C 9 and 1D 10 is shown in Scheme 2 and the synthetic approaches were completed according to the reported recipe. 7 The possible mechanism is presented in Scheme 3. The for- mation of 1D might be ascribed to the enhanced nucleo- philicity of the nitrogen atom in the pyridyl group after treatment of 1B with n-BuLi. To study the formation mechanism of 1D, 4-bromo-5- methoxy-2-(2-pyridyl)thiazole (2B) 8 and 4-bromo-5- methoxy-2-(3-pyridyl)thiazole (3B) 8 were treated with 0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2007.08.086 Keywords: N-[2-(1 0 ,3 0 ,4 0 ,4 0 ,5 0 ,5 0 -Hexafluorocyclopentenyl)]-4-(5-meth- oxy-thiazolyl)pyridine; 4-Bromo-5-methoxy-2-(4-pyridyl)thiazole; Perfluorocyclopentene; Solvent-sensitive; Highly fluorescent. * Corresponding author. Tel./fax: +86 10 62754179; e-mail: yan@ pku.edu.cn Scheme 1. General procedure for reaction of perfluorocyclopentene and bromine-substituted aromatic compounds. Reaction conditions: (a) n-BuLi, THF, À78 °C ! rt. Tetrahedron Letters 48 (2007) 7675–7679