Replacement of the Hetarene Moiety of Molecule in the Synthesis of Indoline Spiropyran with Cationic Fragment
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Replacement of the Hetarene Moiety of Molecule in the Synthesis of Indoline Spiropyran with Cationic Fragment A. D. Pugacheva,*, M. B. Lukyanovaa, B. S. Lukyanova, I. V. Ozhogina, A. S. Kozlenkoa, V. V. Tkachevb,c, P. B. Chepurnoia, G. V. Shilovb, Academician V. I. Minkina, and Academician S. M. Aldosinb Received March 11, 2020; revised May 26, 2020; accepted July 19, 2020
Abstract—The paper describes the preparation of a new salt spiropyran of indoline series containing vinyl3H-indolium fragment in the 8' position of the 2H-chromene moiety and a chlorine atom in the benzene ring of the indoline fragment. The structure of the reaction product was studied by IR, 1H, and 13C NMR spectroscopy. The data of X-ray diffraction study indicate that the reaction leads to the partial exchange of the indoline hetarene fragment to provide previously described salt spiropyran containing no chlorine atom in the indoline portion of the molecule. Keywords: spiropyrans, heterocycles, NMR, X-ray diffraction, single crystal, organic synthesis, one-pot synthesis, indoline, 2H-chromene DOI: 10.1134/S0012500820350013
Spiropyrans constitute one of the most studied classes of organic photochromic compounds [1]. The possibility to control molecule characteristics provides a wide application of this class of compounds in different fields of science and technology [2–4].
The previously failed attempt [9] to synthesize spiropyran 3 from 1,3,3,6'-tetramethyl-5-chlorospiro[indoline-2,2'-2H-chromene] 4 (Scheme 2) is likely to be due to the lower reactivity of the formyl group of spiropyran in it than in 2-hydroxy-3-formyl5-methylbenzaldehyde (2) on the one hand, and the negative effect of the chlorine atom in the benzene ring of 1,2,3,3-tetramethyl-5-chloro-3H-indolium perchlorate (1) on the reactivity of the methyl group in the 2-position, on the other hand. Therefore, we used a two-step procedure to obtain a new salt spiropyran containing only one chlorine atom (in the indoline moiety) using 1,2,3,3tetramethyl-3H-indolium salts 1 and 5 of different structure (Scheme 3). Reaction products were studied by IR spectroscopy and 1H and 13C NMR. The IR spectrum of compound 4 shows, in addition to the C=C (1608 cm–1), Car–N (1291, 1258 cm–1), Cspiro–O (927 cm–1), and C–Cl (730 cm–1) bands, the C=O absorption band at 1693 cm–1; the 1H and 13C NMR spectra correspond to structure 4. The IR spectra of spiropyran 6 show characteristic absorption bands corresponding to the C=C (1605 cm–1) and C–N (1308 and 1260 cm–1) stretching vibrations, the Cl=O stretching mode of perchlorate anion (1091 cm–1), Cspiro–O (931 cm–1), as well as C–Cl stretches (1021 and 760 cm–1). However, 1H NMR spectrum has a complex profile indicating the presence of two compounds of similar structure. In compound 6, the gem-dimethyl groups of
The salt forms of spirocyclic compounds are of interest for pharmaceutics [5]. It is believed that salt spiropyrans can show photochromic behavior in solid state due to the presence of the bulky counterion in crystal lattice. The replacement
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