4
Tetrahedron Letters
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In the anodic region, oxidation peaks were observed in
compounds 3h and 3i within the 0.8 to 0.9 V potential range, and
this can be attributed to the reoxidation of the naphthyridine’s
heterocyclic skeleton, coordinated to the BF2 moiety.
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Table 2. Redox potential data for compounds 3a–i.
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Jaggi, M. Arch. Pharm. Chem. Life Sci. 2015, 348, 837-860.
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2012, 10, 2578-2589.
Compd.
3a
R
R1
H
E1 (V)
-1.533a
-1.673a
-1.948a
-1.681a
-1.869a
-1.872a
-1.580a
-1.818a
-1.690a
E2 (V)
-----
E3 (V)
------
------
------
-----
C6H5
13. Hikishima, S.; Minakawa, N. Kuramoto, K.; Fujisawa, Y.; Ogawa,
M.; Matsuda, A. Angew. Chem., Int. Ed. 2005, 44, 596-598.
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Ji. J. F.; Hao, R. T.; Zhang, J. F.; Zhou, Y. Tetrahedron Lett. 2015,
56, 5034-5038.
3b
4-CH3C6H4
4-FC6H4
H
-----
3c
H
-----
3d
4-BrC6H4
4- OCH3C6H4
4- NO2C6H4
2- Thienyl
4- OCH3C6H4
4- NO2C6H4
H
-----
3e
H
-----
-----
3f
H
-1.528a
+0.831b
-1.584a
+0.815b
-----
17. Smart, B. E. J. Fluorine Chem. 2001, 109, 3-11.
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Fu, W-F. Org. Lett. 2012, 14, 5226-5229.
3g
H
-----
19. Eichler, E.; Rooney, C. S.; Williams, H. W. R. J. Heterocycl.
Chem. 1976, 13, 41-42.
3h
NMe2
NMe2
+0.827b
20. Bonacorso, H. G.; Andrighetto, R.; Krüger, N.; Zanatta, N.;
Martins, M. A. P. Molecules, 2011, 16, 2817-2832.
3i
-----
21. Quan, L. Chen, Y.; Lv, X-J.; Fu, W-F. Chem. Eur. J. 2012, 18,
14599-14604.
aCathodic peak, bAnodic peak, *Fc+/Fc redox couple pair in DCM -E1/2 = 0.5
V.
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Fisher, J. Turnbull, W. B. Wilson, J. A. Chem. Eur. J. 2011, 17,
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In conclusion, we presented a highly regioselective synthesis,
11B- and 19F-NMR spectroscopy, and the optical and
electrochemical properties of a series of nine new fluorescent
trifluoromethylated organoboron derivatives, which were
synthesized and easily purified at good yields. The 1,8-
naphthyridine-BF2 complexes 3a–i showed moderate quantum
yields, and the best Stokes shifts were found in the compounds
that contain electron-donating substituents (3e and 3g) and those
with a strong push-pull system (3h and 3i). This is an initial
study of the potential of these new complexes which have
possible application in materials science. The electronic effect of
some other substituents and other physical-chemical properties
will be studied in the near future.
23. General procedure for the preparation of complex 1,8-
naphthyridine-BF2 3a-i: Solutions of the respective amides 2a-i (3
mmol), BF3•Et2O (6.0 mL) and anhydrous triethylamine (4.5 mL)
in anhydrous chloroform (60 mL) were magnetic stirring for 24 h
at room temperature. After the end of the reactions (TLC), the
mixtures were extracted with dichoromethane (3 x 20 mL) and
water (3 x 20 mL). The organic phase of each reaction was dried
over anhydrous Na2SO4, and the solvent was evaporated under
reduced pressure. The crude products 3a-i were purified by
column chromatography on silica gel using dichloromethane as
the eluent. Data for 1,1-difluoro-3,9-diphenyl-7-(trifluoromethyl)-
1H-[1,3,5,2]oxadiazaborinino[3,4-a][1,8]naphthyridin-11-ium-1-
uide (3a): yellow solid, yield 58 %, mp 225 – 227 °C. 1H NMR
(400 MHz, CDCl3) δ (ppm): 8.57 (d, J = 9 Hz, 1H, H-5), 8.46 (d, J
= 8 Hz, 2H, H-6 and Ph), 8.41 (d, J = 8 Hz, 2H, Ph), 8.30 (s, 1H,
H-8), 7.65 (t, J = 7 Hz, 1H, Ph), 7.59 -7.56 (m, 4H, Ph), 7.53 (t, J
= 8 Hz, 2H, Ph). 13C NMR (100 MHz, CDCl3): δ (ppm): 169.3 (C-
3), 160.3 (C-10a), 159.3 (C-9), 149.4 (C-6a), 138.5 (C-4a), 136.2
(q, 2J = 32 Hz, C-7), 136.1 (C-Ph), 134.3 (C-6), 131.9 (C-Ph),
131.7 (C-Ph), 130.4 (C-Ph), 129.4 (C-Ph), 128.6 (C-Ph), 128.2 (C-
Ph), 124.5 (Ph), 122.6 (q, 1J = 275 Hz, CF3), 115.7 (q, 3J = 5
Hz,C-8), 114.9 (C-5).19F NMR (564 MHz, CDCl3): δ (ppm): -
60.56 (CF3), -130.18 , -130.20 (BF2). 11B NMR (192 MHz,
CDCl3): δ (ppm): 1.21. Anal. Calcd. For C22H13BF5N3O: C, 59.90;
H, 2.97; N, 9.52. Found : C, 60.06 ; H, 2.98; N, 9.38.
Acknowledgments
The authors thank the Coordination for Improvement of
Higher Education Personnel (CAPES) for the fellowships, as
well as the National Council for Scientific and Technological
Development (CNPq) — process number 306.883/2015-5 and
PVE 401193/2014-4 — and the Rio Grande do Sul and Minas
Gerais Foundations for Research Support (FAPERGS and
FAPEMIG) for financial support.
24. The crystallographic data for the structure of 3g have been
deposited with the Cambridge Crystallographic Data Centre and
allocated the deposition number CCDC 1497181. Copies of the
data can be obtained free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax:+44 1223336033 or
deposit@ccdc.com.ac.uk).
Supplementary data
Supplementary data associated with this article can be found,
in the online version, at………
25. Xie, X.; Yuan, Y.; Krüger, R.; Bröring, M. Magn. Reson. Chem.
2009, 47, 1024-1030.
References and notes
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