Convenient Synthesis of Isocyanate and Isothiocyanate-Substituted Boron Dipyrromethene Dyes and Derivatives

Abstract

Starting from nitro-substituted phenyl rings, the preparation of boron dipyrromethene dyes carrying amino functions was achieved in good yields. Conversion of the p-aminophenyl group to the corresponding isocyanate and isothiocyanate is feasible under mild conditions. Various combinations allow the production of luminescent molecules bearing mono- or disubstituted urea or thiourea substituents. When two adjacent amino functions are present, a simple protocol allows the production of pyridine-indole and dipyridophenazine derivatives. The on/off switching of the fluorescence from the nitro to the amino and further to the urea renders these dyes attractive as fluorescent probes.

boron - amines - reduction - isocyanate - fluorescence

References and Notes

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16 Selected data for 7: isolated yield quantitative. ¹H NMR (CDCl₃): δ = 7.23 (m, 4 H), 2.53 (s, 6 H), 2.30 (q, 4 H, ³ J = 7.5 Hz), 1.31 (s, 6 H), 0.98 (t, 6 H, ³ J = 7.5 Hz) ppm. ¹³C NMR (CDCl₃): δ = 154.3, 138.9, 138.2, 134.3, 133.6, 133.2, 130.9, 130.0, 129.7, 125.6, 17.2, 14.7, 12.7, 12.0 ppm.

17

Selected data for 8: isolated yield quantitative. ¹H NMR (CDCl₃): δ = 7.32 (m, 4 H), 2.53 (s, 6 H), 2.30 (q, 4 H, ³ J = 7.5 Hz), 1.30 (s, 6 H), 0.98 (t, 6 H, ³ J = 7.5 Hz) ppm. ¹³C NMR (CDCl₃): δ = 154.5, 138.4, 138.1, 137.2, 135.1, 133.3, 132.3, 130.7, 130.1, 126.5, 17.2, 14.7, 12.7, 12.1 ppm.

18

Selected data for 12: 99%. ¹H NMR (CDCl₃): δ = 7.51 (d, 2 H, ³ J = 8.5 Hz), 7.39-7.32 (m, 4 H), 7.18-7.15 (m, 3 H), 7.00 (br s, 1 H), 6.84 (br s, 1 H), 2.53 (s, 6 H), 2.28 (q, 4 H, ³ J = 7.5 Hz), 1.33 (s, 6 H), 0.96 (t, 6 H, ³ J = 7.5 Hz) ppm. ¹³C NMR (CDCl₃): δ = 153.8, 153.0, 140.1, 139.2, 138.6, 137.9, 133.0, 131.2, 130.6, 129.6, 129.2, 124.8, 121.6, 119.9, 17.2, 14.7, 12.7, 12.1 ppm. ¹¹B NMR (CDCl₃): δ = 3.93 (t, ¹ J = 32 Hz) ppm. FAB⁺-MS: m/z (nature of peak, rel. intensity) = 515.2 (100) [M + H]⁺. Anal. Calcd for C₃₀H₃₃BF₂N₄O·H₂O: C, 67.67; H, 6.63; N, 10.52. Found: C, 67.52; H, 6.52; N, 10.32.

19

Selected data for 13: 60%. ¹H NMR (CDCl₃): δ = 7.94 (br s, 1 H), 7.81 (br s, 1 H), 7.58 (dd, 2 H, ¹ J = 1.7 Hz, ³ J = 6.6 Hz), 7.51-7.45 (m, 2 H), 7.39-7.32 (m, 3 H), 7.30-7.28 (dd, 2 H, ¹ J = 1.7 Hz, ³ J = 6.6 Hz), 2.52 (s, 6 H), 2.29 (q, 4 H, ³ J = 7.5 Hz), 1.32 (s, 6 H), 0.97 (t, 6 H, ³ J = 7.5 Hz) ppm. ¹³C NMR (CDCl₃): δ = 180.0, 154.1, 139.1, 138.5, 138.3, 136.5, 134.0, 133.1, 130.9, 130.3, 129.4, 127.8, 124.4, 125.1, 17.2, 14.7, 12.7, 12.1 ppm. ¹¹B NMR (CDCl₃): δ = 3.85 (t, ¹ J = 32 Hz) ppm. FAB⁺-MS: m/z (nature of peak, rel. intensity) = 531.1 (100) [M + H]⁺. Anal. Calcd for C₃₀H₃₃BF₂N₄S·H₂O: C, 65.69; H, 6.43; N, 10.21. Found: C, 65.49; H, 6.28; N, 9.93.

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