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Synlett 2010(1): 89-92  
DOI: 10.1055/s-0029-1218535
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Novel Rhodamine Dyes via Suzuki Coupling of Xanthone Triflates with Arylboroxins

Brandon D. Calitree, Michael R. Detty*
Department of Chemistry, University at Buffalo, 627 Natural Sciences Complex, North Campus, The State University of New York, Buffalo, NY 14260-3000, USA
Fax: +1(716)6456963; e-Mail: mdetty@buffalo.edu;
Further Information

Publication History

Received 28 September 2009
Publication Date:
02 December 2009 (online)

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Abstract

Novel rhodamine dyes were prepared from xanthone precursors in a ‘one-pot’ procedure via reaction of the xanthone with trifluoromethanesulfonic anhydride followed by Pd-mediated Suzuki coupling between the xanthone triflate and an arylboroxin. Rhodamines with 9-(3- or 4-carboxyphenyl) and 9-(3-nitrophenyl) substituents were prepared by this procedure. The procedure also works well with thio- and selenoxanthones, but not with telluroxanthones.

Key words

Suzuki coupling - arylations - palladium - rhodamine dyes - arylboroxins

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Trifluoromethanesulfonic anhydride (61.7 µL, 0.367 mmol, 1.1 equiv) was added to 3,6-dimethylaminoxanth-9-one 1-E (1.0 equiv 0.334 mmol) in MeCN (15 mL). The resulting solution was stirred for 20 min at ambient temperature. PdCl2(PPh3)2 (23 mg, 0.033 mmol, 0.1 equiv), Na2CO3 (106 mg, 1.00 mmol, 3.0 equiv), and arylboroxin 4 (0.334 mmol, 1.0 equiv) were added, and the temperature was increased to 55 ˚C. The reaction was monitored by visible spectroscopy for the appearance of the dye chromophore and disappear-ance of the chromophore of triflate 2-E (20 min for 7-S to
4.5 h for 8-S). The reaction mixture was cooled to ambient temperature, and H2O (15 mL) was added. The dye was extracted with CH2Cl2 (5 × 20 mL), and the combined extracts were concentrated onto SiO2 and dry loaded onto
a column of SiO2. A gradient elution system (10% Et2O-CH2Cl2, 40% Et2O-CH2Cl2, 5% MeOH-CH2Cl2, and 10% MeOH-CH2Cl2) separated recovered starting material from rhodamine/rosamine dye isolated as a mixture of triflate and boronate salts. The dye was dissolved in AcOH (3 mL), and 30% HPF6 or concentrated HCl was added dropwise until the characteristic color of the rhodamine/rosamine faded. The reaction mixture was poured into stirring ice H2O, and the dye was collected by filtration. The ion exchange was repeated for a total of 3 times. The success of the ion exchange was confirmed by elemental analysis (±0.4% in C, H, N).

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Analytical Data for 8-O
Mp >260 ˚C. ¹H NMR (500 MHz, CD2Cl2): δ = 8.35 (d, 2 H, J = 8.0 Hz), 7.47 (d, 2 H, J = 8.0 Hz), 7.41 (d, 2 H, J = 9.5 Hz), 6.96 (dd, 2 H, J = 2.0, 9.5 Hz), 6.82 (d, 2 H, J = 2.0 Hz), 3.31 (s, 12 H). ¹³C NMR (75.5 MHz, CD3OD): δ = 168.7, 159.2, 159.0, 158.1, 137.9, 133.8, 132.5, 131.1, 131.0, 115.8, 114.3, 97.7, 41.0. UV/vis: λmax (CH2Cl2) = 568 nm (ε 1.10˙105 M-¹ cm-¹). ESI-HRMS: m/z calcd for C24H23N2O3 +: 387.1703; found: 387.1720.
Analytical Data for 8-S
Mp >260 ˚C. ¹H NMR (500 MHz, CD3OD): δ = 8.17 (d, 2 H, J = 7.0 Hz), 7.36 (d, 2 H, J = 7.0 Hz), 7.28 (d, 2 H, J = 9.5 Hz), 7.24 (d, 2 H, J = 2.5 Hz), 7.01 (dd, 2 H, J = 2.5, 9.5 Hz), 3.19 (s, 12 H). ¹³C NMR (75.5 MHz, CD3OD): δ = 160.3, 154.2, 144.9, 139.3, 136.9, 130.5 (br, 2 C), 129.7, 119.4, 115.9, 106.0, 40.8. UV/vis: λmax (MeOH) = 582 nm (ε 7.91˙104 M-¹ cm-¹). ESI-HRMS: m/z calcd for C24H23N2O2S+: 403.1475; found: 403.1468.
Analytical Data for 9-O
Mp >260 ˚C. ¹H NMR (500 MHz, CD3OD): δ = 8.24 (d, 1 H, J = 8.0 Hz), 8.00 (s, 1 H), 7.72 (t, 1 H, J = 7.5 Hz), 7.62 (d, 1 H, J = 7.5 Hz), 7.26 (d, 2 H, J = 9.0 Hz), 7.03 (dd, 2 H, J = 2.0, 9.0 Hz), 6.91 (d, 2 H, J = 2.0 Hz), 3.23 (s, 12 H). ¹³C NMR (75.5 MHz, CD2Cl2/CD3OD): δ = 168.4, 159.0, 158.6, 158.0, 134.5, 133.4, 132.3, 132.2, 131.4, 131.2, 130.1, 115.4, 114.4, 97.5, 41.0. UV/vis: λmax (MeOH) = 562 nm (ε 1.03˙106 M-¹ cm-¹). ESI-HRMS: m/z calcd for C24H23N2O3 +: 387.1703; found: 387.1704.
Analytical Data for 9-S
¹H NMR (500 MHz, CD3CO2D/CD2Cl2): δ = 8.31 (d, 1 H, J = 7.5 Hz), 8.02 (s, 1 H), 7.74 (t, 1 H, J = 7.5 Hz), 7.60 (d, 1 H, J = 7.5 Hz), 7.32 (d, 2 H, J = 9.5 Hz), 7.20 (d, 2 H, J = 2.0 Hz), 6.95 (dd, 2 H, J = 2.0, 9.5 Hz), 3.25 (s, 12 H). ¹³C NMR (75.5 MHz, CD3OD): δ = 160.6, 154.7, 145.4, 137.2, 136.5, 132.9, 131.4, 131.2, 129.5, 119.9, 116.3, 106.5, 40.8. UV/vis: λmax (MeOH) = 579 nm (ε 7.26˙104
M-¹ cm-¹). ESI-HRMS: m/z calcd for C24H23N2O2S+: 403.1475; found: 403.1467.
Analytical Data for 10-O
¹H NMR (500 MHz, CD2Cl2): δ = 8.53 (dd, 1 H, J = 2.0, 8.0 Hz), 8.28 (t, 1 H, J = 2.0 Hz), 7.91 (t, 1 H, J = 8.0 Hz), 7.81 (d, 1 H, J = 8.0 Hz), 7.27 (d, 2 H, J = 9.0 Hz), 6.98 (dd, 2 H, J = 2.0, 9.0 Hz), 6.88 (d, 2 H, J = 2.0 Hz), 3.32 (s, 12 H). ¹³C NMR (75.5 MHz, CD2Cl2): δ = 158.1, 157.8, 154.8, 148.7, 135.9, 131.4, 131.0, 125.4, 124.6, 115.1, 113.7, 97.2, 41.3. UV/vis: λmax (CH2Cl2) = 574 nm (ε 6.77˙104 M-¹ cm-¹). ESI-HRMS: m/z calcd for C23H22N3O3 +: 388.1656; found: 388.1660.
Analytical Data for 10-S
Mp >260 ˚C. ¹H NMR (500 MHz, CD2Cl2): δ = 8.50 (dt, 1 H, J = 1.0, 8.0 Hz), 8.20 (s, 1 H), 7.90 (t, 1 H, J = 8.0 Hz), 7.73 (d, 1 H, J = 8.0 Hz), 7.28 (d, 2 H, J = 9.0 Hz), 7.17 (d, 2 H, J = 2.0 Hz), 6.97 (dd, 2 H, J = 2.0, 9.0 Hz), 3.29 (s, 12 H). ¹³C NMR (75.5 MHz, CD2Cl2): δ = 156.5, 153.9, 148.6, 144.7, 137.5, 136.0, 135.8, 130.8, 124.7, 124.4, 119.0, 116.1, 106.2, 41.0. UV/vis: λmax (CH2Cl2) = 593 nm
(ε 1.02˙105 M-¹ cm-¹). ESI-HRMS: m/z calcd for C23H22N3O2S+: 404.1427; found: 404.1420.