L. Wirtz, U. Kazmaier
SHORT COMMUNICATION
ment towards biomolecules or drug molecules for biological
and medicinal studies.
Experimental Section
General Procedure for the ClTi(OiPr)3-Catalyzed Pechmann Con-
densations: A 1 m solution of ClTi(OiPr)3 (2 mL, 2.0 mmol) was
added to a suspension of 8-hydroxyjulodin (189 mg, 1.0 mmol) and
the corresponding β-oxo ester (1.0 mmol) in toluene (3 mL). The
mixture was heated to reflux overnight. After cooling to room tem-
perature, CH2Cl2 (10 mL) was added, and the whole solution was
poured into a stirred satd. potassium sodium tartrate solution
(10 mL) until the phases separated. The aqueous layer was ex-
tracted thrice with CH2Cl2. The combined organic layers were
dried (Na2SO4), and the solvent was removed in vacuo. The residue
was dissolved in EtOH and covered with a layer of hexane. After
storage for 3 d in a refridgerator, the precipitate was recrystallized
from EtOH providing the required coumarin derivatives as yellow
solids.
Scheme 3. Modification of functionalized coumarins.
Table 3. Spectroscopical data of compounds 2–6 in DMSO.
Coumarin λex [nm] λem [nm] λem – λex [nm] Quantum yield
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures and analytical data for all new com-
2a
2b
2f
2g
2h
3a
3b
3c
3d
3e
4
391
394
391
389
377
389
389
389
370
389
404
410
400
400
456
460
454
454
–
454
460
454
457
464
476
457
453
495
65
66
63
65
–
65
71
66
87
76
72
47
53
95
1.05
1.13
1.00
1.00
–
1.00
1.05
1.01
1.09
1.13
1.10
1.02
0.86
0.88
1
pounds, including copies of fluorescence, H and 13C NMR spec-
tra.
Acknowledgments
Financial support by the Deutsche Forschungsgemeinschaft is
gratefully acknowledged. We also thank Prof. G. Jung, C. Spieß
and D. Auerbach for supporting us with the fluorescence spectra
and quantum yields.
5
6a
6b
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In general, the color and the maxima of the fluorescence
spectra depend on the solvent used (solvatochromy). To
prove also this solvatochromic effect for our new fluoro-
phores, we exemplarily investigated a solution of 2a in dif-
ferent solvents (Table 4). By switching from apolar solvents
to very polar ones a continuous shift towards higher wave-
lengths was observed for the emission spectra. By far the
largest Stokes shift was observed in H2O.
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Table 4. Solvatochromic effect on photophysical properties of 2a.
Solvent
λex [nm]
λem [nm]
λem – λex [nm]
CH2Cl2
DMSO
EtOH
MeOH
H2O
387
389
389
393
399
422
454
461
473
503
55
65
72
80
104
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Conclusions
We have shown that the ClTi(OiPr)3-catalyzed Pechmann
condensation is a relatively mild procedure, which allows
the synthesis of fluorogenic amino-substituted coumarin
derivatives in consistently good yields. Amino- and car-
boxy-substituted side chains should allow an easy attach-
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