C.-T. Lin et al. / Tetrahedron Letters 46 (2005) 5033–5037
5037
1.2
1
acidic
neutral
basic
0.8
0.6
0.4
0.2
0
550
300
350
400
450
500
600
Wavelength (nm)
Figure 7. UV spectra of 5 in neutral, acidic, and basic (gaseous ammonia) conditions.
12. Montes, I. F.; Burger, U. Tetrahedron Lett. 1996, 37,
1007–1010.
3. Conclusions
13. For preparation of 4: To a solution of 3 (1.82 g, 10 mmol)
and 4-dimethylaminobenzaldehyde (1.49 g, 10 mmol) was
added 2 N NaOH/MeOH (30 mL). This mixture was then
gently heated to 80 ꢁC for 24 h. After completion of the
reaction, the solvent was concentrated in vacuo. This dark
red mixture was poured into water. The solution was then
extracted with dichloromethane twice. The combined
organic extracts were dried over MgSO4, filtered, and
concentrated. The crude product was purified by column
chromatography (EtOAc–hexanes = 1:9) to give a red
A unique property of triketone functional group, that is,
sensitivity to pH, has been introduced for the first time
in the design and synthesis of two novel acidichromic
colorants. Both acidichromic colorants contain two
pH-sensitive functional groups and exhibit reversible
color changes from red to yellow under high pH condi-
tions and to colorless under low pH conditions. These
molecules may potentially function as pH sensors or
for use in chemical-switching systems. Further incorpo-
ration of electron withdrawing substituents like halo-
gens on the coumarin moiety of 5 to tune finely the
acidichromic property is currently underway.
1
solid 4 in 71% yield. Mp 154–155 ꢁC. H NMR (CDCl3,
300 MHz) d 18.49 (d, J = 0.9 Hz, 1H), 8.17 (dd, J = 15.6,
0.9 Hz, 1H), 8.12 (d, J = 15.6 Hz, 1H), 7.60–7.55 (m, 2H),
6.69–6.64 (m, 2H), 3.06 (s, 6H), 2.54 (s, 2H), 2.42 (s, 2H),
1.09 (s, 6H); 13C NMR (CDCl3, 75MHz) d 201.8, 196.1,
186.7, 152.5, 147.9, 131.5, 122.9, 116.3, 111.7, 110.2, 53.3,
49.2, 40.1, 30.4, 28.3. IR (KBr) m 2956, 1649, 1583, 1534,
1420, 1373, 1280, 1162, 959, 819 cmÀ1. HRMS (EI) calcd
for C19H23NO3 (M+), 313.1678, found 313.1679. Crystal-
lographic data (excluding structure factors) for 4 have
been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication number CCDC-
270989. These data can be obtained free of charge via
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; Fax: +44 1223 336033.
Acknowledgments
The authors would like to thank the National Science
Council of Republic of China, Taiwan for financially
supporting this research under Contract No. NSC 93-
2113-M-029-002. The referees are also appreciated for
their valuable comments.
References and notes
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hydroxychromen-2-one (100 mg, 0.5mmol) and 4-dimeth-
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J = 15.3 Hz, 1H), 8.09 (dd, J = 7.8, 1.8 Hz, 1H), 7.65
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