Suraj Mal

1.6. Isoxazolones as sensitizers
1.6.1. General Properties of Isoxazolones
Isoxazolones, acylated/aroylated derivatives of isoxazole is another class of 1,3-dicarbonyl
compounds is well known as antenna chromophore for lanthanide ions 99 . The photophysical
characteristics of isoxazolones varies depending on the 3-substituted site which makes them
potential materials due to extended electronic conjugation. Isoxazolones are generally soluble
in organic media (non-polar and polar solvents) with thermal decomposition at 140-200 0 C.
Due to the presence of two oxygen donor atoms and facile keto-enol tautomerism, they can
easily coordinate with metal ions after deprotonation of the enolic hydrogen and provide
stable cationic complexes with six-membered chelate rings.
The complexes of isoxazolonates possess high thermal stability and display interesting
luminescence, nonlinear optical, and electrochemical properties. The excellent coordination
ability caused by the presence of 1,3-dicarbonyl unit act as bridging building block in supra-
molecular assemblies. Isoxazolones have strong UV absorption within large wavelength
range for its π-π* transition, and consequently has been targeted from its ability to sensitize
the luminescence of Ln(III) ions.
1.6.2. Synthetic approach for substituted isoxazolone
The substrate 3-phenylisoxazol-5(4H)-one can be acylated at different position (O, N or C)
under different reaction conditions. With aliphatic acyl groups N-acylation can be easily
achieved while aromatic acid chlorides are more likely to form O-acylated product. The
Schotten-Baumann procedure gave the best ratio of N- to O-acylated materials but with low
reaction yield presented in figure 1.29. The substrate 3-phenylisoxazol-5(4H)-one has the
possibility of undergoing C-acylation at C-4 only if acid orthoesters are used 100 . Korte and
Storiko et al. 101 reported and claimed C-4 acylated product by boiling 3-phenylisoxazol-
5(4H)-one with acetic anhydride in presence of sodium acetate. The above mentioned
methods were not fruitful to synthesize C-4 acylated isoxazolones as reported by Prager et
al. 102 and Reddy et al. 103 .
99 Pavithran, R.; Reddy, M. L. P. Radiochim. Acta 2004, 92, 31-38.
100 P. Rabe, Ber. Dtsch. Chem. Ges., 1897, 30, 1614.
101 F. Korte and K. Storiko, Ber. Dtsch. Chem. Ges., 1961, 94, 1956.
102 R. H. Prager, J. A. Smith, B. Weber and C. M. Williams, J. Chem. Soc., Perkin Trans. 1, 1997,
2659.
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