Triaryl oxazoles

From Table 1, below, no signs of thermal decomposition were observed below 400 °C for nitrile and sulfonyl substituted di-and triaryl oxazoles. Nitro compounds, in contrast, exhibited marked thermal decomposition exotherms with decomposition onset temperatures of 360-365 °C, conditions only marginally compatible with polyimide curing conditions. Nitro aromatics are also oxidants which may lead to long-term stability problems. As a result of these experiments nitrile and sulfonyl substituted diaryl oxazoles were selected for polymer doping studies. 

Related Reagents. (5)-2-(2,6-dimethoxyphenyl)oxazole hexamethylphosphoric triamide (5)-BINAP (+ )-DIOP trialkyl phosphines triaryl phosphines etc. 

Multiple arylations of oxazole was demonstrated with a paUa-dium/phenanthroline catalyst. Electron-deficient aryl iodides tended to provide the triarylated product, while more rich substrates furnished a mixture of products (eq 26). 

These conditions were utilized to perform a double arylation of oxazole and (V-methylimidazole at the C2 and C5 positions (eq 22). This protocol prevented the formation of the C2 4,5-triarylated heterocycles, as observed with Pd(phen)2(PFg)2. ... 

Figure 4. Synthesis of Donor-Acceptor Triaryl-and Diaryl-Oxazoles.

UV-Vis absorption spectra for triaryl nitrile-oxazole were determined in solvents of varying polarity. Dilute solutions (- 10-5 M) ofHPLC purified dyes were employed to eliminate concerns of spurious absorptions arising from dye-dye or dye-impurity interactions. Cell path lengths of 10.0 cm were used to maximize small absorption signals. Within experimental limits, no discernible charge-transfer absorptions were observed in any dye-solvent system in the region 600-900 nm. Minor solvatochromic effects were observed for absorption maxima. 

---