General Conditions of Rearrangements

The Claiaen rearrangement in nitrogen heterocyclic systems has been carried out in many different solvents. The ease of allylic migration appears to vary considerably among the different systems. The solvent media commonly employed are diethylaniline, 1-methyl-naphthalene, and AjA-diethyl-m-toluidine (b.p., 231°). In other instances, where the allyl ethers are liquids, the rearrangement has also been effected without any solvent. Under these conditions, the results are not always the same as those observed with a solvent. 

The rearrangements could often be followed by the change in the ultraviolet absorption spectra (as in the case of the allyloxypyridine-1-oxides) or through quantitative analysis by paper chromatography of the product mixture (as in the case of the pyrimidine derivatives) or by gas liquid chromatography and infrared spectral analysis (as in the case of the quinoline derivatives). 

---