5- -2-alkyl-4-methyloxazoles

See Hydrogen peroxide 2-Amino-4-methyloxazole See related ALKYL HYDROPEROXIDES... 

The primary adducts (156) and (157) of oxazoles with alkenes and alkynes, respectively, are usually too unstable to be isolated. An exception is compound (158), obtained from 5-ethoxy-4-methyloxazole and 4,7-dihydro-l,3-dioxepin, which has been separated into its endo and exo components. If the dienophile is unsymmetrical the cycloaddition can take place in two senses. This is usually the case in the reactions of oxazoles with monosubstituted alkynes with alkenes on the other hand, regioselectivity is observed. Attempts to rationalize the orientation of the major adducts by the use of various MO indices, such as 7r-electron densities or localization energies and by Frontier MO theory (80KGS1255) have not been uniformly successful. A general rule for the reactions of alkyl- and alkoxy-substituted oxazoles is that in the adducts the more electronegative substituent R4 of the dienophile occupies the position shown in formula (156). The primary adducts undergo a spontaneous decomposition, whose outcome depends on the nature of the groups R and on whether alkenes or alkynes have been employed. 

Both 4- and 5-methyloxazoles are normal compounds rather like toluene, but if the alkyl group is at position 2 it is capable of undergoing a variety of addition and condensation reactions. 

In the case of lower alkyl amides the components are heated in a high-boiling inert solvent such as xylene or dimethylformamide.8788 Ethyl a-chloroacetoacetate reacts with benzamide at 180° to give a very poor yield of ethyl 2-phenyl-4-methyloxazole-5-carboxylate.27... 

---