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A remarkably simple method for the synthesis of di- and trisubstituted functionalised oxazoles under metal- and catalyst-free conditions is described. An iterative bromination and debromination of N-acylated amino acid derivatives with NBS as the sole reagent cleanly led to various substituted oxazoles.

A new cycloisomerization strategy for the synthesis of coumarins and quinolinones is described. The addition of ethoxyacetylide to 2-hydroxyacetophenones directly resulted in 4-substituted coumarins by 6-endo-dig cycloisomerisation of the intermediate 3-ethoxy-1-(2-hydroxyphenyl)-2-propyn-1-ols. Under similar conditions, 2-aminoacetophenone produced 2-ethoxyquinoline, a masked quinolinone, which was converted into the quinolinone by acid treatment. N-Protected intermediate 8 was isolated and converted into the quinolinone [with In(OTf)3 or H2SO4] or the 3-iodo-2-quinolinone (with I2 and H+).

1-n-Butyl-3-methylimidazolium chloroaluminate [bmim]Cl·AlCl3 (N = 0.56−0.67) ionic liquid has been employed as an alternative reaction medium to conventional acid catalysts for Prins cyclizations, to produce 4-chlorotetrahydropyran derivatives in excellent yields and in short reaction times. The ionic liquid plays a dual role as both catalyst and solvent, providing a rapid and efficient route to the synthesis of chlorotetrahydropyrans. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)