Synthesis of 3-Acyl-isoxazoles and Δ<sup>2</sup>-Isoxazolines from Methyl Ketones, Alkynes or Alkenes, and <i>tert</i>-Butyl Nitrite via a Csp<sup>3</sup>–H Radical Functionalization/Cycloaddition Cascade
A novel metal-free tandem Csp3–H bond functionalization of ketones and 1,3-dipolar cycloaddition has been developed. An efficient approach to a variety of oxazole and isoxazoline derivatives is demonstrated using the 1,3-dipolar cycloaddition of alkynes and alkenes to nitrile oxides generated by reactions of methylketones with tert-butyl nitrite. This new protocol provides access to a variety of isoxazolines
Electrochemical and yeast-catalysed ring-opening of isoxazoles in the synthesis of analogues of the herbicide Grasp ®
作者:Christopher J. Easton、Graham A. Heath、C. Merrîcc M. Hughes、Connie K. Y. Lee、G. Paul Savage、Gregory W. Simpson、Edward R. T. Tiekink、George J. Vuckovic、Richard D. Webster
DOI:10.1039/b008081k
日期:——
Isoxazoles substituted with an electron-withdrawing group at the 4-position undergo electrochemical and yeast-catalysed N–O bond cleavage. The electrolysis is much more efficient and, with acyl- and alkoxycarbonyl-substituted isoxazoles, it affords the enolised dicarbonylimine functionality characteristic of the herbicide Grasp®. Regioisomeric 4- and 5-substituted isoxazoles are accessible through nitrile oxide cycloaddition chemistry, using halogen as a steric auxiliary to control the regiochemistry of reaction. Crystal data for compounds 11 and 19b are presented.