4-Alkoxycarbonyl- and Aminocarbonyl-Substituted Isoxazoles as Masked Acrylates and Acrylamides in the Asymmetric Synthesis of Δ<sup>2</sup>-Isoxazolines
作者:Connie K. Y. Lee、Anthony J. Herlt、Gregory W. Simpson、Anthony C. Willis、Christopher J. Easton
DOI:10.1021/jo0602569
日期:2006.4.1
treatment with sodium borohydride and sodium trifluoroacetoxyborohydride, respectively. They are also alkylated at C5 through sonication with secondary and tertiary alkyl iodides in the presence of zinc dust and copper(I) iodide. These reactions are analogous to those observed with acrylates and acrylamides. The behavior is characteristic of the 4-substituted isoxazoles but not the 5-substituted regioisomers
Substituent effects in isoxazoles: identification of 4-substituted isoxazoles as Michael acceptors
作者:Connie K. Y. Lee、Christopher J. Easton、Mariana Gebara-Coghlan、Leo Radom、Anthony P. Scott、Gregory W. Simpson、Anthony C. Willis
DOI:10.1039/b207808b
日期:2002.12.6
Crystallographic and theoretical studies have been used to investigate substituent effects, which are manifest in electrochemical and yeast-catalysed reactions of 4- and 5-acyl-, alkoxycarbonyl-, cyano- and phenyl-substituted isoxazoles. The results show that isoxazoles substituted at the 4-position with π-electron-withdrawing substituents have enhanced C4–C5 bond polarity and are structurally similar to Michael acceptors. As a consequence there is elongation and weakening of their N–O bonds. By contrast, their 5-substituted regioisomers and isoxazoles substituted at C4 with conjugating, but not π-electron-withdrawing, substituents have diminished C4–C5 bond polarity. This results in the selective electrochemical and yeast-catalysed reduction of 4-substituted isoxazoles, as well as their hydrogenolytic ring cleavage and conjugate reduction with sodium borohydride.