Electrochemical and yeast-catalysed ring-opening of isoxazoles in the synthesis of analogues of the herbicide Grasp
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.
Reversal of regiochemistry in the synthesis of isoxazoles by nitrile oxide cycloadditions
The isoxazolines 2a, 2b and 8 obtained from nitrile oxide cycloadditions to cyclohex-2-enone 1a and its analogues 1b and 7 reacted with nickel peroxide to give the isoxazoles 3a, 3b, and 9. In contrast, the correponding 2-bromocyclohex-2-enones 4a, 4b and
Easton,Easton, Christopher J.,Hughes,Merricc Hughes,Tiekink,Tiekink, Edward R. T.,Lubin,Lubin, Carolyn E.,Savage,Paul Savage,Simpson,Simpson, Gregory W.
p. 3589 - 3592
(2007/10/02)
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