Divergent access to N-hydroxypyrroles and isoxazoles via the gold(i)- or Brønsted acid-catalysed regioselective cyclization of N-(2-trifluoromethyl-3-alkynyl) oximes

Qin Zeng; Li Zhang; Yuanjing Xiao; Junliang Zhang

doi:10.1039/c7ob03107f

Divergent access to N-hydroxypyrroles and isoxazoles via the gold(i)- or Brønsted acid-catalysed regioselective cyclization of N-(2-trifluoromethyl-3-alkynyl) oximes

Org Biomol Chem. 2018 Feb 21;16(8):1375-1380. doi: 10.1039/c7ob03107f.

Authors

Qin Zeng¹, Li Zhang, Yuanjing Xiao, Junliang Zhang

Affiliation

¹ Department of Chemistry, School of Chemistry and Molecular Engineering, East China Normal University, 500. Dongchuan Road, Shanghai, 200062, P. R. China. yjxiao@chem.ecnu.edu.cn.

PMID: 29411001
DOI: 10.1039/c7ob03107f

Abstract

The divergent regioselective cyclization of N-(2-trifluoromethyl-3-alkynyl) oximes by a suitable choice of a gold(i) or a Brønsted acid catalyst, leading to 4-trifluoromethyl-N-hydroxypyrroles or 4-trifluoromethyl-5-alkylisoxazoles was developed. In order to avoid the tedious separation of unstable N-(2-trifluoromethyl-3-alkynyl) oximes, an easy two-step, one-pot synthesis of 4-trifluoromethyl-5-alkylisoxazoles was realized via the sequential oxidation of the corresponding hydroxylamines and subsequent treatment with the reductant, sodium thiosulfate (Na₂S₂O₃)_. This two-step, one-pot procedure is a complementary method for the synthesis of 4-trifluoromethyl-5-alkylisoxazole from those unstable N-(2-trifluoromethyl-3-alkynyl) oximes.