Abstract
A variety of 4-trifluoromethylquinolines bearing an aryl (or cyclopropyl, tert -butyl, trimethylsilyl) group at C-2 and a nitro group at ring position 6, 7 or 8 have been prepared in good to high yields from 3-substituted 1-(trifluoromethyl)prop-2-yne 1-iminium triflate salts and o -, m - or p -nitroaniline. These reactions include an aza-Michael reaction at room temperature followed by an intramolecular electrophilic aromatic substitution step, which requires additional thermal activation in most cases. In contrast, the conjugate addition of 2,4-dinitroanilines at the acetylenic iminium ions proceeds much more slowly and some of the adducts can be converted thermally into 2-(2,4-dinitrophenyl)-5-trifluoromethylpyrroles. Analogously, 2-(4-pyridyl)-5-trifluoromethylpyrroles were obtained from 3-aryl-1-(trifluoromethyl)propyniminium salts and 4-aminopyridinium triflate. A novel variation of the Truce–Smiles rearrangement is probably involved in the formation of these pyrroles.
Key words iminium salts - pyrroles - quinolines - fluoroorganic compounds - trifluoromethylated building blocks
