Reactions of 1-Trifluoromethylprop-2-yne 1-Iminium Salts with Nitroanilines: Synthesis of 4-Trifluoromethylnitroquinolines and 1,2,3-Trisubstituted 5-Trifluoromethylpyrroles

Abstract

A variety of 4-CF3-quinolines 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-CF3-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-CF3-pyrroles. Analogously, 2-(4-pyridyl)-5-CF3-pyrroles were obtained from 3-aryl-1-CF3-propyne iminium salts and 4-aminopyridinium triflate. A novel variation of the Truce-Smiles rearrangement is probably involved in the formation of these pyrroles.

Recent advances in the synthesis of trifluoromethyl-containing heterocyclic compounds via trifluoromethyl building blocks

“…An effective approach to synthesizing 4-trifluoromethylnitroquinolines and 1,2,3-trisubstituted 5-trifluoromethylpyrroles from 1-trifluoromethylprop-2-yne 1-iminium salts and nitroanilines was developed by Maas et al 93 in 2021 (Scheme 65). A number of different 4-trifluoromethylquinolines with various functional groups at the C-2 position and extra nitro groups at the C6, C7, or C8 positions were prepared in satisfactory to excellent yields from 3-substituted 1-(trifluoromethyl)prop-2-yne 1-iminium triflate salts and mononitroanilines.…”