1-Fluoroalkyl-prop-2-yne 1-imines and 1-iminium salts as building blocks: a new synthesis of α-(trifluoromethyl)pyrroles

Abstract 1-Fluoroalkyl-prop-2-yne 1-N,N-dimethyliminium triflate salts were obtained by N-methylation of alkynyl fluoroalkyl N-methylketimines. They represent a novel and, due to the activating effect of the fluoroalkyl group, highly reactive class of acetylenic iminium salts. Herein we describe the two-step conversion of the CF3-substituted iminium salts into 1,4-disubstituted α-CF3-pyrroles by Michael addition of triphenylphosphane and thermally induced cyclization of so-formed (3-aminoallenyl)phosphonium salts. While the mentioned alkynyl trifluoromethyl N-methyl-ketimines were obtained by copper-catalyzed cross-coupling of terminal alkynes and N-methyl-2,2,2-trifluoroacetimidoyl chloride, terminal alkynes and N-benzyl-2,2,2-trifluoroacetimidoyl chloride under the same reaction conditions furnished 2,3-disubstituted 5-CF3-pyrroles directly.