Three-Component Reaction of Sulfonamides with Acetylene and Amines

Abstract

N-(2-Phenyl-1-piperidin-1-ylethylidene)tosylamide was synthesized by oxidative coupling of arenesulfonamides, acetylenes, and secondary amines. The reaction of phenylacetylene or propargyl alcohol with triflamide and piperidine under the same conditions unexpectedly gave N-[(1E)-piperidin-1-ylmethylidene]triflamide TfN=CHNC₅H₁₀ as a result of cleavage of the triple bond in the alkyne. A similar reaction with benzoylacetylene gave (2E)-1-phenyl-3-piperidin-1-ylprop-2-en-1-one, while triflamide did not react. Adducts of a series of acetylenes with triflamide were obtained using triflamide sodium salt. Attempted synthesis of an N-triflyl-substituted analog of amidine 1 by the reaction of benzoylacetylene with triflamide and piperidine or morpholine in the presence of Cu(OTf)₂ and hydrogen peroxide as an oxidant unexpectedly gave 1-piperidin-1-yl- or 1-morpholin-1-ylmethanimine, respectively.