Efficient solid support catalyzed mono-aza-Michael addition reactions of piperazine

Abstract

We report new methods for the efficient mono-aza-Michael additions of piperazine to compounds with activated multiple carbon–carbon bond (functional derivatives of acrylic, propiolic, and acetylenedicarboxylic acid). This method is based on the reaction of piperazine-1-ium cation with alkenes or alkynes substituted by EWGs under catalysis by various metal ions supported on weakly acidic cation-exchanger resin. Starting piperazine-1-ium cation is generated in situ in methanol solution by mixing of piperazine and piperazine-1,4-diium dichloride in various ratios. It was found that solid support metal catalysis afforded target products in very good yields in shortened reaction times. A new method of N-monosubstituted piperazine derivative preparation is very beneficial, because until now no one has come up with the idea to use for protection of the one nitrogen atom of the piperazine its simple protonation. Computer modeling of behavior of piperazine depending on the pH was carried out and according to the results, we concluded that the protonation of the nitrogen atom is the simplest, most effective, and most elegant method of preventing unwanted formation of 1,4-disubstituted product. Assumption was fully confirmed by number of syntheses. The main advantages of our syntheses are great simplicity, one-pot performance, use of non-toxic solvents only, mild reaction conditions, no generation of waste, short time of reactions, and high yields.

Graphical abstract

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