A method for selective mono-N-alkylation of primary amines to produce secondary amines that are substantially free of overalkylated tertiary amines and quaternary ammonium salts, under mild reaction conditions without the necessity of protecting groups. Compounds of the class of secondary amines are produced by reacting an alkyl halide with an alkyl amine in anhydrous solvent, preferably dimethyl sulfoxide or N,N-dimethylformamide, in the presence of 0.1 to 3 molar equivalents of a cesium base. Optionally, the extent and selectivity of mono-N-alkylation is enhanced by addition to the reaction mixture of a powdered molecular sieve material for removal of water produced by the reaction, and/or tetrabutylammonium iodide to promote halide exchange. The invention permits selective and efficient mono-N-alkylation of a wide variety of substrates at 23Â° C.; does not cause racemization when used with enantiomerically-pure chiral substrates such as L-Î±-aminoesters; and is applied to solid phase synthesis whereby either the alkyl amine or alkyl halide is immobilized. The method is additionally used to produce polyamines, such as N-(2-(2-aminoethylthio)ethyl)ethylenediamine in 73% yield.
Jung, Kyung Woon, "Efficient synthesis of secondary amines by selective alkylation of primary amines" (2002). USF Patents. 794.
University of South Florida