Three-Component Synthesis of Highly Substituted 2-Imidazolines

Significance

A copper-catalyzed, two-step, three-component synthesis of 2-imidazolines is described, starting from unsubstituted aziridines 1, terminal acetylenes 2 and sulfonyl azide 3. The copper-catalyzed formation of 4 is tolerant of a range of aryl substitution in 1, although reaction times are relatively long due to steric hindrance of the N-unsubstituted aziridine. Both aromatic and aliphatic acetylenes were shown to participate in the reaction. The use of either a highly electron-deficient aziridine (Ar¹ = 4-O₂NC₆H₄) or acetylene (R = 4-O₂NC₆H₄) as one of the coupling partners, however, gave no product. Isomerization of 4 to 2-imidazolines 5 was accomplished using NaI in acetone in moderate to good yield (H. Heine, H. Bender J. Org. Chem. 1960, 25, 461).