Titanium-mediated synthesis of primary cyclopropylamines from nitriles and Grignard reagents

This account presents studies on the development of a new method for the preparation of primary cyclopropylamines. The established procedure is simple and the reaction appears to be quite general. A wide range of nitrites and organomagnesium reagents can react to afford diversely substituted cyclopropylamines. Furthermore, bicyclic cyclopropylamines can be obtained via an intramolecular coupling from unsaturated nitrites. The reaction allows an easy preparation of 1-aminocyclopropanecarboxylic acids and 1-azaspirocyclic compounds bearing a cyclopropane ring. The reaction can also be applied to the preparation of polyfunctional and more complex organic molecules as exemplified with the synthesis of carbohydrates bearing aminocyclopropyl moieties and spirocyclopropyl pyrrolidines. During study of the title reaction, an unusual [4+1] cycloaddition reaction to afford cyclopentenylamines or cyclopentenones has been discovered and is described.