Titanium-Mediated Cyclopropanation of Nitriles with Unsaturated Grignard Reagents: Application to the Synthesis of Constrained Lysine Derivatives

A comparative study of the titanium-mediated cyclopropanation of (benzyloxy)acetonitrile and Boc-protected cyanohydrin using unsaturated Grignard reagents (but-3-enyl- and pent-4-enylmagnesium bromides) is described. The best conditions to provide the cis and trans isomers of cyclopropylamines bearing unsaturation were identified and the alkene moiety was subjected to chemical modifications, as shown by the synthesis of orthogonally protected cis- and trans-2,3-methanolysine, cis-2,3-methanoornithine, and cis-2,3-methanohomolysine.