Iron(III)/Copper(II)-Cocatalyzed Cycloaddition/[3,3]-Rearrangement/N-O Bond Cleavage To Prepare Polysubstituted Pyrrolizines from N-Vinyl-α,β-Unsaturated Nitrones and Activated Alkynes.

An efficient one-pot synthesis of polysubstituted pyrrolizines from N-vinyl- α,β-unsaturated nitrones and activated alkynes through iron(III)/copper(II)-cocatalyzed [3 + 2] cycloaddition/[3,3]-rearrangement and sequential N-O bond cleavage was developed. The reaction first underwent [3 + 2] cycloaddition and [3,3]-rearrangement to afford nine-membered N-heterocycles, and then a controlled N-O bond cleavage of nine-membered rings by iron(III)/copper(II) cocatalysts delivered pyrrolizine scaffolds. A kinetic resolution of nine-membered ring compounds was achieved for the first time by using copper(II) acetate combined with a chiral PyBox ligand.