Asymmetric [3 + 2] Cycloaddition of 2,2′-Diester Aziridines To Synthesize Pyrrolidine Derivatives

A highly
diastereo- and enantioselective [3 + 2] cycloaddition
of 2,2′-diester aziridines with 3,4-dihydropyran derivatives
and acyclic enol ethers has been established. Various optically active
octahydropyrano­[2,3-c]­pyrrole and 3-methoxypyrrolidine
derivatives were generated in moderate to high yields (up to 94%)
and good stereoselectivities (>19:1 dr, up to 95.5:4.5 er). The
methodology
was also applied in the highly diastereoselective synthesis of d-galactal derivatives. The absolute configuration of the octahydropyrano­[2,3-c]­pyrroles showed that the reactions using 3,4-dihydropyran
and 6-alkyl-substituted ones as substrates gave reversed diastereoselection
in the final cyclization step.