Preparation of enantioenriched γ-substituted lactones via asymmetric transfer hydrogenation of β-azidocyclopropane carboxylates using the Ru-TsDPEN complex.

The asymmetric transfer hydrogenation of racemic β-azidocyclopropane carboxylates has been explored. Ru-TsDPEN B is found to be a good catalyst for the formation of enantioenriched γ-lactones through a four-step sequence of azide reduction/cyclopropane ring cleavage/ketone transfer hydrogenation/lactonization, and the enantiomeric excess of the lactones was up to 94%.