Highly regioselective copper-catalyzed cis- and trans-1-propenyl Grignard cleavage of hindered epoxides. application in propionate synthesis.

Hindered protected and unprotected epoxy alcohols were regioselectively cleaved using copper-catalyzed cis- and trans-1-propenylmagnesium bromide. The reaction exhibited good yield and excellent regioselectivity in systems where organocuprates and organoalanes failed. The cis Grignard reagent displayed no double-bond isomerization, whereas the trans isomer showed partial trans-to-cis equilibration, which was minimized by controlling the reagent formation conditions. The reaction was shown to be highly useful for the elaboration of the C10-C15 Streptovaricin D ansa chain fragment.