ABSTRACT
An efficient non-aldol convergent synthesis of the C14-C25 polyketide fragment of bafilomycin A(1) was completed in 16% overall yield and 8 steps in its longest linear sequence. This synthesis highlights the formation of the key fragments using a three-step sequence of epoxide cleavage, alkyne reduction, and epoxidation developed in our laboratory; starting from suitably protected enantiomeric epoxides of trans-2,3-epoxybutanol. This chemistry represents a quick asymmetric and diastereoselective construction of the polyketide chain of bafilomycin A(1), in which every stereogenic center was constructed using solely epoxide chemistry.
ABSTRACT
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.
