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.
An efficient non-aldol convergent synthesis of the C14–C25 polyketide fragment of bafilomycin A1 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 A1, in which every stereogenic center was constructed using solely epoxide chemistry.
Oxirane derivatives R 0030Highly Regioselective Copper-Catalyzed cis-and trans-1-Propenyl Grignard Cleavage of Hindered Epoxides. Application in Propionate Synthesis. -It is found that hindered epoxides can be cleaved with high regio-and stereoselectivity by CuI-mediated treatment with vinylic Grignard reagents. During reaction with trans-bromopropene/Mg competitive double bond isomerization takes place. -(RODRIGUEZ, D.; MULERO, M.; PRIETO*, J. A.; J. Org. Chem. 71 (2006) 15, 5826-5829; Dep. Chem., Univ. Puerto Rico, San Juan, PR 00931, P. R.; Eng.) -Jannicke 48-114
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.