Some Aspects of the Reactivity of RCu/BF3 Reagents towards the Ether Linkage

Organocopper reagents associated with a strong Lewis acid such as BF₃ react with the C--O single bond of orthoesters, acetals and epoxides. The diastereoselective cleavage of chiral acetals opens a new way of obtaining chiral secondary alcohols or chiral β -substituted aldehydes. A partial synthesis of the pheromone of the California red scale uses this approach. The opening of hindered epoxides is also very efficient with R₂CuLi/BF₃ reagents. Thus reaction with epoxy-silane gives rise to conjugated dienes as illustrated with the synthesis of the pheromones of Lobesia botrana and of Bombyx mori. Cyclohexene oxide reacts in the same way with R₄AlLi/BF₃ and the dienyl substituted cyclohexanols, thus obtained, can be used in highly stereoselective intramolecular Diels--Alder reactions.