Switchable reactions of cyclopropanes with enol silyl ethers. Controllable synthesis of cyclopentanes and 1,6-dicarbonyl compounds

(Chemical Equation Presented) Cu(SbF₆)₂-catalyzed reaction of 2-substituted cyclopropane-1,1-dicarboxylates 1 with enol silyl ethers 2 can be readily controlled: the reaction undergoes a cycloaddition to provide substituted cyclopentane derivatives 3 in excellent yields with high diastereoselectivities in the presence of complex 8/Cu(II); however, the same substrates afford acyclic 1,6-dicarbonyl products 4 via a cycloaddition-ring- opening reaction in up to 92% yield in the absence of ligand 8. The mechanism for the ligand-switchable reactions was investigated by both control experiments and ¹H NMR studies. The substrate scope and limitation of the tunable transformation were also examined.