Lewis Acid-Promoted Cascade Reactions of Cyclopropenes: A Unified Approach to Stereoselective Synthesis of Cyclic Ethers and Oxaspirolactones

Lewis acid-promoted 5/6-exo trig hydroalkoxylation/reduction cascade of ω-hydroxy cyclopropenes gave expeditious, stereoselective access to THF/THP derivatives. Monoester substituted ω-hydroxy cyclopropenes on treatment with catalytic Bi(OTf)3 lead to [5,5]/[6,5] oxaspirocyclic lactones. This unified strategy relies on generation of transient donor-acceptor (D-A) cyclopropanes from ω-hydroxy cyclopropene precursors. This approach allows for the sequential addition of two nucleophiles in a 'one pot' process for the synthesis of THP derivatives. The utility of this methodology is demonstrated in the stereoselective synthesis of a homologue of (±)-civet.