Catalytic Enantioselective Synthesis of Tetrahydrofurans: A Dynamic Kinetic Asymmetric [3 + 2] Cycloaddition of Racemic Cyclopropanes and Aldehydes

A highly diastereoselective dynamic kinetic asymmetric transformation of racemic 1,1-cyclopropane diesters to prepare enantioenriched tetrahydrofuran (THF) derivatives has been developed. Asymmetric [3 + 2] cycloaddition of activated donor-acceptor (D-A) cyclopropanes and aldehydes catalyzed by ((t)Bu-pybox)MgI(2) gives THF products in good to excellent yields (48-92%) as single diastereomers with er's up to 97:3. Aryl, cinnamyl, and aliphatic aldehydes are competent dipolarophiles for this transformation.