<i>cis</i>-2,3-Disubstituted Cyclopropane 1,1-Diesters in [3 + 2] Annulations with Aldehydes: Highly Diastereoselective Construction of Densely Substituted Tetrahydrofurans

A series of <i>cis</i>-2,3-disubstituted cyclopropane 1,1-diesters were examined in the AlCl<sub>3</sub>-promoted [3 + 2]-annulations with aldehydes. In this reaction, these <i>cis</i>-cyclopropanes displayed reactivities starkly different from their <i>trans</i> counterparts in terms of the high chemical yields (up to 98%) and provided the desired annulation products with excellent diastereomeric purity. This protocol provides a facile and highly stereoselective way to construct synthetically useful pentasubstituted tetrahydrofurans not easily accessible using other methods.