Stereoselective Insertion of Cyclopropenes into Mg–Mg Bonds

The reaction of cyclopropenes with compounds containing Mg–Mg bonds is reported. 1,2-Dimagnesiation occurs exclusively by syn-addition to the least hindered face of the alkene forming a single diastereomeric product. DFT calculations support a concerted and stereoselective mechanism. These findings shed new light on the stereochemistry of reactions involving magnesium reagents.