A Copper-Catalyzed Method for the Facially Selective Addition of Grignard Reagents to Cyclopropenes

A Cu-catalyzed method for the addition of Grignard reagents to 1-alkyl-3-hydroxymethylcyclopropenes and their MOM ethers is described. The face of addition is syn relative to the hydroxymethyl and alkoxymethyl groups. Excellent diastereoselectivity is observed for a range of alkyl, alkenyl, and alkynylmagnesium halides. The addition reactions create chiral all-carbon quaternary centers, and the cyclopropylmetals that are generated can be reacted with electrophiles to produce highly functionalized cyclopropanes.