Enantio- and Diastereoselective Cyclopropanation of 1-Alkenylboronates: Synthesis of 1-Boryl-2,3-Disubstituted Cyclopropanes

A novel, highly enantio- and diastereoselective synthesis of 1-boryl-2,3-disubstituted cyclopropanes has been developed by means of the cyclopropanation of alkenylboronates with ethyl diazoacetate in the presence of catalytic amounts of a chiral copper(I) complex. The products can also be directly accessed from alkynes through an operationally simple, sequential hydroboration–cyclopropanation protocol. The resulting enantioenriched 1-boryl-2,3-disubstituted cyclopropanes are versatile synthetic intermediates that undergo further transformations at the carbon–boron bond.
We thank MINECO for financial support (CTQ2014-52769- C03-01-R and Juan de la Cierva fellow for J.C.) and Junta de Andaluc a (P12-FQM-1765). We also thank Riccardo Gava and Cristina Gonzalez for additional experiments and Francisco Molina for X-ray diffraction studies.