Synthesis of Borylcyclopropanes by Chromium-Promoted Cyclopropanation of Unactivated Alkenes

The combination of diiodomethylboronate ester, CrCl2 with TMEDA promoted borylcyclopropanation of unactivated alkenes under mild conditions. Compared with the typical Simmons–Smith cyclopropanation, the current protocol offers the following advantages: (1) the reaction proceeds stereoselectively with disubstituted alkenes even without hydroxy or alkoxy groups; (2) both electron-rich and electron-deficient alkenes can be applicable; and (3) the reaction does not require potentially flammable alkylzinc. These unique reactivity features result from the steric and electronic nature of the gem-dichromiomethane intermediates.