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.