Cyclopropanation Mediated by Lithium Iodide of Electron-Deficient Alkenes with Activated Dibromomethylene Compounds

Abstract

Reactions of electron-deficient alkenes with dibromomethylene compounds activated by cyanide and ester groups were promoted by LiI to afford the corresponding cyclopropanes in high yields.

Key words

cyclopropanes - dibromides - cyanides - esters - stereoselective synthesis

References and Notes

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3

In the early stages (0.5 h) of the reaction in Et₂O, 3ab was obtained in 65% yield with a lower diastereoselectivity (dr = 68:32) suggesting that the present reaction is thermodynami-cally controlled.

7

One referee suggested that IBr is generated during the reaction. We tried to capture it with styrene in DMF. The reaction (Table  [¹] , entry 5) was carried out in the presence of styrene (1 equiv), with the result that 3ab was reproducibly obtained with a small amount of 1-bromo-2-iodo-1-phenyl-ethane (<13%).