A novel Suzuki-type cross-coupling reaction of cyclopropylboronic esters with benzyl bromides

Abstract

The Suzuki-type coupling reaction of cyclopropylboronic acids (esters) with benzyl bromides readily takes place by using Ag₂O with KOH as the base. The reaction rate and the cross-coupling product yields of cyclopropylboronate esters of ethylene glycol or propane-1,3-diol were higher and better than those of cyclopropylboronic acids. However, the coupling reaction of the cyclopropylboronate esters of glycol with larger substituents was sluggish. The highly optically active benzyl-substituted cyclopropanes could be obtained by the coupling reactions of corresponding optically active cyclopropylboronate esters with benzyl bromides. A novel, ideal method for preparing stereo-defined benzyl-substituted cyclopropanes, especially optically active benzyl-substituted cyclopropanes, is described here.