A method of preparing a cyclopropane ring-bearing compound of the formula I in which R1 and R2 are independently selected from C1-C10 alkyl, optionally substituted, or R1 and R2, together with the bonds linking them to the cyclopropane ring, form a monocyclic or bicyclic ring system, which may comprise at least one hetero-atom, comprising the reaction of a compound of formula II R1—CH═CH—R2  II in which R1 and R2 have the significances hereinabove defined, with a compound of formula III X—CH2—Y  III in which X is a nucleofuge selected from halides and pseudohalides and Y is an electrofuge selected from boranes and borates, in the presence of a metal catalyst complex selected from those useful for catalytic cyclopropanation and those useful for catalyzing Heck coupling. The method provides a particularly easy and non-hazardous method of cyclopropanation.