Stereoselective sulfonium ylide cyclopropanation is a useful transformation due to the presence of this moiety in numerous bioactive compounds. The procedures described to date involve long reaction times and variable stereoselectivity outcomes. We show here that performing these reactions under MW mediation gives good yields and selectivity after short reaction periods. The methodology is applied to different substrates including sterically hindered cyclopentenones, open chain unsaturated esters and pentalenones (Pauson-Khand products). From these latter substrates, highly connected cyclopropa[c]pentalenes were synthesized in good yields, including a precursor of natural product pentalenene.