text: Methods for the stereoselective synthesis of cyclopropanes from diazocarbonyl compounds and olefins have relied on either the use of pre-formed chiral rhodium catalysts or chiral auxiliaries on the diazocarbonyl compound. For example, Rh[S-DOSP] is a highly effective catalyst for the enantioselective cyclopropanation of alkenes.
  Chiral auxiliaries derived from readily available chiral alcohols (such as pantolactone) may be used for diastereoselective cyclopropanations with diazo esters.