Stereoselectivities, regioselectivities and yields for cyclopropanation reactions of diisopropyl diazomethylphosphonate (DAMP) with styrene derivatives, catalysed by ruthenium porphyrins, are reported and compared with those observed for cyclopropanation reactions catalysed by other metalloporphyrins. Linear correlations are observed when the rates for competitive cyclopropanation and ratio of the stereoisomers obtained are plotted against Hammet constants of various ring-substituted groups on styrene. Isomeric distribution for the cyclopropanation of 1,3-pentadiene with diisopropyl diazomethylphosphonate is reported. Competition studies between cyclopropanation and diazo insertion into heteroatom-hydrogen bonds and also between cyclopropanation and sigmatropic reaction are reported. A first example of asymmetric cyclopropanation with a chiral catalyst is also described. (C) 2003 Elsevier Science B.V. All rights reserved.