Methods for catalyzing CH insertion reactions using heme enzymes are described. The present disclosure provides a method for producing a CH insertion product comprising providing an substrate having an sp.sup.3-hybridized CH bond, a carbene precursor such as a diazo reagent, and a heme enzyme, and admixing the components in a reaction for a time sufficient to produce the CH insertion product. Heme enzyme variants useful for carrying out in vivo and in vitro CH insertion reactions, as well as expression vectors and host cells expressing the heme enzymes, are also described.