Iron-catalyzed cyclopropanation in 6 M KOH with in situ generation of diazomethane.

Diazomethane is a common and versatile reagent in organic synthesis whose broader use is generally impeded by its explosiveness and toxicity. Here we report that a simple iron porphyrin complex catalyzes the cyclopropanation of styrenes, enynes, and dienes under the demanding conditions [aqueous 6 molar potassium hydroxide (KOH) solution, open to air] necessary for the in situ generation of diazomethane from a water-soluble diazald derivative. A biphasic reaction medium arising from the immiscibility of the olefin substrates with water appears essential to the overall efficiency of the process. The work we describe highlights an approach to catalysis with untoward reactive intermediates, in which the conditions for their generation under operationally safe regimes dictate catalyst selection.