Transition metal-catalyzed cyclopropanation of alkenes in water: catalyst efficiency and in situ generation of the diazo reagent

[reaction: see text] A cyclopropanation reaction involving ethyl diazoacetate and olefins proceeds with surprisingly high efficiency in aqueous media using Rh(II) carboxylates. Nishiyama's Ru(II) Py-box and Katsuki's Co(II) Salen complexes that allow for highly enantioselective cyclopropanations in organic solvents can also be applied to aqueous cyclopropanations with similar results. In situ generation of ethyl diazoacetate and cyclopropanation also proceeds efficiently. A chemoselective O-H insertion is also possible in water when hydrophobic catalysts and alcohols are used.