Synthetic applications of intermolecular cyclopropanation of carboxylic esters with dialkoxytitanacyclopropane reagents

The reaction of carboxylic esters with ethylmagnesium bromide in the presence of titanium(iv) isopropoxide, which leads to the formation of substituted cyclopropanols, was disclosed in the late 1980's. The key organometallic intermediates in this transformation are diisopropoxytitanacyclopropane species, which act as 1,2-dicarbanionic equivalents. The intermolecular titanium-mediated cyclopropanation of carboxylic esters and subsequent transformation of the three-membered ring provides a convenient and flexible approach to the construction of the carbon skeleton of organic molecules with ketone and other functionalities. Applications of this methodology to the synthesis of natural biologically active compounds and their analogues have been published over the last fifteen years and are summarized in the present review article. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).