The Kulinkovich Cyclopropanation of Carboxylic Acid Derivatives

Cyclopropanes are characterized by high ring-strain energy and have been employed as useful building blocks in organic synthesis. The incorporation of a heteroatom donor substituent such as OH, OR, NR2, or SR on the ring imparts enhanced reactivity. Hydroxycyclopropanes (cyclopropanols) in particular have been thoroughly studied due to their facile ring cleavage. Among several known methods, a new method for preparation of cyclopropanols involves dialkoxytitanacyclopropane-mediated cyclopropanation (the Kulinkovich cyclopropanation) of esters with Grignard reagent in the presence of titanium isopropoxide. The striking feature of this method is the facile formation of a three-membered ring from a simple Grignard reagent which acts as a 1,2-dicarbanion equivalent through a pivotal dialkoxytitana-cycloproapne intermediate. These reactions benefit from the availability of inexpensive reagents, ease of operation, and high selectivity for cis-dialkylcyclopropanols. This cyclopropanation reaction has since been extended to other carboxylic derivatives to provide convenient access to several heteroatom-substituted cyclopropanes. The objective of this chapter is to provide an updated, comprehensive coverage of the literature on the Kulinkovich cyclopropanation reaction and related processes. Key mechanistic issues are summarized. Keywords: Kulinkovich cyclopropanation; Carboxylic acid derivatives; Grignard reagents; Titanium alkoxides; Cyclopropanol; Carbonyl compounds; Mechanisms; Esters; Aminocyclopropanes; Imides; Experimental procedures; Comparison of methods