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36.2.1.1.4.1 Variation 1: Titanium(IV)-Mediated Cyclopropanation of Esters

DOI: 10.1055/sos-SD-036-00360

Scott, P. J. H.; Steel, P. G.Science of Synthesis, (200836468.

A novel method for the synthesis of cyclopropanols was reported by Kulinkovich and this methodology, which now bears his name, has since found widespread application.[‌1‌,‌69‌‌82‌] In the original reaction, methyl esters are treated with Grignard reagents (3 equiv) in the presence of titanium(IV) isopropoxide (1 equiv) to give 1-substituted cyclopropanols 4 (Scheme 2).[‌83‌] The main limitation with this procedure is the need for a stoichiometric amount of the titanium reagent, and subsequent developments have led to a catalytic process in which cyclopropanols can be prepared using only 510mol% of titanium(IV) isopropoxide.[‌84‌] The reaction is thought to proceed through a diethyltitanium intermediate that is unstable and undergoes rapid β-hydride elimination to give a titanacyclopropane. This species then serves as a double alkylating agent, capable of converting esters into cyclopropanols.

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