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Iodocyclopropanes : Stereocontrolled preparation and uses in organic synthesis

University of British Columbia

The thesis is divided into three sections. Section 1 describes the stereoselective preparation of 2- and 3-iodo-2-alken-l-ols by a variety of methods and the cyclopropanation of these alkenyl iodides using the Wittig-Furukawa zinc reagent, (ClCH₂)₂Zn, derived from ClCH₂I and Et₂Zn. Cyclopropanation employing this reagent in ClCH₂CH₂Cl following the procedure of Denmark afforded highly functionalized iodocyclopropanes in good to excellent yields (13 examples). The method represents a novel preparation of functionalized iodocyclopropanes. For example, reaction of 26a with (ClCH₂)₂Zn in ClCH₂CH₂Cl resulted in smooth conversion to 60a in 87% yield. Two applications of iodocyclopropane chemistry to organic synthesis are described in Sections 2 and 3. The first application is the stereospecific synthesis of substituted cis- and trans-1,2-divinylcyclopropanes (7 examples) and 1-phenyl-2-vinylcyclopropanes (2 examples), in which the key step is the Pd(0)-catalyzed cross-coupling reaction of a vinylcyclopropylzinc chloride, derived from the corresponding vinyl iodocyclopropane, with an iodo alkene or iodobenzene. For example, treatment of iodocyclopropane 116b with 2.05 equivalents of BuLi, followed by metathesis of the resulting lithiocyclopropane with 1.5 equivalents of ZnCl₂ , provided the requisite cyclopropylzinc chloride. Coupling of the cyclopropylzinc chloride with iodo alkene 123 in the presence of Pd(PPh₃)₄ gave cis-1,2-divinylcyclopropane 152 in 54% yield. The second application of iodocyclopropane chemistry is the synthesis of spiro[2.4]heptanes via BuLi-mediated cyclization of substituted cis-1-(4-alkynyl)-2- hydroxymethyl-1-iodocyclopropanes (4 examples). For example, treatment of the iodocyclopropane 225 with 2.2 equivalents of BuLi provided the corresponding cyclopropyUithium intermediate, which subsequendy underwent 5-exo-dig cyclization to afford, on workup, the spiro[2.4]heptane 231 in 79% yield.

Thesis/Dissertation

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2009-03-20

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http://hdl.handle.net/2429/6296

Chemistry

University of British Columbia

UBCV

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