Part I. Development of an enantioselective cyclopropanation reagent. Part II. Studies on the addition of organometallic reagents to imine derivatives
Edwards, James Patrick
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https://hdl.handle.net/2142/19631
Description
Title
Part I. Development of an enantioselective cyclopropanation reagent. Part II. Studies on the addition of organometallic reagents to imine derivatives
Author(s)
Edwards, James Patrick
Issue Date
1991
Doctoral Committee Chair(s)
Denmark, Scott E.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Language
eng
Abstract
Efforts to develop an enantioselective zinc-based cyclopropanation reagent are described. Enantioselectivities of up to 24% e.e. were achieved using N-methylephedrine as a chiral controller ligand for iodomethylzinc cyclopropanations of cinnamyl alcohol. Chiral bis-ether complexes of bis(iodomethyl)zinc were found to react sluggishly and without enantiocontrol, indicating that the use of chelating ligands dramatically attenuates the reactivity of iodomethylzinc species.
Extensive spectroscopic studies of halomethylzinc reagents are also reported. NMR spectroscopic studies demonstrated for the first time the formation of bis(iodomethyl)zinc and bis(chloromethyl)zinc from the reaction of diethylzinc with diiodomethane and chloroiodo-methane respectively. The conversion of bis(iodomethyl)zinc complexes to iodomethylzinc iodide complexes was also demonstrated. These latter species were determined to exist predominantly as bis(iodomethyl)zinc/zinc iodide species in acetone solution. The first X-ray crystallographic analysis of an iodomethylzinc compound is also described in detail.
A study of the addition of organocerium reagents to imine derivatives is also reported. The ratio of alkyllithium reagent to cerium(III) chloride used to generate the organocerium reagent was shown to have a dramatic effect on the yield of additions to N,N-dimethylhydrazones. Ratios of greater than 3:1 resulted in much lower yields using methyllithium as the limiting reagent, while lowering the ratio resulted in a small but measurable improvement in yield. Organocerium additions to chiral 2-substituted pyrrolidine hydrazones were also studied, and were shown to proceed with high levels of diastereocontrol without the need of coordinating appendages in the auxiliary side-chain, indicating that the diastereocontrol observed in additions to SAMP-hydrazones is not the result of chelation-control.
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