Preparation of carbocycles via cycloisomerization of unsaturated organolithiums: Part A. Lithium-halogen exchange-initiated transformations Part B. Optimization of chromatographic separations

Date of Completion

January 2009

Keywords

Chemistry, Organic

Degree

Ph.D.

Abstract

The preparation of five- and six-membered carbocycles via cyclization of organolithiums tethered to remote π–bonds has been investigated. The isomerization of 6-heptenyllithium to (cyclohexylmethyl)lithium is compromised by a 1,5-proton transfer to give an allylic anion. Similar behavior was observed in an anionic cascade involving three sequential 5-exo-trig cyclizations designed to deliver the strained stellane skeleton ( i.e., tricyclo[3.3.0.03,7]octane). The behavior of acyllithiums generated by reaction of organolithiums with carbon monoxide has been investigated, with little success, as a route to monocyclic ketone products. ^ The lithium-iodine exchange-initiated fragmentation of 4-substituted-2-iodomethy1-1,3-dioxanes proceeds in a regioselective manner via preferential cleavage of the less sterically congested C(2)–O bond. The selectivity of these Boord fragmentations is attributable to a strong steric component of the complex-induced proximity effect. ^ A tool that assists in the method development of flash chromatographic separations is described. Utilizing the crude sample mass and thin-layer data, a spreadsheet calculates a mass of silica gel to be loaded into a column and an optimal fraction size for that mass. The spreadsheet accurately estimates the retention volume and band volume of analytes, as well as the respective fractions containing each analyte. The utility calculates the resolution between adjacent peaks and allows the comparison of multiple solvent systems for their ability to separate analytes on a preparative scale. A complementary spreadsheet was developed to scale flash chromatographic separations. ^ Rapid on-site identification of volatile organic compounds (VOCs) in ambient air is an important first step in remediation efforts. A commercially available, portable GC/MS system has been modified and an analysis protocol has been developed for rapid (< 3 min) sampling and identification of VOCs typically found at contaminated sites at the low ppbv level. ^

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