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1. Rearrangement of Vinyl Epoxides in Ionic Liquids

The goal of this project is to further define the scope and limitations of a new synthetic methodology that is based on the rearrangement of vinyl epoxides to the corresponding dihydrofurans using a catalyst system that also serves as an ionic liquid solvent. A simple example of this process is shown below.

Rearrangement of vinyl epoxides diagram

The tin component of the catalyst serves as a Lewis Acid that complexes to the epoxide oxygen and enhances its reactivity with nucleophiles. The phoshonium iodide acts as a source of the required iodide nucleophile as well as the solvent for the reaction. The use of an ionic liquid solvent obviates the need for volatile organic solvents and as such allows this methodology to be "green" and friendly to the environment.

To date in Dr. Godleski's research group, this method has been demonstrated for a variety of cyclic and acyclic vinyl epoxides. An example of which is shown below.

acyclic vinyl epoxides diagram

The research proposed for the summer internship will focus on the elucidation of the stereochemical aspects of this methodology. Specifically, if the vinyl epoxide has defined stereochemistry will this stereochemistry be translated to the dihydrofuran product. For example, will the trans, trans-stereochemistry of the diene monoepoxide shown below translate to the trans disposition of the methyl groups in the pictured dihydrofuran. A number of examples will be studied under varying reaction conditions to probe this question.

reaction diagram

Any stereospecificity associated with this methodology will greatly extend its utility in organic synthesis. Finally, the potential of introducing chirality into the furan product via an optically active phosphonium salt ionic liquid will be explored.

A student working on this project will get experience in synthetic organic and organometallic chemistry, the preparation, purification and spectrospcopic characterization of new materials, and the development of a new synthetic methodology.

2. Organosilvers as Precursors to Radicals

Organosilvers have a considerable propensity to undergo homolytic cleavage to produce a silver atom and the corresponding organic radical. We are exploring the organosilver species as a means for very mild and specific generation of organic radicals that could be utilized in chemically useful cyclization reactions. Radical mediated cyclization processes have been widely investigated and has been found to be a very important synthetic methodology.[1-5] Radical mediated cyclizations can be advantaged relative to ionic processes due to their chemoselectivity, better toleration of steric crowding, and mild reaction conditions.[1]

Organosilvers can be made via transmetallation from a variety of available organometal precursors including RMgX, RLi, R4Pb, R4Sn and RB(OH)2.[1] A typical example is shown below.

chemical compound reaction diagram

Our approach will be to initially prepare functionally simple systems to first prove the concept of organosilvers as radical precursors for cyclization reactions . We will then establish the comparative regio and stereochemical preferences for the organosilver mediated reactions. A fundamental question to be addressed in these studies is whether the organosilver species produces a true "free radical" or it produces a species with the silver still associated via a metal complex. The latter could clearly influence the reactivity and selectivity characteristics of these species.

reaction diagram

This methodology could be a significant addition to the existing organo-radical methodology and may provide valuable alternatives to previous methods, especially if the organic radical has metalloid character. In addition, the considerable driving force for homolysis possessed by organosilvers could make highly unstable radicals available that cannot be formed readily by other methods.

A student working on this project will get experience in synthetic organic and organometallic chemistry, the preparation, purification and spectrospcopic characterization of new materials, and the development of a new synthetic methodology.

[1] D.P. Curran, Synthesis, (1988), 417.
[2] D.P. Curran, Synthesis, (1988), 489.
[3] M. Julia, Accounts of Chemical Research, 4 (1971), 386.
[4] D.L. Boger, Isr. Jour. Chem., 37 (1997), 119.
[5] B. Geise, B. Kopping, T. Gobel, J. Dickhaut, G. Thoma, K.J. Gulicke, F. Trach, Org. Reactions, 48 (1996), 301.

Last Updated 9/14/18

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