The [(salen)CrCl + LB] catalyst system was found to be a highly active catalyst system for the [aziridine + CO₂] coupling reaction, and exhibited a marked preference for the formation of 5-substituted oxazolidinone product, especially in the absence of cocatalyst. The activity of this catalyst system is optimized by modifying the cocatalyst and tuning the reaction conditions to facilitate the conversion of a wide variety of substituted aziridines into oxazolidinones under mild reaction conditions. An investigation of the [(salen)CrCl + LB]-catalyzed [aziridine + CO₂] coupling reaction was very instructive. A Hammett plot of aziridine substituents and a series of DFT ground-state calculations both intimated a transition state having cationic character. However, several experiments showed convincingly that a carbocation does not exist during the course of the catalyzed [aziridine + CO₂] coupling reaction. Opposite-face ligand attachment was studied as well, both using experiment and DFT calculations, and give a rationale for the observed selectivity differences between many of the Lewis bases used as cocatalysts. Finally, a transition state calculation has shown the energetic difference between the two product regioisomers. Expanding the (salen)CrCl-catalyzed [aziridine + CO₂] coupling reaction to include the [aziridine + isocyanate] coupling has opened this methodology to produce a series of imidazolidinones. Optimization of the [aziridine + isocyanate] coupling reaction has shown that, in contrast to the [aziridine + CO₂] and [epoxide + CO₂] coupling, a Lewis basic cocatalyst does not improve either the rate or the selectivity of the ring-expansion. Rather, it hinders the reaction rate. Further optimization of the reaction conditions have produced a coupling methodology that is amenable to a wide range of aziridines and isocyanates. Finally, the conversion of aziridines and organic carbonyls to form oxazolidines were attempted. While the (salen)CrCl catalyst was not capable of facilitating this transformation, another Lewis acid, Sc(OTf)₃ was active in this role. Upon an investigations of reaction parameters including ligand additive, temperature, concentration, and substrate effects, conditions useful for the conversion of both aldehydes and ketones to <em>N</em>-tosyl oxazolidines were formed.

Last modified

• 06/05/2018

Creator

• Aaron W Miller

DOI

• https://doi.org/10.21985/N28T4S

Subject

• Chemistry

Keyword

• Chemistry
• Organic

Date created

• 2007-05-11

Resource type

• Dissertation

Rights statement

• In Copyright