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Dissertation Information for Kimberly J. Worsencroft

NAME:
- Kimberly J. Worsencroft

DEGREE:
- Ph.D.

DISCIPLINE:
- Chemistry

SCHOOL:
- Emory University (USA) (1999)

ADVISORS:
- Albert Padwa

COMMITTEE MEMBERS:
- Frank E. McDonald
- David Goldsmith

MPACT Status: Fully Complete

Title: Cyclization studies using rhodium carbenoids of alpha-diazo amides: Synthesis of nitrogen-containing heterocycles

Abstract: "The rhodium (II)-catalyzed decomposition of [Special characters omitted.] -diazo carbonyl compounds containing an amido group in the [Special characters omitted.] -position and their subsequent cycloaddition behavior was examined in some detail. A series of substituted [Special characters omitted.] -diazo amides were synthesized and found to undergo a tandem cyclization-cycloaddition reaction via a push-pull carbonyl ylide intermediate in the presence of a rhodium (II) catalyst. Intramolecular capture of the transient ylide with an internally disposed [Special characters omitted.] -bond resulted in formation of complex nitrogen-containing heterocycles in a single step. The tandem cyclization-cycloaddition strategy was highlighted by application to the synthesis of the galanthan nucleus of the Amaryllidaceae alkaloids.

Reaction of related cyclopropanated substituted [Special characters omitted.] -diazo keto amides with rhodium (II) carboxylate catalysts resulted in cyclization on both the oxygen and nitrogen atoms of the amido group to produce five-membered carbonyl and ammonium ylides depending on the reaction conditions employed. In the absence of an external dipolarophile, ammonium ylides were the exclusive products formed. These ylides could not be isolated as they readily underwent sigmatropic rearrangement or fragmentation reactions. In the presence of typical dipolarophiles such as DMAD or N -phenylmaleimide, cycloaddition products derived from both push-pull carbonyl and ammonium ylides were obtained. The product distribution between these ylide intermediates was directly related to the rhodium catalyst used.

The utility of ammonium ylides was also tested for alkaloid synthesis. Ammonium ylides derived from rhodium (II)-catalyzed decomposition of appropriately substituted [Special characters omitted.] -diazo amides underwent a tandem ammonium ylide generation/Stevens rearrangement cascade to give structurally diverse polyheterocycles. The flexibility of this method was further demonstrated through the synthesis of the isoindolobenzazepine ring system contained in the Berberidaceae family and related alkaloids.

Density functional theory calculations were performed on a series of substituted dirhodium (II) tetraformate carbenoid complexes. These calculations have allowed us to make predictions about the importance of ligand groups on the rhodium metal and their potential in the ligand-directed chemoselectivity of rhodium carbenoid reactions. We were also able to map out a plausible catalytic pathway for rhodium (II) catalysts which provides a better understanding of reversible dipole formation. According to these results, ammonium ylides possessed a significantly greater thermodynamic stability than the isomeric carbonyl ylides."

MPACT Scores for Kimberly J. Worsencroft

A = 0
C = 0
A+C = 0
T = 0
G = 0
W = 0
TD = 0
TA = 0
calculated 2008-04-13 14:13:29

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