Part I. The first enantioselective synthesis of the chiral bisnaphthopyrone natural product nigerone and its enantiomer, ent-nigerone, has been achieved. The synthesis of nigerone highlights the asymmetric oxidative biaryl coupling with 1,5-diaza-cis-decalin copper complexes that was developed by the Kozlowski group. It was found that constrained 2-naphthols were necessary to produce the highly functionalized chiral 1,1'-binaphthols in high enantioselectivity. The key eight-step isomerization process to form the natural product proceeded with retention of the biaryl configuration. The axial configurations of bisisonigerone and nigerone were definitively established through a combination of circular dichroism (CD) measurements and quantum chemical CD calculations.*
Part II. Catalytic, enantioselective Claisen rearrangements have been studied. The first of the [3,3'] sigmatropic rearrangements utilized a bisamidinium catalyst, featuring a dual hydrogen-bonding array that can coordinate a singular oxygen atom on the Claisen substrate. It was found that the dual hydrogen donor was key, as acceleration of the Claisen rearrangement was far greater than with using twice as much of a mono hydrogen bond donor.*
Next, the first catalytic, enantioselective Meerwein-Eschenmoser Claisen rearrangement has been developed. Both copper(II) and palladium(II) catalysts were employed. The reaction was optimized to afford the oxindole product bearing a quaternary stereocenter at C3 in high enantiomeric excess.*
*Please refer to dissertation for diagrams.
|Advisor:||Kozlowski, Marisa C.|
|School:||University of Pennsylvania|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-B 70/10, Dissertation Abstracts International|
|Keywords:||Claisen rearrangements, Hydrogen-based donors, Nigerone|
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