Graduate Thesis Or Dissertation
 

Synthetic studies toward a total synthesis of paeoniflorigenin

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  • A new approach towards a total synthesis of paeoniflorigenin is discussed. The approach involves the application of regio- and stereoselective [2+2] photocycloaddition for the preparation of a key intermediate, cyclobutanone 86, and model studies on diiodosamarium (Sm12) mediated pinacol coupling of a diketone. Intermolecular [2+2] photocycloaddition of a,13unsaturated lactam 33 to ketene acetal 34 generated exclusively a head-to-tail and endo cyclobutanone derivative 35. Singlet oxygen oxidation generated butenolide 76, which is a precursor for preparation of photosubstrate 78. Intramolecular [2+2] photocycloaddition using a siloxane as temporary tether, a key step in this synthetic sequence, resulted in tricyclic siloxane intermediate 79. A stepwise oxidative cleavage of O-Si and C-Si bonds in 79 according to Tamao's procedure afforded cyclobutanol 85. Swern oxidation of 85 resulted in highly oxygenated cyclobutanone 86. Overall, a total of eleven steps from the commercial available 3-furaldehyde allowed us to prepare this highly functionalized intermediate 86. Diiodosamarium (SmI2) mediated pinacol coupling of diketone 92 formed a diastereomeric mixture of vicinal bis-tertiary diols 93a and 93b.
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Déclaration de droits
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