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A synthetic approach to (-)-diplopyrone

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Description: (+)-Diplopyrone is an optically active phytotoxin isolated from Diploda mutila , an endophytic fungus considered one of the main causes of cork oak ( Quercus suber L.) decline. The focus of this research was a synthetic approach to enantiomeric (-)-diplopyrone from commercially available tri- O -acetyl-D-galactal. The main strategy in this project was the formation of the C -glycoside linkage. We were unable to create a C -glycoside via the samarium-Barbier coupling. We prepared a C-1 nitrile via the Ferrier rearrangement in good yield, but were unable to transform it into the hydroxyethyl group found on (-)-diplopyrone. Initial attempts to convert the nitrile to an aldehyde or ketone using Grignard or hydride reagents failed. We also sought to form a lactone using ring closing metathesis, but were unable to form the vinyl RCM precursor. We were able to functionalize the C-6 position to an aldehyde, but attempts to form a vinyl group via the Wittig, Tebbe, or Peterson reactions failed. We discovered that the nitrile spontaneously eliminates under basic conditions through an E 2 ' mechanism to form a conjugated system. A compound was synthesized that should be unable to react via this mechanism, allowing basic reagents to be used without the formation of side products. We were able to functionalize the C-4 and C-6 positions of the molecule. The C-6 aldehyde was converted to a cis α,β-unsaturated ester via a Z -selective Wittig olefination using a stabilized ylide in methanol. The ester was cyclized to a lactone under acidic conditions to form the nitrile analog of (-)-diplopyrone.
Language: English
Format: Degree Work