Progress toward the total synthesis of the epoxyquinoid family of natural products
Snyder, Lee J
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Enyne metathesis is a powerful C-C bond forming reaction that combines an alkene and an alkyne and forms a conjugated 1,3-diene. The scope of enyne metathesis was expanded by combining various alkynes with vinyl ethers. Typically vinyl ethers are poor metathesis substrates, but a method was developed for the synthesis of dienol ethers utilizing ruthenium carbenes. The products of these reactions were subjected to [4+2] cycloaddition conditions to give substituted cyclohexene rings. The epoxyquinoid family is a highly targeted series of natural products. A general method for the synthesis of the core structure of these natural products has been explored. An enyne cross metathesis/ring closing metathesis step was designed as the key reaction to this synthesis. A Darzen's condensation between a chiral [alpha]-alkoxy aldehyde and a chloroacyl oxazolidinone was successfully employed to join two fragments of the molecule as well as to install an epoxide. A highly diastereoselective cuprate addition set the stereochemistry of the first stereogenic center. The early intermediates were prepared via easily scalable organic syntheses procedures including utilizing a carbohydrate as the source of chirality. Ring closing enyne metathesis to form the epoxyquinoid core was evaluated in two epimeric series.