In the last decade the use of homogenous gold catalysts has rapidly grown and become a valuable tool for complex natural product synthesis. Spiroketal natural products are valuable targets for total synthesis and medicinal chemistry applications. The use of gold catalysts has emerged as a useful tool to synthesise these privileged scaffolds. This review summarises the application of gold catalysis for the syntheses of spiro, bridged and fused ketal natural products.
The first total synthesis of resorcyclic acid lactone spiroketal citreoviranol (1) is described. The synthesis was completed in nine steps and via Sonogashira cross-coupling, gold-catalyzed cyclization, and an unusual base-induced ketalization. The relative and absolute stereochemistry of citreoviranol was unambiguously confirmed using 2D NMR spectroscopy and X-ray crystallography.
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