AuCl3-Catalyzed Hydroalkoxylation of Conjugated Alkynoates: Synthesis of Five- and Six-Membered Cyclic Acetals.

The AuCl3-catalyzed double hydroalkoxylation of conjugated 7-hydroxyheptynoates offers a convenient route for the synthesis of six-membered cyclic acetals, which are common substructures of polyketide natural products. When conjugated 6-hydroxyhexynoates are used as starting materials, either five-membered cyclic E-enol ethers or the corresponding acetals can be obtained by simply choosing the appropriate reaction solvent. NMR spectroscopic studies were carried out to determine the kinetics and pathway of the latterdomino 5-exo cyclization–hydroalkoxylation reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)