Synthesis of central spiro-bis-THF fragments of symbiospirols A-C

The gold catalysed alkynediol spiroketalization to assemble the central spiro-bis-THF fragments (C22-C33 and C36-C47) of symbiospirols A-C is documented. The adopted chiral pool approach employed commercially available d -glucose and l -malic acid in the synthesis of key building blocks. In addition, two other possible diastereomers have been synthesized in order to establish the relative stereochemistry of the unassigned THF-center of symbiospirols B/C. Four diastereomeric spiro-bis-THF derivatives representing the central C22-C33 and C36-C47 fragments of symbiospirols A-C have been synthesized in an attempt to establish the relative stereochemistry of these fragments.