A carbohydrate based chiron approach to the lactone intermediate employed in the synthesis of BC-ring fragment of (+)-spirastrellolide A

A concise and stereoselective synthesis of the key intermediate used for constructing the BC-ring fragment of (+)-spirastrellolide A is described. The synthetic sequence represents a chiron approach that employs readily available and inexpensive l-arabinose and sets up the stereochemical triad at C20–C22 all from the sugar. This lactone can be used to assemble the spiroketal in the Southern Half through a cyclic acetal-tethered ring-closing metathesis strategy, and is poised for connecting with the Northern Half at C24–C25.