Stereoselective synthesis and cyclisation of the acyclic precursor to auripyrone A and B

The acyclic precursor to the auripyrones has been synthesized by a stereoselective aldol strategy. This compound fails to undergo cyclisation to form the spiroacetal dihydropyrone ring system found in auripyrone A and B; instead, it forms a dihydropyrone ring by cyclisation of the C11 hydroxyl onto the C15 carbonyl with subsequent dehydration. In contrast, a model compound was prepared and shown to cyclise to both the spiroacetal dihydropyrone ring system and the dihydropyrone ring.