A MODULAR ENANTIOSELECTIVE APPROACH TO CONSTRUCTION OF THE MACROLACTONE CORE OF POLYCAVERNOSIDE-A

A program directed toward a total synthesis of polycavernoside A is de scribed. The synthesis of five building blocks is detailed. The first of two electrophilic units, the lactone 3, was prepared in four steps from the known enantiomerically pure oxirane 15. Pyranyl aldehyde 5 wa s elaborated in turn from L-malic acid via 10. While the route to 30 i nvolved 3 as a starting material, dithiane 2 was obtained in a straigh tforward manner from 10 as well. The merging of the chiral sectors cou ld not be accomplished by way of the lithiated dithianyl anions, presu mably as a consequence of their heightened basicity. The strategic inc orporation of the trienyl sector was accomplished, although no attempt was made to control the diastereoselectivity of the process.