STUDIES ON THE PREPARATION OF THE ZIEGLER INTERMEDIATE, A KEY INTERMEDIATE IN THE TOTAL SYNTHESIS OF FORSKOLIN

Preparation of the ''Ziegler key intermediate'' 2 from lactone 3, read ily obtained from hydroxy-beta-ionone, was studied. In a first explora tory approach, lactones II and 13 were obtained but further transforma tions aimed at setting the ring junction were unsuccessful due to unex pected rearrangements. Through a straight forward synthetic sequence i nvolving two new rearrangements, lactone 3 was converted to diosphenol 21 with the desired trans A/B ring junction. 21 was in turn transform ed into the well-known acetonide 2 in a good yield. This constitutes a new formal total synthesis of forskolin. Copyright (C) 1996 Elsevier Science Ltd