Abstract
Results of the studies directed to total synthesis of C_<20>-gibberellins are presented. Starting from the tetracyclic enone 2, the key intermediate for our total syntheses of diterpene alkaloids, compound 37 having the ABCE ring system of the gibbane skeleton was synthesized in a stereocontrolled manner and in good yield. Hydrocyanation of the hydrindenone derivative 18 to the cis hydrindanyl carbonitrile 19 was effected in excellent yield with diethylaluminum cyanide in methylene chloride. A new method for formylolefination was successfully applied to the angular carboxaldehydes (33 and 36) giving 34 and 37 in excellent yields. In a model experiment using steroid molecule, a new one-step method for building-up of the BCD ring system was established (42→43). Another model experiment for construction of the AE ring system was accomplished using the tetracyclic secondary amine 46 giving 49. Investigation for conversion of 37 into gibberellin A_<15> is in progress.
