Chemical Transformations of the Neoclerodane Diterpenes Eriocephalin and Capitatin:  An Access to 4,5-seco-Neoclerod-5(19)-ene Derivatives

Treatment of the 7-O-acetyl derivative (2) of eriocephalin (1) with HCl yielded minor quantities of the 4,5-seco-neoclerod-5(19)-ene derivatives 3 and 4. Under the same treatment, capitatin (6) underwent an identical fragmentation reaction giving 9 in good yield, via the unstable chlorohydrin intermediate 8. Sodium cyanoborohydride reduction of 9 yielded compounds 10 and 11 by a stereoselective 1,4-reduction process. The mechanistic aspects of these transformations are discussed. The 4,5-seco derivatives 9, 10, and 11 can be useful intermediates for the synthesis of natural and synthetic neoclerodane diterpenoids, which are of interest on account of their activity as insect antifeedants and other important biological properties.