Further studies on CAB approach toward chemical conversion of C_(19)-diterpenoid alkaloids to taxoids: synthesis of the vital intermediateC-nor-aconanone

摘要

In the title study, the synthesis of the vital intermediate C-nor-aconanone (3) from 4 was completed through 11 steps, mainly including semipinacol rearrangement, formation of the imines by the treatment of 10 or 20 with NBS, the cleavage of N-C(19) bonds in 11 or 21 by treatment with m-CPBA and subsequently with LTA, as well as the rapture of the N-C(17) bonds in 22 by a modified Nef reaction (NaH/t-BuOH -> KMnO_4/H_2O). One-pot procedure was successfully developed starting from 11 or 21 to afford the N, 19-seco-C-nor product 15 or 22, respectively, in reasonably good yields.