TOTAL SYNTHESIS OF ULEINE-TYPE AND STRYCKNOS ALKALOIDS THROUGH A COMMON INTERMEDIATE

A stereoselective total synthesis of the alkaloids of the uleine group, dasycarpidone, dasycarpidol, and nordasycarpidone, has been accomplished from the tetracyclic intermediate 1, which has been prepared by two alternative routes, either by Fischer indolization of 2-azabicyclo[3.3.1]nonanone 9 or, more efficiently, by stereocontrolled cyclization of 2-[(2-cyano-3-ethyl-4-piperidyl)methyl]i 24a and 24b. From the same tetracyclic intermediate 1, the Strychnos alkaloid tubotaiwine was also synthesized, the key step being the construction of the quaternary spiranic center by cyclization of a thionium ion upon the indole beta-position.