Synthetic Study toward the Misassigned (±)-Tronoharine

The
synthesis of a pentacyclic indole compound corresponding to
the core structure of the misassigned indole alkaloid, tronoharine
(1), is presented. The key reactions were a formal [3
+ 3] cycloaddition of an indol-2-yl carbinol with an azadiene for
the construction of the 6/5/6/6 tetracyclic system containing an all-carbon
quaternary center and an intramolecular substitution reaction of an
amine and a triflate for the creation of the bridged azepine ring.
In addition, some other interesting transformations discovered during
the synthetic studies are also discussed.