Synthetic studies on polycyclic indole alkaloids
The first part of this work details the formal total synthesis of HKI 0231B and the first total synthesis of both demethyl HKI 0231A and demethyl HKI 0231B. The formal synthesis used TBAF as a mild reagent to construct the indole. The total synthesis featured an efficient radical cyclization/oxidation step to construct the skeleton and a DDQ-mediated methoxylation reaction;The second part of this work is dedicated to the synthetic efforts towards the abeo-ergolines and the total synthesis of the abeo-ergoline analogs. In the synthetic study toward the abeo-ergolines, a reaction between 4-lithioindole and the enaminone, which was prepared from the ketone and Brederick reagent, effectively brought together all the necessary carbons for the final product. The synthesis of the abeo-ergoline analogs was direct, as it had a 36% overall yield in 7 steps. This approach is also flexible enough to allow the synthesis of various structurally related abeo-ergoline analogs;The third part of this work describes the invention of a new strategy which allows the one-pot benzocyclobutenol synthesis and the corresponding three-component reactions. In the reaction, acetaldehyde enolate and benzyne intermediates were generated in the same flask to produce benzocyclobutenoxides species which is in equilibrium with o-qunodimethide species. With protonation, benzocyclobutenols were prepared in a one-pot fashion. With the addition of dienophiles, three component reactions were achieved. This strategy was also successfully applied in the synthesis of the berbine natural products when cyclic imines were used as dienophiles.