Cheon Gyu Cho

A new efficient synthetic route to (+/-)-galanthamine was devised by using a tandem C3-selective Stille coupling-IMDA cascade of 3,5-dibromo-2-pyrone as a key strategy.

Aryl hydrazides underwent the Fischer indolization reactions, while the N-carbamate group(s) remained intact to directly provide N-Cbz-indoles. This new method allowed the synthesis of various N-Cbz-carbazoles and N,N'-bis-Cbz-pyrrolo[2,3-f]indoles.

At the end of the tether: Aryl hydrazides that have carbonyl groups tethered at the para position of the aromatic ring undergo an intramolecular Fischer indolization reaction to give the corresponding indolophanes. Strategic insertion of a double bond in the tether enables a tandem aromatic [3,3] sigmatropic rearrangement reaction to occur to give tricyclic benzo[cd]indoles.

A visible-light-induced synthesis of N -H carbazoles from easily accessible 2,2′-diaminobiaryls in the absence of any external photosensitizer is reported. The process only requires t BuONO and natural resources, visible light, and molecular oxygen for the synthesis of N -H carbazoles. Experimental and computational studies support that the in situ formation of a visible-light-absorbing photosensitizing intermediate, benzocinnoline N -imide, is responsible for the activation of triplet molecular

D-A cycloadditions of 3,5-dibromo-2-pyrone were investigated with a series of electronically and sterically distinct dienophiles. Our results showed that it is a highly potent ambident diene, being more reactive and stereoselective than monobromo-2-pyrones, and thus capable of generating a variety of bicycloadducts in much higher chemical yields and endo/exo ratios than monobromo-2-pyrones. Another interesting feature of this study is that the two bromine groups on the cycloadducts could be inde

A new synthetic route to (±)-lycorine, starting from the endo-cycloadduct of 3,5-dibromo-2-pyrone and (E)-β-borylstyrene, is reported. Boronate oxidation and a set of reactions including face-selective epoxidation provided the pivotal C1-OH group and C3/C3a double bond.

Aryl hydrazides with a ketone or aldehyde containing side chains linked to the meta-position of the aromatic ring undergo acid-promoted intramolecular Fischer indole synthesis to generate 3,4-fused tricyclic indoles. The preparative utility of this conceptually new synthetic approach, which does not require prefunctionalization of the indole ring, was demonstrated by its application to a concise total synthesis of (-)-aurantioclavine.

Ene-hydrazide prepared from enol triflate undergoes a Fischer indolization reaction to give the corresponding indole with complete regioselectivity. The starting enol triflate is readily accessed in regiochemically defined form from the ketone precursor via various well-established methods. This new protocol was successfully applied to the synthesis of desbromoarborescidine A, a natural β-carboline alkaloid, difficult to prepare with conventional Fischer indole synthesis.

Aryl hydrazides bearing a carbonyl function connected through an alkyne tether underwent an intramolecular Fischer indolization and alkyne hydroarylation in a tandem fashion to afford novel tetracyclic chromeno-indoles. The accompanying isomerization of the 2H-chromene double bond can be avoided by stopping the tandem process at the indolophane stage and conducting the alkyne-hydroarylation reaction separately in the absence of a proton source.

A conceptually new synthetic approach that provides general access to the aspidosperma alkaloids (+)-aspidospermidine and (-)-tabersonine was developed. This method is based on the regioselective indolization of an ene-hydrazide, which was obtained via a base-catalyzed intramolecular aza-Michael reaction, in situ trapping of the resulting enolate, and subsequent C-N coupling with phenyl hydrazide.

A new synthetic route to (±)-pancratistatin was devised utilizing β-silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone. The TMS group incorporated in the cycloadduct permitted a facile elimination process for the eventual installation of the C(1)-OH function. Subsequent transformations including Curtius rearrangement and Bischler-Napieralski reactions completed the total synthesis of (±)-pancratistatin.