Cheon-Gyu Cho

Total Synthesis of (±)-Galanthamine via a C3-Selective Stille Coupling and IMDA Cycloaddition Cascade of 3,5-Dibromo-2-pyrone

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.

Intramolecular Fischer Indole Synthesis and its Combination with an Aromatic [3,3]‐Sigmatropic Rearrangement for the Preparation of Tricyclic Benzo[cd]indoles

Indoles are arguably the most privileged molecular scaffolds that are present in nature. A wide variety of important biological activities that are exhibited by many indole-based natural products has made them attractive synthetic targets over the years. Accordingly, many elegant methods and strategies have been devised and used for their synthesis. The venerable Fischer indole synthesis, which was reported over 100 years ago, still remains of considerable value for its operational simplicity, despite the limited availability of the starting aryl hydrazines. A few years ago, we reported that aryl hydrazide 1 is an effective surrogate for aryl hydrazines as it readily undergoes a Fischer indolization process to give the corresponding indole 2 (Scheme 1). It was reported more

Total Synthesis of (±)-Crinine via the Regioselective Stille Coupling and Diels−Alder Reaction of 3,5-Dibromo-2-pyrone

The regioselective synthesis and Diels-Alder cycloaddition of 3-(3,4-methylenedioxyphenyl)-5-bromo-2-pyrone provided a new synthetic route to crinine. The vinyl bromide group can be used as a handle for further derivatization.

One step preparation of bromo-2-pyrones via bromo-decarboxylation of 2-pyrone-carboxylic acids

Abstract Synthetically valuable 3-bromo-2-pyrone, 3-bromocoumarin, 5-bromo-2-pyrone, and 3,5-dibromo-2-pyrone were prepared in one step from readily available 2-pyrone-carboxylic acids via bromo-decarboxylation in good to fair yields.

Total syntheses of (+/-)-crinine, (+/-)-crinamine, and (+/-)-6a-epi-crinamine via the regioselective synthesis and Diels-Alder reaction of 3-aryl-5-bromo-2-pyrone.

We have devised a new unified synthetic protocol to (+/-)-crinine, (+/-)-crinamine, and (+/-)-6a- epi-crinamine from the Diels-Alder cycloadduct of 3-(3,4-methylenedioxyphenyl)-5-bromo-2-pyrone with TBS vinyl ether. The requisite 3-(3,4-methylenedioxyphenyl)-5-bromo-2-pyrone was prepared from the C3-selective Stille coupling reaction of 3,5-dibromo-2-pyrone. Also noted is that the vinyl bromide can be used as a handle for further derivatization.

Stille couplings of 3-(trimethylstannyl)-5-bromo-2-pyrone for the syntheses of 3-aryl-5-bromo-2-pyrones and their ambident dienyl characters

Abstract 3-(Trimethylstannyl)-5-bromo-2-pyrone underwent facile Stille coupling reactions with aryl halides to produce various 3-substituted 5-bromo-2-pyrones. The resulting 3-aryl-2-pyrone derivatives underwent both normal and inverse electron demand D-A cycloadditions depending on the type of the dienophiles being reacted.

Intramolecular Fischer indole synthesis in combination with alkyne hydroarylation: synthesis of tetracyclic chromeno-indoles.

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.

Regioselective Stille coupling reactions of 3,5-dibromo-2-pyrone with various aryl and vinyl stannanes

Abstract 3,5-Dibromo-2-pyrone underwent facile regioselective Stille coupling reactions with aryl, heteroaryl and vinyl stannanes to produce various 3-substituted, 5-bromo-2-pyrones. Addition of a catalytic amount of CuI greatly increased the selectivity and chemical yield of the desired 3-aryl-5-bromo-2-pyrone. Second Stille coupling reactions on the resulting 3-aryl-2-pyrones gave rise to a series of potentially useful 2-pyrones with two different functionalities at C3 and C5 position in good to excellent isolated yields. 2-Pyrones with pyridyl groups at C3 position can undergo Lewis acid catalyzed Diels–Alder cycloaddition reactions with benzyl vinyl ether.

β-Silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone for the total synthesis of (±)-pancratistatin.

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.

Intramolecular Imino Diels−Alder Approach to the Synthesis of the Aspidosperma Alkaloid from 3,5-Dibromo-2-pyrone†

A new synthetic route to the key framework of aspidosperma alkaloid was devised from the cycloadduct of 3-(2-nitrophenyl)-5-bromo-2-pyrone via intramolecular imino Diels-Alder reaction.