Advances in dearomatization strategies of indoles

Enamines: recent advances in synthetic, spectroscopic, mechanistic, and stereochemical aspects—I

General Information. All reactions were carried out under an atmosphere of argon in flame-dried glassware. The reaction solvents: THF, Et2O, CH2Cl2 were purified by passage over activated alumina. Reagents were used as received from the manufacturer unless otherwise stated. Flash chromatography was carried out using EM reagent silica gel 60 (230-400 mesh). Analytical thin layer chromatography was performed on EM Reagent 0.25 mm silica gel 60-F plates. All TLC plates were visualized by UV fluorescence quenching and were stained with either p-anisaldehyde or ceric ammonium molybdate (CAM). Optical rotations were measured on a Jasco DIP-0181 digital polarimeter with a sodium lamp and are reported as follows: [α]λ °C (c=g/100 mL solvent). Infrared spectra were recorded on a Perkin-Elmer 1600 series FT-IR spectrometer. H-NMR spectra were recorded on a Varian Inova-500 (500 MHz) spectrometer and are reported in ppm using solvent as an internal standard (CDCl3=7.26 ppm). Data are reported as: [δ shift]([s= singlet, d=doublet, t=triplet, q=quartet, m=multiplet, b=broad], [integration], and [J=coupling constant in Hz]). Proton decoupled C-NMR spectra were recorded on a Varian Mercury 400 (100 MHz) spectrometer and are reported in ppm using solvent as internal standard (CDCl3=77.0 ppm). Low and high resolution mass spectra were obtained at the Harvard University Mass Spectrometry Laboratory.

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A cascade cycloaddition strategy leading to the total synthesis of (-)-FR182877.

Alkaloid total synthesis by intramolecular imino Diels-Alder cycloadditions

Polycyclic xanthone natural products: structure, biological activity and chemical synthesis.

2-Methylene-1,3-dicarbonyl compounds reacted with alky vinyl ethers in benzene to give hetero-Diels–Alder reaction products, 3,4-dihydro-2H-pyrans, regioselectively and/or chemoselectively.

Hetero-Diels–Alder reactions of 2-methylene-1,3-dicarbonyl compounds with alkyl vinyl ethers

The Diels-Alder reaction of 1,1-dicarbonylethenes 1 with dienes was investigated. The adduct of the reaction of 1, whose two carbonyl groups were different, with cyclopentadiene showed moderate stereoselectivity and this was explained by FMO theory. However, in the Lewis acid-catalyzed addition, the reaction proceeded with high stereoselectivity to give the exo adduct 3x. This might be due to steric hindrance because the benzene ring cannot orient in the plane of the conjugated system in the metal-chelated enedione 6. Applying this principle to (1'R,2'S,5'R)-5-methyl-2-(1-methyl-1-phenylethyl)cyclohexyl 2-benzoylacrylate (1d), we achieved a diastereomeric Diels-Alder reaction to afford 3x-R, whose structure was confirmed by the X-ray crystal analysis.

Reactivity of 2-Methylene-1,3-dicarbonyl Compounds. Stereoselective and Asymmetric Diels-Alder Reactions.

Elaeocarpus Alkaloids. The Synthesis of (±)-Elaeokanine A, (±)-Elaeokanine B, and (±)-Elaeokanine C

6-Acetoxy-4,7-dimethoxybenzofuran-5-carbonyl chloride (4), prepared from khellin (1) by three steps, was condensed with enamines or lithium enolates. Further treatment with acid afforded the khellin analogues (10). Better yields were obtained with lithium enolates than with enamines.

Studies of the syntheses of heterocyclic compounds containing benzopyrone. Part 2. Syntheses of khellin analogues

A convenient synthesis of a variety of 2, 4-cyclohexadien-1-ones 3-7 is described. Reaction of various phenols 2 having appropriate substituents with an excess of S, S-dimethylsuccinmidosulfonium chloride (Corey-Kim reagent, 1)in the presence of triethylamine proceeded with regioselective methylthiomethylation to give methylthiomethyl, bis(methylthiomethyl), or tris(methylthiomethyl)-2, 4-cyclohexadien-1-ones 3-7 in satisfactory yields.

Toshio Watanabe

Papers

Hetero-Diels–Alder reactions of 2-methylene-1,3-dicarbonyl compounds with alkyl vinyl ethers

Reactivity of 2-Methylene-1,3-dicarbonyl Compounds. Stereoselective and Asymmetric Diels-Alder Reactions.

Elaeocarpus Alkaloids. The Synthesis of (±)-Elaeokanine A, (±)-Elaeokanine B, and (±)-Elaeokanine C

Studies of the syntheses of heterocyclic compounds containing benzopyrone. Part 2. Syntheses of khellin analogues

Convenient Synthesis of 2,4-Cyclohexadien-1-ones by Regioselective Methylthiomethylation of Phenols