benzofurans and eupomatilone-6

An enantioselective synthesis of (-)-5-epi-eupomatilone-6 has been accomplished by using relay catalytic cascade intramolecular hydrosiloxylation and Mukaiyama aldol reaction of 2,3,4-trimethoxy-6-(phenylethynyl)phenyl dimethylsilanol with fluorenylglyoxylate.

Topics: Benzofurans; Catalysis; Glyoxylates; Gold; Molecular Structure; Silanes; Stereoisomerism

The formal synthesis of (+)-3-epi-eupomatilone-6 () and the 3,5-bis-epimer () has been accomplished. The key synthetic strategy involved the stereoselective construction of (3R,4S,5R)- and (3R,4S,5S)-trisubstituted γ-butyrolactones and from (2R,3R)-2,3-dimethyl-4-pentenoic acid derivative , which was readily obtained via stereoselective conjugate addition of vinylmagnesium chloride to a chiral α,β-unsaturated N-acyl oxazolidinone (Evans' auxiliary) followed by α-methylation.

Topics: Benzofurans; Chemistry, Pharmaceutical; Chlorides; Drug Design; Hydrocarbons, Iodinated; Lactones; Magnesium Chloride; Magnetic Resonance Spectroscopy; Methylation; Molecular Structure; Plant Extracts; Stereoisomerism

Fifteen new lignans, gymnothelignans A-O (1-15), bearing tetrahydrofuran with variable conformations belonging to three potentially related skeletons were isolated from Gymnotheca chinensis Decne. The structures were elucidated by means of detailed spectroscopic analysis. Absolute configurations were assigned using X-ray single-crystal diffraction and chemical transformations. Moreover, by the homology, compounds 1-11 and eupomatilones were confirmed to have uniform R-configuration at C-5. However, a synthesized congener has long been mistaken as 5-epimer of eupomatilone-6. This work provides guidance for the absolute configuration establishment of the subeupomatilone family with trans-H-4-H-5 configuration.

Topics: Benzofurans; Biological Products; Crystallography, X-Ray; Furans; Lignans; Magnetic Resonance Spectroscopy; Molecular Conformation; Molecular Structure; Stereoisomerism

Topics: Anhydrides; Benzofurans; Biological Products; Catalysis; Lignans; Organometallic Compounds; Plant Extracts; Rhodium; Stereoisomerism; Zinc

Full details of the total syntheses of five members of the eupomatilone family of lignans are reported.

Topics: Benzofurans; Lignans; Molecular Conformation; Stereoisomerism

This study describes a novel Brønsted acid-catalyzed allylboration method suitable for the most difficult, electronically deactivated allylboronate and aldehyde substrates. This method circumvents the use of metal ions, and rather employs a simple and cheap catalyst, triflic acid. Its usefulness as a complementary allylboration variant was demonstrated with a four-step, stereodivergent synthesis of all four diastereomers of eupomatilone-6 from a single allylboronate. A thorough proof of stereochemistry supported by as many as five X-ray crystallographic structures brings an end to the ambiguity of the original stereochemical assignments. Further to the TfOH-catalyzed allylboration, the synthetic route featured a number of remarkable observations: the surprising reactivity of 2-bromo-3,4,5-trimethoxybenzaldehyde, the subtle reagent control observed in the hydrogenation of an alpha-exo-methylene lactone intermediate, and the success of a difficult case of Suzuki biaryl coupling using Buchwald's conditions.

Topics: Acids; Benzofurans; Boron Compounds; Catalysis; Crystallography, X-Ray; Molecular Conformation; Stereoisomerism

[Reaction: see text]. The Zn-mediated Barbier reaction of the biarylaldehyde 8 with crotyl bromide followed by hydroboration and oxidation provided the gamma-butyrolactones 4 and 5. The stereoselective installation of methyl group at C-3 by using LiHMDS and MeI completed the synthesis of racemic eupomatilone-6 (2) and its diastereomer 3. The spectroscopic data of 2 was in full agreement with reported spectra of natural product, thus confirming the revised relative configuration of eupomatilone-6. Similarly, an optically active (3R,4R,5S)-isomer of eupomatilone-6 (23) was prepared in which the aldol reaction with thiazolidinethione as a chiral auxiliary was employed as a key step. On the basis of the spectroscopic data and optical rotation values of 23, the absolute configuration of eupomatilone-6 was proposed.

Topics: Benzofurans; Crystallography, X-Ray; Hydrogen Bonding; Molecular Conformation; Molecular Structure; Optical Rotation; Stereoisomerism

[reaction: see text] The synthesis of eupomatilone-6 (1) has been achieved by using Suzuki coupling, Sharpless asymmetric dihydroxylation, and intramolecular Horner-Wadsworth-Emmons reactions. The spectroscopic studies carried out on synthetic eupomatilone-6 do not agree with those reported for the natural product, and therefore revision of the assigned structure is warranted.

Topics: Benzofurans; Lignin; Magnoliopsida; Molecular Structure

A novel Ireland-Claisen approach to the putative structure of eupomatilone-6 is described. The rearrangement established the C3 and C4 stereocenters and concomitantly generated a vinyl epoxide. The C5 oxygen was installed by cyclization of the pentenoic acid carboxyl group onto the vinyl epoxide in an S(N)2' fashion to afford the C5-epi stereochemistry. The natural C5 stereochemistry was accessed via a substrate directed dihydroxylation.

Topics: Anti-HIV Agents; Antifungal Agents; Antineoplastic Agents; Benzofurans; Lignans

[structure: see text] A convergent and diastereocontrolled total synthesis of eupomatilones 4 and 6 is reported and was based on a diastereoselective hydroboration/oxidation sequence and a convergent Lipshutz biarylcuprate cross-coupling reaction. The structure of eupomatilone 6 is revised.

Topics: Animals; Benzofurans; Cross-Linking Reagents; Cyclization; Lignans; Molecular Structure; Oxidation-Reduction; Stereoisomerism