Palladium-catalyzed stereoselective synthesis of E- and Z-1,1-diaryl or triarylolefins

Hydrohalogenation of Ethynylpyridines Involving Nucleophilic Attack of a Halide Ion

Efficient hydrochlorination of 2-ethynylpyridines was achieved without the use of special reagents. Ethynylpyridine readily reacts with hydrochloric acid to form a pyridinium salt. The salt formation considerably enhances the electrophilicity of the ethynyl group and attracts a chloride ion as the counteranion. The spatial proximity facilitates the nucleophilic addition of the halide anion to the ethynyl group, producing 2-(2-chloroethenyl)pyridine in high yields. This protocol could also be applied for hydrobromination and hydroiodination using hydrobromic and hydroiodic acids, respectively. In the case of acetic acid, the reaction did not proceed because of the low acidity and lack of salt formation. This problem was overcome by exchanging the counteranion using silver acetate; the resultant pyridinium acetate underwent hydroacetoxylation.

Self-Assembly of Disorazole C1 through a One-Pot Alkyne Metathesis Homodimerization Strategy

Alkyne metathesis is increasingly explored as a reliable method to close macrocyclic rings, but there are no prior examples of an alkyne-metathesis-based homodimerization approach to natural products. In this approach to the cytotoxic C2-symmetric marine-derived bis(lactone) disorazole C1, a highly convergent, modular strategy is employed featuring cyclization through an ambitious one-pot alkyne cross-metathesis/ring-closing metathesis self-assembly process.

Self-Assembly of Disorazole C1 through a One-Pot Alkyne Metathesis Homodimerization Strategy

Alkyne metathesis is increasingly explored as a reliable method to close macrocyclic rings, but there are no prior examples of an alkyne-metathesis-based homodimerization approach to natural products. In this approach to the cytotoxic C₂ -symmetric marine-derived bis(lactone) disorazole C₁, a highly convergent, modular strategy is employed featuring cyclization through an ambitious one-pot alkyne cross-metathesis/ring-closing metathesis self-assembly process.

Synthesis, biological evaluation, and structure-activity relationships of tri- and tetrasubstituted olefins related to isocombretastatin A-4 as new tubulin inhibitors

The synthesis and structure-activity relationships associated with a series of 1,1-diarylethylene tubulin polymerization inhibitors 3 and 4 are described. The key step for their preparation involves a palladium-catalyzed coupling of N-arylsulfonylhydrazones with aryl halides, thus providing flexible and convergent access to tri- and tetrasubstituted 1,1-diarylolefins 3 and 4 related to isocombretastatin A-4 (isoCA-4). These compounds have been evaluated for tubulin polymerization inhibitory activity as well as for cytotoxic activity. The most potent compounds are 1,1-diaryl-2-methoxyethylenes 4b, 4d and 4e having a trisubstituted double bond. They exhibited good antiproliferative activity against various human cancer cell lines (GI(50) = 8-80 nM). Compounds 4b and 4e strongly inhibited tubulin polymerization with IC(50) values of 2 and 3 μM, respectively, and induced cell cycle arrest in the G(2)/M phase in the K562 cell line. Docking studies in the colchicine binding site of tubulin allowed identification of residues most likely to interact with these inhibitors and explain their potent anti-tubulin activity.

Stereospecific synthesis and structure-activity relationships of unsymmetrical 4,4-diphenylbut-3-enyl derivatives of nipecotic acid as GAT-1 inhibitors

Two complementary stereospecific synthetic approaches for the preparation of unsymmetrical ortho-substituted N-(4,4-diphenylbut-3-enyl) derivatives of nipecotic acid are described. Determination of the activity of the prepared compounds at the GAT-1 transporter highlighted differing SAR requirements of the E- and Z-phenyl rings, and led to the discovery of a compound with comparable potency to tiagabine. Some attempts to replace nipecotic acid with alternative novel amino acids are also described.

Regiocontrol of the Palladium-Catalyzed Tin Hydride Addition to Z-Enynols: Remarkable Z-Directing Effects

Palladium-catalyzed hydrostannation of substituted Z- and E-enynols is discussed and compared. The regioselectivity of the H-Sn bond addition was found to be controlled by the geometry of the double bond (Z- or syn-directing effect) rather than the nature of its substituents. Exclusively alpha-vinyl stannanes were obtained from Z-enynols having various substituents on the double bond regardless of their electronic, steric, or chelating natures.

Significant enhancement of the Stille reaction with a new combination of reagents-copper(I) iodide with cesium fluoride

The combination of copper(I) iodide and cesium fluoride significantly enhances the Stille reaction. After extensive optimisation, a variety of electronically unfavourable and sterically hindered substrates were coupled in very high yields under mild conditions.

Platinum Oxide Catalyzed Hydrosilylation of Unsymmetrical Internal Aryl Alkynes under Ortho-Substituent Regiocontrol

[chemical reaction: see text]. PtO2- and H2PtCl6-catalyzed hydrosilylation of internal aryl alkynes having a para or an ortho substituent with triethylsilane are discussed and compared. The regioselectivity of the H-Si bond addition was found to be controlled by the ortho substituent rather than the nature of the platinum catalyst. Arylalkynes with an ortho substituent, regardless of its electronic nature, directed the silyl substituent mainly to the alpha-position. PtO2 proved to be a versatile and powerful catalyst compared to H2PtCl6 since it prevents the alkyne reduction.

Sequential Reactions of Trimethylstannyl Anions with Vinyl Chlorides and Dichlorides by the SRN1 Mechanism Followed by Palladium-Catalyzed Cross-Coupling Processes

The reactions of trimethylstannyl ions (Me(3)Sn(-)) with vinyl chlorides in liquid ammonia give good yields of vinylstannanes. Some of them react in the dark, and others need light stimulation to react. The fact that these reactions are inhibited by radical and radical anion traps shows that they occur by the S(RN)1 mechanism. When the reaction takes place with 1,1-dichloro-1-alkenes, monosubstitution reduced products are formed in an E/Z mixture. The efficient synthesis of triarylolefins by Pd(0)-catalyzed cross-coupling reactions of vinylstannanes with several iodoarenes is reported. Similar yields were obtained in one-pot-type reactions.