Tandem one-pot intra- and inter-molecular McMurry coupling for the synthesis of bisindolostilbenophanes

Treatment of 3 equiv of indole-3-aldehyde with 1,3,5-trimethyl-2,4,6-tris(bromomethyl)benzene and 1,3,5-tris(bromomethyl)benzene gave the tris-alkylated products, which underwent both intra- and inter-molecular McMurry coupling in one-pot with low valent titanium to give indole-based stilbenophanes.     

Synthesis of substituted benzene derivatives by homo- and hetero-coupling of 2-bromobenzaldehyde and bromovinylaldehydes followed by McMurry coupling

A convenient synthetic approach to substituted benzene derivatives by modified Ullmann cross-coupling of 2-bromobenzaldehyde and bromovinylaldehydes followed by intramolecular McMurry coupling has been developed.     

A divergent McMurry coupling of the bis-salisaldehyde with methylene linker: The characterization of a key by-product with the possible pathway formation

The McMurry coupling of a bis-salisaldehyde 3a with methyl linker as the smallest member of its alkyl series is known to give the remarkably lower yield of the corresponding stilbenophanes. The half part of this molecule, unlike bigger analogues, is a good leaving group which affordsthreo isomer of 4H, 4′H–4,4′-bibenzo[d][1,3]dioxine 4 in high diastereoisomeric ratio (99>). A further study showed that the formation of this key by-product is the reason for formation of other by-products, namely, 5a,10b-dihydrobenzofuro[2,3-b]benzofuran 9 and 2-(2,3-dihydrobenzofuran-2-yl)phenol 10. Two reaction pathways for the formation of by-products have been proposed which are responsible for the unusual activity of dialdehyde 3a.     

Utilization of microwave heating in the McMurry reaction for facile coupling of aldehydes and ketones to give alkenes

Microwave heating was applied in high-yield syntheses of alkenes by McMurry coupling of aldehydes and ketones with low-valent titanium. All aldehydes and ketones including sulfur end-capped analogues gave alkenes in isolated yields above 80% without detectable amounts of pinacols.     

Synthesis of (+)-Septicine Using Intramolecular McMurry Coupling: A Chiron Approach

Total synthesis of secophenanthroindolizidine alkaloid (+)-septicine 1 was accomplished using the McMurry coupling for the construction of indolizidine ring, using L-glutamicacid as chiral source.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Synthesis, complexation studies and biological applications of some novel stilbenophanes, indolophanes and bisindolostilbenophanes via McMurry coupling

Various types of stilbenophanes, indolophanes and bisindolostilbenophanes were synthesized by intra-, inter- and tandem intra-, intermolecular McMurry coupling. Some of the indolophanes and bisindolostilbenophanes exhibited significant activity against the growth of various bacteria. Complexation of some of the cyclophanes with TCNQ has also been studied.     

Microwave-assisted McMurry polymerization utilizing low-valent titanium for the synthesis of poly 2,6-[1,5-bis(dodecyloxy)naphthylene vinylene] (PNV)

Poly 2,6-[1,5-bis(dodecyloxy)naphthylene vinylene] is synthesized by microwave-assisted McMurry polymerization utilizing low-valent titanium generated from titanium tetrachloride and zinc. The obtained polymer is fluorescent with an average molecular weight of approximately 65,000 g/mol and a polydispersity of M_w/M_n ≈ 3. Absorption and fluorescence spectroscopy in solution and on spin-cast thin films reveal that the bis-alkoxy substituted PNV has a short effective conjugation length but a quite efficient exciton migration.     

Covalent Crosslinking of Graphene Quantum Dots by McMurry Deoxygenation Coupling

Graphene quantum dots were covalently crosslinked forming ensembles of a few hundred nanometers in size by McMurry deoxygenation coupling reactions of peripheral carbonyl functional moieties catalyzed by TiCl₄ and Zn powders in refluxing THF, as evidenced by TEM, AFM, FTIR, Raman and XPS measurements. Photoluminescence measurements showed that after chemical coupling, the excitation and emission peaks blue‐shifted somewhat and the emission intensity increased markedly, likely due to the removal of oxygenated species where quinone‐like species are known to be effective electron acceptors and emission quenchers.     

Reductive coupling of 1,3-dimethyluracils with benzophenone by low-valent titanium: unusual two-to-one coupling

The reductive coupling of 1,3-dimethyluracil with benzophenone by Zn-TiCl₄ in THF gave unusual two-to-one adduct and its further reduced product. The reductive coupling of 1,3-dimethyl-5-fluorouracil with benzophenone by Zn-TiCl₄ also gave two-to-one adduct. 1,3-Dimethylthymine was, however, completely inert under the same conditions.     

Dioxastilbenophanes—synthesis and charge transfer complexation studies

Intramolecular McMurry coupling of dialdehydes derived from xylenyl dibromide and 4-hydroxy benzaldehyde afforded cis-stilbenophanes along with cyclophane diols. Stilbenophanes with a large cavity were also synthesized. Charge transfer complexations of the stilbenophanes with TCNE, TCNQ and PQT were studied. Some stilbenophanes form a relatively stronger complex with PQT rather than with TCNE and TCNQ.     

Reductive coupling of (azulen-1-yl)carbonyl compounds by low-valent titanium; pinacol/pinacolone rearrangement versus pinacol and alkene generation

The azulen-1-yl group strongly influences the course of the TiCl₄-Zn promoted McMurry coupling of 1-acetylazulene which afforded, along with the normal coupling products, pinacol 2dl and alkene 3, the pinacolone 4. The latter was likely formed via rearrangement of the pinacolate intermediate. An improved, microwave-assisted protocol was developed for this reaction that provided high yields of products in a short reaction time. The steric reaction route is consistent with the proposed mechanism.     

Reductive coupling of aliphatic cyclic imides with benzophenones by low-valent titanium

The reductive coupling of aliphatic cyclic imides with benzophenones by Zn–TiCl₄ in THF gave two- and four-electron reduced products selectively by controlling the reaction conditions. Although cyclic and acyclic products were formed as mixtures in most cases, cyclic dehydrated products could be selectively obtained by heating the product mixtures in the presence of cat. p-TsOH.     

The synthesis of oligoether-substituted benzimidazolium bromides and their use as ligand precursors for the Pd-catalyzed Heck coupling in water

The oligoether-substituted (CH₃(OCH₂CH₂)_n-; n = 1, 2 or 3) benzimidazolium bromides (3-7) and oligoether-linked (-CH₂(CH₂OCH₂)_nCH₂-, n = 1, 2 or 3) bisbenzimidazolium dibromides (8-13) were prepared by quarternization of N-substituted benzimidazoles (1 and 2) with the bulky benzyl bromides (ArCH₂Br: Ar = C₆H₂(CH₃)₃-2,4,6 and C₆(CH₃)₅). trans-Bis(carbene) palladium(II) complexes 14 and 15 derived from 4 and 6 were synthesized by using Ag complexes as carbene-transfer agents in dichloromethane at ambient temperature. In addition, the reactions of 4 and 6 with Pd(OAc)₂ and NaBr gave the Pd(II) dimers 16 and 17 which can readily be cleaved by triphenylphosphine to afford the benzannulated monocarbene (NHC) monophosphine Pd(II) complexes [PdBr₂(NHC)(PPh₃)] (18 and 19). All compounds have been fully characterized by using elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopies. X-ray diffraction studies on single crystals of 19a and 19b confirm the cis square planar geometry. In situ formed complexes from Pd(OAc)₂ and benzimidazolium salts (3-13) and preformed Pd(II) complexes 14, 15, 18 and 19 were tested as catalyst for the Heck coupling reaction in water. The influence of the oligoether and benzyl substituents on N atoms and CH₃-substituents on the 5,6-positions of benzimidazole frame were investigated under the same conditions in the Heck coupling reaction. In situ formed catalysts showed better conversions than the isolated Pd(II) complexes. The length of the oligoether spacer significantly increases the activity. The salts with two benzimidazole moieties connected by an oligoether as the spacer 8-13 showed similar catalytic activities in the Heck coupling reaction with the mono salts 3-7 bearing corresponding oligoethers on the N atom.     

Tetralone Esters as Intermediates for the Synthesis of Podophyllotoxin Derivatives Via Cyclopropanation of Chalcones

Cyclopropyl ester (8a-f) were synthesized by the cyclopropanation of chalcones (7a-e) in dry benzene using powdered sodium in 80-85% yield. Preparation of tetralone ester (4a-e), an intermediate for the synthesis of podophyllotoxin derivatives by Lewis acid (SnCl₄) catalyzed cyclization of (8a-e) is also described here.     

New para-para stilbenophanes: synthesis by McMurry coupling, conformational analysis and inhibition of tubulin polymerisation

The synthesis of a new family of methoxy-substituted [2.7]- and [2.8]paracyclophanes linked by 3-oxapentamethylene-1,5-dioxy and hexamethylene-1,6-dioxy bridges has been carried out by using the McMurry methodology. Related indole compounds were also synthesised. Olefin-to-diol ratios depended on the bridge length, the structure of the aromatic ring and the reaction conditions. Macrocyclisation, the methoxy substituents and the presence of a rigid indole moiety restricted the conformational equilibria, as observed by NMR spectroscopy and according to theoretical calculations. The synthesised compounds display micromolar tubulin polymerisation inhibitory activity. The conformational implications on the tubulin polymerisation inhibitory activity derived from the macrocyclisation when compared with combretastatins, closely related stilbenes, are also discussed.     

A pattern recognition approach to 14-epi-hydrophenanthrene core of the morphine alkaloids based on shikimic acid

An expeditious and stereoselective construction of C-14-epimer of the tetracyclic hydrophenanthrene framework of the morphine alkaloids is described. The core structure is obtained in nine steps in 11% overall yield from shikimic acid via three key transformations: (i) coupling of shikimic acid with 2-iodoisovanillin at C-3 by double S_N2 inversion to form the aryl ether 5; (ii) an intramolecular Heck reaction to construct the dihydrobenzofuran ring and (iii) a McMurry coupling to furnish the hydrophenanthrene core.     

Enantiospecific synthesis of an indolizidine alkaloid, (+)-ipalbidine

Enantiospecific total synthesis of an indolizidine alkaloid, ipalbidine, was achieved starting from (−)-pyroglutamic acid by employing an intramolecular McMurry coupling reaction with a low-valent titanium, as a key step.     

Copper-catalyzed decarboxylative coupling reactions for the synthesis of propargyl amines

When aryl alkynyl carboxylic acids were allowed to react with amines and aldehydes in CH₃CN at 80 °C in the presence of 10 mol % CuI, the desired propargyl amines were formed in good yields. This coupling reaction demonstrated to work across a broad range of reagents including functionalized aryl alkynyl carboxylic acids, aliphatic and aromatic aldehydes, and cyclic and acyclic amines.