Tellurium in organic synthesis: synthesis of bioactive butenolides

Reduction of (Z)-β-butyltelluro-enones gives the corresponding γ-hydroxy vinylic tellurides with retention of the double bond configuration. Reaction of γ-hydroxy vinylic tellurides with 2 equiv of n-butyllithium produces 1,4-C,O-dianions, which on reaction with carbon dioxide give the corresponding butenolides.     

Tellurium in organic synthesis: an approach to the synthesis of (Z,E)-dienic precursors of insect pheromones

A simple and straightforward route to (Z,E)-dienic precursors of insect pheromones was developed. The route features a cross-coupling of a (Z,E)-dienic telluride with an alkyl Lipshutz cuprate.     

The LILITH approach to organic synthesis planning

The general basis of the LILITH program is outlined. The size of the possible solution space is reduced by enhancing convergence, simplification and ordering. Complexity distance, relevant bond sets and ordering for bond-forming sequences are described. The evaluation of reactivity is the second main aspect in organic synthesis planning. Properties involving the ground state (native bond polarity) and the excited state (group-similar interference) contribute to the prediction of reactivity.     

Tellurium in organic synthesis: X. Synthesis of 3-halogenobenzo [b] tellurophene derivatives

Several substituted 3-halogenobenzo[b] tellurophenes have been synthesized by treating phenylacetylenes with TeO₂ in acetic acid in the presence of a lithium halide. A mechanism is postulated involving an electrophilic attack by a solubilized tellurium species on the acetylenic bond with introduction of a halogen atom followed by cyclization to the benzo[b]tellurophene system. The benzo[b]tellurophenes can be easily chlorinated with Cl₂ gas to yield benzo[b]tellurophene 1,1-dichloride derivatives, but attempted lithiation is the 3-position was unsuccessful and resulted in a ring rupture. When refluxed in trifluoroacetic acid 3-chlorobenzo[b]tellurophene was converted into 3-oxo-2,3-dihydrobenzo[b]tellurophene.     

Tellurium in organic synthesis: the enantioselective synthesis of the pheromone blend components of Mayetiola destructor,Drosophila mulleri and Contarinia pisi

The components of the pheromone blend of Mayetiola destructor, Drosophila mulleri, and Contarinia pisi were synthesized in high enantiomeric excess (99% ee) from a common enantiopure dianion prepared from an enantiopure hydroxytelluride.     

Towards a universal organogelator:A general mixing approach to fabricate various organic compounds into organogels

Low-molecular-weight organogels(LMOG) have been attracting a surge interest in fabricating soft materials.Although the finding of the gelator molecules has been developed from serendipity to objective design,the achievement of the gelator molecules still needs good design and tedious organic synthesis.In this paper,we proposed a simple and general mixing approach to get the organogel for nearly all the organic compounds and even soluble nanoparticles without any modification.We have designed a universal gel...     

Benzothiazines in organic synthesis. An approach to floresolide B

The intramolecular conjugate addition of a sulfoximine carbanion to an α,β-unsaturated ester results in the formation of a benzothiaine bearing a benzylic stereocenter with extremely high fidelity. We have used this methodology to complete a formal total synthesis of the antitumor agent (+)-floresolide B.     

Asymmetric total synthesis of (+)-luciduline: toward a general approach to related Lycopodium alkaloids

As part of a research program directed toward the synthesis of Lycopodium alkaloids, a multigram scale asymmetric synthesis of intermediate 11 was achieved in 11 steps from pyridine (17). In addition to our alkene metathesis strategy, a key feature of this synthetic approach consists of a Fukuyama's Diels-Alder cycloaddition between 1,2-dihydropyridine and acrolein using MacMillan's catalyst (18) on a 50 g scale. This led to a 12-step catalytic asymmetric synthesis of (+)-luciduline (1). A broader subset of Lycopodium alkaloids could also be obtained, as demonstrated by the derivatization of 11 into advanced intermediates for the synthesis of some of these natural products.     

A general approach to the synthesis of 1-deoxy-L-iminosugars

A stereoselective procedure for the preparation of non-naturally occurring deoxy iminosugars belonging to L-series has been developed. The synthesis involves the construction of the key intermediate bicycle pyperidine 8, available in few steps by the coupling of the heterocyclic synthon 3 and the readily available Garner aldehyde 4.     

A general approach to triphenylenes and azatriphenylenes: total synthesis of dehydrotylophorine and tylophorine

A convergent and flexible synthesis of substituted triphenylenes, azatriphenylenes, and the cytotoxic alkaloids dehydrotylophorine and tylophorine has been developed.     

Tellurium azamacrocycles: synthesis, characterization and coordination studies

The metal-free condensation of bis(2-formylphenyl) telluride (1) with a series of diamines affords macrocyclic tellurium ligands 2-7. Crystals of the protonated macrocycle 8 are monoclinic, space group P2/n with a=10.890(5), b=7.414(4), c=24.334(13) Å, Z=2. The reaction of tellurium containing macrocyclic Schiff base 2 with Pd(C₆H₅CN)₂Cl₂ gives the expected 1:1 product [Pd(II) 2] Cl₂ (9). Complex 9 was treated with excess of NH₄PF₆ in methanol to give the analogous PF₆⁻ salt [Pd(II) 2] (PF₆)₂ (10). The crystals of 10 are monoclinic, space group P2₁/n, a=8.2250(10), b=21.280 (4), c=21.150 (4), Z=4. However, the reaction of 2 with Pt(COD)Cl₂ proceeds via novel transmetallation to yield an organoplatinum complex (11). The crystals of 11 are also monoclinic, space group P2₁/n, a=12.3253 (14), b=14.6557 (14), C=13.4054 (11), Z=4. The octahedral Ni(II) complex 12 was prepared by the reaction of NiCl₂ · 6H₂O with 2 and NH₄PF₆ under an inert atmosphere. For 12: triclinic, space group ; Z=2; a=10.800(8), b=13.468(9), c=13.918(11), α=89.67(6)°, β=101.53(7)°, γ=81.49(3)° and V=1961(3). Cyclic voltammetry of 12 in MeCN solution shows a well-behaved quasi-reversible (ΔE=100 mV) Ni(III) ↔ Ni(II) couple.     

Development of a general approach to the synthesis of a library of isoflavonoid derivatives

Isoflavonoids are a class of organic compounds that act primarily as antioxidants. They are produced almost exclusively by various members of the bean family including soybeans, tofu, peanuts, chick peas, and alfalfa. The antioxidant characteristics that isoflavonoids exhibit help hinder the progression of certain cancers, primarily breast, prostate, and colon cancer. We have developed a three-five step synthesis for obtaining a suite of isoflavonoid derivatives. The synthesis involves an enamine formation, a ring closure and halogenation, a Suzuki coupling, and finally a global deprotection to obtain the respective isoflavonoid derivatives.     

Copper-catalyzed cross-coupling of amides and potassium alkenyltrifluoroborate salts: a general approach to the synthesis of enamides

Potassium alkenyltrifluoroborate salts undergo coupling with amides to give enamides using a catalytic amount of Cu(OAc)₂ under mild oxidative conditions. The air and water stable alkenyltrifluoroborate salts offer a practical alternative to the use of alkenyl halides and alkenylboronic acids as cross-coupling partners. A range of amides participate in the cross-coupling, including heterocyclic amides, imides, carbamates, benzamides, and acetamides. Optimization studies established two sets of conditions, best suited to either high pK_a or low pK_a amide substrates. Lower pK_a amide substrates worked best using a dichloromethane solvent system in the presence of 4 Å molecular sieves, 10 mol % Cu(OAc)₂, and 20 mol % N-methylimidazole. Higher pK_a amide substrates worked best using a ‘ligandless’ protocol using a 1:1 dichloromethane/DMSO solvent system in the presence of 4 Å molecular sieves and 10 mol % Cu(OAc)₂. The cross-coupling reactions occur stereospecifically with retention of alkene configuration from the alkenyltrifluoroborate salt. The mild reaction conditions employed are tolerant of various functionalities, including nitro, acetals, alkyl and aryl halides, and α,β-unsaturated carbonyls. Finally, the importance of copper sources and the presence of minor impurities were investigated.     

Alkoxy radicals in organic synthesis. A novel approach to spiroketals

Photolysis of an unsaturated alcohol in the presence of HgO and iodine generates an alkoxy radical which can cyclize to form a five-membered ring ether. If a hemiketal is employed, a spiroketal can be formed in good yield.     

A new approach to synthesis of organic/inorganic nanocomposites

The possibility of preparation of nanocomposite materials with improved physicomechanical properties by polycondensation of spirocyclic silicates and diisocyanates was elucidated. The thermomechanical, spectral, and thermogravimetric properties of the resulting materials were examined.     

An iterative approach to the synthesis of thiophene-based organic dyes

We developed an iterative synthetic method for oligo-aryl compounds using an organosilicon-based palladium-catalyzed cross-coupling reaction. Aryl compounds containing a benzyloxy(diisopropyl)silyl group (masked Si group) had sufficient chemical stability, and the unmasking step proceeded in a high yield under mild conditions. Both of the key unmasking/coupling steps required no strict anhydrous or degassed conditions. The developed procedure was used for the synthesis of thiophene-based organic dyes for dye-sensitized solar cells.     

Tellurium in organic synthesis : V. X-ray structure of 8-ethoxy-4-cyclooctenyltellurium trichloride and its relevance to the TeO2-oxidation of alkenes

The molecular structure of 8-ethoxy-4-cyclooctenyltellurium trichloride has been determined from three-dimensional X-ray diffraction data. The crystal belongs to the monoclinic system, space group P2₁/n, with four formula units in a cell of dimensions: a 7.712(1), b 13.406(3), c 13.820(2) Å and β 95.18(1)°. The structure was solved by the conventional heavy atom method, and refined by the least-squares procedure to R = 0.025 for 2199 reflections.The compound is formed from the corresponding β-chloroalkyltellurium tri-chloride, obtained from TeCl₄ and cis, cis-1,5-cyclooctadiene, by an unusually mild solvolytic substitution reaction in ethanol. Similar β-chloroalkyltellurium compounds are postulated as intermediates in the TeO₂ oxidation of alkenes to alkanediol diacetates and alkanediol monoacetates in HOAc containing a lithium halide, LiX. Oxidation of cis-2-butene and trans-2-butene with TeO₂/HOAc/LiBr gave a high preference for cis-stereochemistry in the products while 1-decene showed no stereospecificity.     

A liquid-phase approach to functionalized Janus dendrimers: novel soluble supports for organic synthesis

A new kind of functionalized Janus dendrimer has been synthesized via a liquid-phase approach, which could easily be purified using a simple precipitation method without the need for chromatographic separation. Their use for liquid-phase organic synthesis has been achieved in the Pd-catalyzed Suzuki coupling reactions, giving biaryl products in excellent yields after cleavage.