Copper-catalyzed Z-selective semihydrogenation of alkynes with hydrosilane: a convenient approach to cis-alkenes

A copper catalyst generated in situ from widely available copper salt and imidazolium salt in the presence of t-BuOK showed high efficiency for the semihydrogenation of a wide range of internal and terminal alkynes to their corresponding alkenes without obvious over-reduction. Functional groups, such as hydroxyl, nitro, halides, and amino, etc. were tolerated. The Z/E ratios of the obtained alkenes were generally >99%. Finally, semireduction of bulky alkynes also went smoothly.     

Concise synthesis of multiply substituted stereodefined cis,cis-2,4-diene-1,6-dials, cis,cis-2,4-diene-1,6-diols and further applications

Reactions of 1,4-dilithio-1,3-dienes with DMF afforded multiply substituted stereodefined cis,cis-2,4-diene-1,6-dials in high yields. Treatment of these 1,6-dials with LiAlH₄ or RLi resulted in the formation of their corresponding 1,6-diols. These bifunctional compounds, cis,cis-2,4-diene-1,6-dials and -1,6-diols are otherwise not readily available. Further reaction of these 1,6-diols with an aldehyde catalyzed by strong acids led to the formation of oxacycles of novel structures.     

Rapid synthesis of indole cis-enamides via hydroamidation of indolic alkynes

The synthesis of indolic cis-enamides using a ruthenium-mediated hydroamidation of indole alkynes with primary oxalamides or α-keto amides is reported. Using this method the total synthesis of igzamide and Z-coscinamides A and B has been achieved.     

Room temperature ionic liquids promoted three-component coupling reactions: a facile synthesis of cis-isoquinolonic acids

Room temperature ionic liquids are found to catalyze efficiently the three component-coupling reactions of aldehydes, amines and homophthalic anhydride under mild and convenient conditions to afford the corresponding cis-isoquinolonic acids in excellent yields with high cis-selectivity.     

Synthesis of cis-3,4-diarylpiperidines and cis-3,4-diaryltetrahydropyrans

Substituted cis-3,4-diarylpiperidines and cis-3,4-diaryltetrahydropyrans are synthesized in modest overall yields starting from 4-aryl-1,2,5,6-tetrahydropyridines and 4-aryl-1,2,5,6-tetrahydropyrans via the following sequence: (1) pinacol-type ring contraction having the combination of m-chloroperoxybenzoic acid and boron trifluoride etherate, (2) Grignard addition with arylmagnesium bromide reagents and followed by boron trifluoride etherate-mediated intramolecular ring-expanded rearrangement, and (3) hydrogenation with hydrogen on 10% palladium-activated carbon. A facile synthesis of 3,4-diarylpyridines was also described by base-induced aromatization.     

Rhodium catalyzed synthesis of isoindolinones via C-H activation of N-benzoylsulfonamides

An efficient approach to a wide range of isoindolinones, including 3-monosubstituted and 3,3-disubstituted isoindolinones, from the annulation of N-benzoylsulfonamides with olefins and diazoacetate has been developed. The transformation is broadly compatible with both terminal and internal olefins. Moreover, diazoacetate is for the first time incorporated into an amide-directed C-H functionalization reaction. Specifically, the rhodium complex [{RhCl₂Cp*}₂] enables the in situ dimerization of diazoacetate in addition to its role in catalyzing C-H functionalization/cross-coupling.     

Triazolopeptides: chirospecific synthesis and cis/trans prolyl ratios of structural isomers

As cis/trans prolyl isomerization plays a crucial role in various biological processes, peptide mimics capable of modifying the cis/trans Xaa-Pro ratio are of particular interest. A practical approach toward proline derived triazolopeptides employing [3+2] azide-alkyne cycloadditions as the key reaction step and the analysis of their cis/trans prolyl ratios are reported. Structural investigations indicated the adjustability of both the cis-percentage and the conformational stability toward intramolecular H-bonding effects.     

Microwave-assisted efficient synthesis of 1,2-diaryldiketones: a novel oxidation reaction of diarylalkynes with DMSO promoted by FeBr3

This paper reports the oxidation of functionalized diarylalkynes with DMSO in the presence of the environmentally friendly FeBr₃ catalyst. This non-toxic procedure is general and has been applied successfully under microwave irradiation leading rapidly to benzil derivatives in good yields.     

New synthesis of cis-3,4-diaryl-1-tosylpyrrolidines

Unsymmetrically substituted cis-3,4-diarylpyrrolidines are synthesized in nearly 25% overall yields starting from 4-aryl-1,2,5,6-tetrahydropyridines by iterative reactions using the combination of m-chloroperoxybenzoic acid (MCPBA) and boron trifluoride etherate (BF₃·OEt₂) followed by Grignard addition, elimination and hydrogenation sequence.     

Cationic cyclization of keto-epoxides mediated by zirconium(IV) tetrachloride: diastereoselective synthesis of cis-decalinols

10-Methyl-cis-9-decalinols are important motifs in several natural products and key intermediates in total synthesis. Herein, we wish to describe a highly chemo- and diastereoselective cyclization of keto-epoxides leading to 10-methyl-cis-9-decalinols. This method based on the use of zirconium(IV) tetrachloride permits the access to a wide variety of cis-decalinols in good to excellent yields. The cationic cyclization could also be performed with chiral keto-epoxide with complete control of the diastereoselectivity affording cis-bicyclic tertiary alcohol with good enantiomeric excess. The chemo- and the diastereoselectivity are assumed to result from the ability of Zr(IV) to generate highly stable bidentic complexes with α-hydroxy-ketone intermediates.     

Synthesis and characterization of high cis-polybutadiene: influence of monomer concentration and reaction temperature

This paper reports the study of the dependence of reaction conversion, catalyst activity, polymer microstructure, molecular weight, molecular weight distribution curves and Mooney viscosity on reaction temperature and monomer concentration in the reaction medium used in the synthesis of high cis-polybutadiene. A ternary catalyst system composed by neodymium versatate, trans-butyl chloride and diisobutylaluminum hydride was used in its synthesis. The highest molecular weights were obtained at polymerization temperatures in the range from 70 to 80 °C. The highest content of cis-1,4 repeating units (about 99%) was observed when the polymerization was carried out at the lowest initial monomer concentration (0.56 mol/l).     

Oxidation of alkenes with non-heme iron complexes: suitability as an organic synthetic method

In the course of a preliminary study to determine the preparative value and the synthetic applications of the non-heme iron(II) complexes Fe(bpmen)(OTf)₂ and Fe(tpa)(OTf)₂, in particular the oxidation of alkenes by using hydrogen peroxide as the terminal oxidant, we have found significant differences in catalyst behavior. After several attempts it was clear that the preparative relevance of the oxidation processes was linked to the concentration of the catalyst and optimal results were obtained when the concentration value was 5 mol %. At that concentration, the Fe(bpmen)(OTf)₂ catalyst mostly gave rise to mixtures of the epoxide and the trans-dihydroxylation products formed by water-assisted hydrolytic cleavage of the epoxides. Furthermore, the use of the tripodal ligand tpa led to cis dihydroxylation products. When deactivated olefins were used as substrates for the oxidation reaction, the cis-diols were obtained exclusively, although with modest conversions, regardless of the catalyst used.     

Synthesis of indoles via palladium-catalyzed C-H activation of N-aryl amides followed by coupling with alkynes

A convenient and efficient method for the construction of indole skeleton was developed via Pd-catalyzed C-H activation of N-aryl amides and subsequent coupling with alkynes. Both stoichiometric and catalytic versions have been successfully achieved.     

Efficient synthesis of cis-2,6-di-(2-quinolylpiperidine)

An efficient synthesis of cis-2,6-di-(2-quinolylpiperidine) has been developed. The key steps involve Wittig reaction of N-Cbz-protected cis-piperidine-2,6-dicarboxaldehyde (3) with 2-(triphenylphosphinyl-methyl)quinoline bromide (4) and sequential removal of the N-Cbz group and double bond reduction. This synthetic procedure provides an efficient preparation for this useful norlobelane analogue.     

Alkyl and dialkylammonium tetrafluoroborate catalyzed cis-trans isomerization of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane

Alkyl and dialkylammonium tetrafluoroborate promoted cis-trans isomerization of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane (1) in DMSO-d₆ were studied. The isomerization equilibrium constant K are within the range of 3.74-3.30 from 22 to 47 °C. Thermodynamic parameters of ΔH° and ΔS° for the isomerization were −0.95 kcal/mol and −0.59 cal/mol-K respectively. The isomerization rate is first order in [cis-1] and second order in [R_nNH_4−nBF₄]. Both components of R_nNH_4−n⁺ and BF₄⁻ are essential for the catalytic cis-trans isomerization. The catalytic strength follows the decreasing order of ⁺H₃N(CH₂)₆NH₃⁺>n-C₈H₁₇NH₃⁺>n-C₁₆H₃₃NH₃⁺>Me₃CNH₃⁺>PhCH₂NH₃⁺>Et₂NH₂⁺?Ph₂CHNH₃⁺, Et₃NH⁺. Inversion region was observed in the plot of ln(k_f/T) versus (1/T) with the ceiling located at around 38 °C. The positive activation enthalpy of 9 kcal/mol was estimated at 22-32 °C. The activation enthalpy turns to be slightly negative at T>38 °C.     

PhP-PPh group bound to 1,8-positions of naphthalene: Preparation of cis isomer and synthesis of binuclear complex

A thermodynamically less stable cis isomer of 1,2-diphosphacycle was prepared from the corresponding trans isomer. Diphosphine, in which a PhP-PPh bond bridges the 1,8-positions of naphthalene, 1,2-diphenyl-1,2-dihydronaphtho[1,8-cd][1,2]diphosphole (1), was first prepared according to a previously reported method, and the trans isomer of 1 was irradiated in tetrahydrofuran with UV-vis light to reach equilibrium with cis-1 in a trans:cis ratio of 1:2. When a similar photochemical conversion was carried out using a saturated hexane solution of trans-1, cis-1 was precipitated in a good yield of 94%. The configuration of cis-1 was confirmed by X-ray analysis. Both cis- and trans-1 diphosphine ligands were used for the preparation of binuclear gold complexes. The crystal structure of (μ-cis-1)-[AuCl]₂ demonstrated that the two lone pairs of cis-1 are suitably directed for arrangement of the two gold centers in close proximity to each other. The two independent (μ-cis-1)-[AuCl]₂ molecules in the crystal were found to form a dimer through the multiple intermolecular interaction among the gold centers.     

Synthesis of (E)-alkenes via hydroindation of CC in InCl3-NaBH4 system

In InCl₃-NaBH₄-MeCN system, terminal aryl alkynes could couple with aryl iodides and bromides to give disubstituted alkenes via hydroindation of CC. In the similar way, (E)-alkenylsilanes were synthesized via reduction of alkynylsilanes in tetrahydrofuran (THF) in high yields. The processes showed high regio- and stereoselectivity.