Ruthenium-catalyzed hydration of nitriles and transformation of δ-ketonitriles to ene-lactams: total synthesis of (−)-pumiliotoxin C

Ag-embedded manganese oxide octahedral molecular sieve (Ag-OMS-2) nano-rods as efficient heterogeneous catalysts for hydration of nitriles to amides in aqueous solution

Silver-embedded manganese oxide octahedral molecular sieve (Ag-OMS-2) nano-rods were synthesized using a pre-incorporation approach, and unambiguously characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). A highly uniform distribution of Ag nanoparticles embedded in the porous structure of OMS-2, was found to be in favor of high catalytic activity of the composite for hydration of nitriles to corresponding amides in aqueous solution. By using a catalyst dosage of 30 mg per mmol of substrate, in the temperature range of 80-100 °C, and reaction times of 4-9 h, excellent yields (73-96%) of the desired amides (13 examples) were obtained. Also, the catalyst was easy to recycle, and showed a slight decrease in efficiency after six consecutive runs.

Stereochemical editing logic powered by the epimerization of unactivated tertiary stereocenters

The stereoselective synthesis of complex targets requires the precise orchestration of chemical transformations that simultaneously establish the connectivity and spatial orientation of desired bonds. In this work, we describe a complementary paradigm for the synthesis of chiral molecules and their isomers, which tunes the three-dimensional structure of a molecule at a late stage. Key to the success of this strategy is the development of a mild and highly general photocatalytic method composed of decatungstate polyanion and disulfide cocatalysts, which enable the interconversion of unactivated tertiary stereogenic centers that were previously configurationally fixed. We showcase the versatility of this method-and the implementation of stereoediting logic-by the rapid construction of chiral scaffolds that would be challenging to access using existing tools and by the late-stage stereoediting of complex targets.

Ru(ii)- and Ru(iv)-dmso complexes catalyze efficient and selective aqueous-phase nitrile hydration reactions under mild conditions

Synthesis and characterization of new water-soluble Ru(ii)- and Ru(iv)-dmso complexes are reported which show good efficiency and selectivity for aqueous-phase nitrile hydration at 60 °C in air. Best performance is achieved using complex [RuCl2(dmso)3(NH3)]·PF6·Cl (3).

Cyclic enaminones. Part II: applications as versatile intermediates in alkaloid synthesis

Among many other strategies, the enaminone approach is an important strategy to construct and diversify the azacyclic core in various alkaloids syntheses. In this brief review we discuss the application of cyclic enaminones as building blocks, as well as potential intermediates in the total synthesis of selected alkaloids.

Recent applications of the hetero Diels–Alder reaction in the total synthesis of natural products

The synthetic utility and potential power of the Diels–Alder (D–A) reaction in organic chemistry is evident.

Polyamide Synthesis from 6-Aminocapronitrile, Part 1:N-Alkyl Amide Formation by Amine Amidation of a Hydrolyzed Nitrile

The synthesis of N-hexylpentanamide from a stoichiometric amount of pentanenitrile and hexylamine has been studied as a model reaction for the synthesis of nylon-6 from 6-aminocapronitrile. The reaction was carried out under mild hydrothermal conditions and in the presence of a homogeneous ruthenium catalyst. For the mild hydrothermal conditions the presence of hexylamine distinctively increases the nitrile hydrolysis compared to the nitrile hydrolysis in the absence of hexylamine. Amine-catalyzed nitrile hydrolysis mainly produces the N-substituted amide. A clear product development is observed, consisting of first the terminal amide formation and second the accumulation of N-hexylpentanamide. With a maximum conversion of only 80 % after 18 h, the nitrile hydrolysis rate at 230 degrees C is still much too low for nylon-6 synthesis. Ruthenium dihydride phosphine was therefore used as a homogeneous catalyst, which significantly increases the nitrile hydrolysis rate. At a temperature of 140 degrees C and with only 0.5 mol % [RuH(2)(PPh(3))(4)] a 60 % nitrile conversion is already reached within 2 h. Initially the terminal amide is the sole product, which is gradually converted into N-hexylpentanamide. The reaction has a high initial rate, however, for higher conversions a strong decrease in hydrolysis rate is observed. This is ascribed to product inhibition, which results from the equilibrium nature of the reaction.

3-Aryl β-carbolin-1-ones as a new class of potent inhibitors of tumor cell proliferation: synthesis and biological evaluation

A novel three-step synthesis of 3-aryl beta-carbolin-1-ones from non-indole starting materials has been developed. The two nitrogen atoms in beta-carbolin-1-one were introduced efficiently by Michael addition of ethyl acetamidocyanoacetate to chalcone. The desired pyridone and indole rings were assembled by an intramolecular ketone-nitrile annulation mediated by aqueous HCl-HOAc and a Cu(I)-catalyzed intramolecular N-arylation of the amide, respectively. The target compounds were found to possess significant activity against tumor cell proliferation.

Zinc(II)/ketoxime system as a simple and efficient catalyst for hydrolysis of organonitriles

The hydrolysis of sterically hindered and unhindered alkyl nitriles, and also of benzyl and phenyl nitriles RCN (R = Me, CH(2)Cl, Et, n-Pr, i-Pr, n-Bu, t-Bu, p-MeOC(6)H(4)CH(2), Ph), to carboxamides is catalyzed by a novel system of superior simplicity consisting of cheap, widely commercially available, and rather environmentally friendly compounds, that is, a ZnX(2)/ketoxime combination, but it does not proceed at all with either the zinc salt or the ketoxime taken alone. The nature of the anion X(-) in the zinc salt (X = NO(3), Cl, CF(3)SO(3)) or of the ketoxime (Me(2)C=NOH, C(4)H(8)C=NOH, C(5)H(10)C=NOH) does not affect strongly the catalytic properties of the system, but the best results were obtained so far with a Zn(NO(3))(2).6H(2)O/2-propanone oxime molar ratio of 1:4; turnover numbers are typically above ca. 100 but reach as high as 1000 for p-MeOC(6)H(4)CH(2)C(=O)NH(2). The previously unknown structures of the two carboxamide products n-BuC(=O)NH(2) and p-MeOC(6)H(4)CH(2)C(=O)NH(2) were determined by X-ray diffraction studies. The complexes [ZnX(2)(R(2)C=NOH)(2)] (X = Cl, R(2) = 2Me, C(4)H(8), C(5)H(10); X = NO(3), R = C(4)H(8)), prepared by heating the appropriate zinc salts with 2 equiv of the ketoxime in acetone and characterized by C, H, N analyses, FAB-MS, (1)H and (13)C[(1)H] NMR spectroscopies, and also X-ray crystallography (for X = Cl, R(2) = 2Me; X = NO(3), R = C(4)H(8)), proved to be catalyst precursors in the conversions because the activity of these species is high only in the presence of 2 equiv of the ketoxime.

Stereodivergent process for the synthesis of the decahydroquinoline type of dendrobatid alkaloids

A flexible and stereodivergent synthesis of the cis- and trans-fused 2,5-disubstituted octahydroquinolinone ring systems bearing all four stereogenic centers for the synthesis of the decahydroquinoline type of dendrobatid alkaloids has been achieved. The strategy involves stereoselective and stereodivergent construction of 2,3,6-trisubstituted piperidine ring systems using the Michael type of conjugate addition reaction to the enaminoesters 1 and 3, the intramolecular aldol type of cyclization reaction of keto aldehydes 11 and 12, and ring-closing metathesis of 21 as key steps.

Solid-phase synthesis of 1,2,3,4-tetrahydro-2-pyridones via aza-annulation of enamines

An efficient solid-phase approach has been developed to prepare nitrogen heterocycles with a 1,2,3,4-tetrahydro-2-pyridone core via aza-annulation of enamines. Immobilized enamines were prepared from the reaction of primary amines with propynoic acid derivatives or ketones. Aza-annulation reactions were carried out by reacting resin-bound enamines with symmetrical alpha,beta-unsaturated acid anhydrides or alpha,beta-unsaturated acids in the presence of DPPA and TEA. The annulation products were isolated in good to high crude yields. Influence of sterically hindered amines as well as alpha- and beta-substituted acrylic acid derivatives on the annulation reaction was also investigated.

Using the Pummerer cyclization-deprotonation-cycloaddition cascade of imidosulfoxides for alkaloid synthesis

The Pummerer reaction of imidosulfoxides bearing tethered alkenyl groups has been employed for the synthesis of several alkaloids. The required imidosulfoxides necessary for the cascade sequence were easily obtained by heating the appropriate amide with (ethylsulfeny)acetyl chloride followed by sodium periodate oxidation. The initially formed thionium ion, obtained by treating the imidosulfoxide with acetic anhydride and p-toluenesulfonic acid, reacts with the neighboring imido group, and the resulting oxonium ion undergoes subsequent deprotonation to produce an isomünchnone dipole. This mesoionic betaine intermediate undergoes ready intramolecular dipolar cycloaddition across the neighboring pi-bond. Exposure of the resulting cycloadducts to additional acetic anhydride leads to ring opening and formation of a 5-acetoxy-substituted 2(1H)-pyridone. This six-ring heterocyclic system constitutes a valuable building block for the synthesis of a variety of pyridine, quinolizidine, and clavine alkaloids. The cyclization-deprotonation-cycloaddition cascade has been successfully applied to the synthesis of the naturally occurring alkaloids onychnine, dielsiquinone, (+/-)-lupinine, (+/-)-anagyrine, (+/-)-pumiliotoxin C, and (+/-)-costaclavine.