Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Nitroarenes are the entry point for the production of most nitrogen-containing aromatic compounds. Thus, any transformation that leads directly from them to the final product allows saving one or more synthetic steps. This review deals with homogeneously catalyzed reactions leading to the formation of N-heterocyclic compounds from nitroarenes or nitroalkenes in one pot. Reactions that lead to the intermediate formation of amines are not considered. Carbon monoxide is the most often employed reductant because it allows selective reactions, is cheap, and only produces CO2 as stoichiometric byproduct. However, the difficulty in handling pressurized CO has stimulated in recent years the development of CO-surrogates, that is molecules able to liberate CO during the reaction. The use of phosphines and diols has also been developed in conjunction with molybdenum catalysts. The review focusses in more detail on the literature in the period 2006\u20132018, but reference to earlier work is made when necessary to put recent results in a more general context

Palladium-Catalyzed Intramolecular Cyclization of Nitroalkenes : Synthesis of Thienopyrroles

In the presence of carbon monoxide, the palladium/phenanthroline system catalyzes the intramolecular amination of thiophene rings following the reduction of a nitroalkene moiety directly attached to the S-heterocyclic ring. Optimization of the ligand and reaction conditions allowed the synthesis of a series of thienopyrroles aryl/alkyl-substituted at either the 2- or 3-position of the pyrrole ring. By using low pressures of carbon monoxide (5 bars), high yields of fused bicyclic compounds have been obtained (up to 98 % yield)

The beneficial influence of ultrasound in the polymerization of ε-caprolactam to polyamide-6 (Nylon 6). Part I: Primary experimental results

Epsilon-caprolactam (CL) polymerization to polyamide-6 (Nylon 6) was studied at different contents of water in CL (0.01-2 wt%), with or without epsilon-amino-caproic acid (ACA) as an activator, applying to the mixture an initial treatment of Ultrasound (US) (17.5-20 kHz) at low temperatures (70-110 degrees C) and for short times (max 10 min). It was verified that polymerization at 260 degrees C produces a polymer having a much higher molecular weight (MW) when US is applied with respect to silent (SIL) conditions i.e. without the use of ultrasound. This constitutes a "pre-sonication effect". The ratio (MW)(US)/(MW)(SIL) is inversely proportional to the initial content of water in CL. The action of US converts CL at very low temperatures (70-110 degrees C) and water content, in comparison with silent conditions where CL was unconverted. Optimized conditions are studied with respect to nature and pressure of gas inside the reactor, temperature, time and frequency of US irradiation, energy consumption and nature of activator

Use of amido Grignard reagents in inorganic chemistry : Synthesis and crystal structure of anti-[Pd(Cl)(py)(mu-2,6-Pri2C6H3NH)](2)

Treating a pyridine (py) solution of PdCl2(py)(2) with a tetrahydrofuran or diethyl ether solution of the amido Grignard reagent 2,6-(Pr2C6H3NH)-C-1(MgCl) afforded a dimeric palladium complex, containing two bridging amido groups, which has been structurally characterised

The double RGB in M 2: C, N, Sr and Ba abundances

The globular cluster M 2 has a photometrically detected double red giant branch (RGB) sequence. We investigate here the chemical differences between the two RGBs in order to gain insight in the star formation history of this cluster. The low-resolution spectra, covering the blue spectral range, were collected with the MODS spectrograph on the LBT, and analyzed via spectrum synthesis technique. The high quality of the spectra allows us to measure C, N, Ba, and Sr abundances relative to iron for 15 RGB stars distributed along the two sequences. We add to the MODS sample C and N measurements for 35 additional stars belonging to the blue RGB sequence, presented in Lardo et al. (2012). We find a clear separation between the two groups of stars in s-process elements as well as C and N content. Both groups display a C-N anti-correlation and the red RGB stars are on average richer in C and N with respect to the blue RGB. Our results reinforce the suggestion that M2 belongs to the family of globular clusters with complex star formation history, together with Omega Cen, NGC 1851, and M 22.Comment: 11 pages, 8 figures. Accepted for publication in MNRA

Synthesis of Oxazines by Palladium Catalyzed Reductive Cyclization of Nitroarenes and Dienes Using Phenyl Formate as CO Surrogate

The synthesis of hetero-Diels-Alder adducts derived from nitrosoarenes as dienophiles (oxazines) has been the focus of much attention in recent years, since these products have pharmacological activity themselves or can be easily transformed into other products. 1 However, their usual synthesis requires problematic intermediate isolation of nitroso compounds. We have previously reported a method for oxazines synthesis in up to 91% yields in one pot by the reaction of unfunctionalized dienes with nitroarenes and carbon monoxide.2 Despite the high efficiency of this synthetic procedure, it has not become of widespread use by the chemical community. This is mostly because it involves the use of pressurized CO, requiring safety measures that are not available in most synthetic organic laboratories. To overcome this limitation, we started investigating the use of molecules capable of releasing CO in situ, thus avoiding the need for high-pressure equipment and CO lines. Recently, we have reported3 an efficient, convenient and general synthetic procedure to produce nitrogen heterocycles from nitro compounds in presence of a Pd catalyst employing phenyl formate as the CO releasing agent. In this study, we take advantage of this general procedure in the synthesis of oxazines from dienes and nitroarenes (Figure 1). First, due to its high cost, the amount of the diene was optimized down to 1:4 nitroarene to diene ratio. The reaction works well for nitroarenes bearing either electron-donating or electron-withdrawing substituents, a moderate steric hindrance on the nitroarene is well tolerated and yields up to 99% in one pot were reached. In addition, variation in the diene were also investigated using 2,3-dimethoxy-1,3-butadiene, isoprene and myrcene affording the corresponding oxazines in good yields