Straightforward Solvent-Free Heterogeneous Palladium-Catalyzed Synthesis of Arylamines from Nonaromatic Substrates by Dehydrogenative Alkylation

Abstract

Aldrich, Alfa Aesar and TCI. All reagents were used as received from the chemical company without further purification, excepted for aniline and nitrobenzene which were distilled prior to use. Pd/C (5%) on activated carbon, reduced and dry (Escat 1431) and all the supported catalysts were purchased from Strem Chemicals and Sigma-Aldrich.1 H NMR and 13 C NMR spectra were recorded on a BRUKER DRX 300 or BRUKER ALS 300 ( 1 H 300 MHz, 13 C 75 MHz) in CDCl 3 (except when mentioned) and chemical shifts are given in ppm. J values are given in Hertz (Hz). Abbreviations are defined as follows: br = broad singlet, s = singlet, d = doublet, dd = doublet of doublets, t = triplet, q = quadruplet, m = multiplet.IR spectra were recorded on a Spectro Nicolet IS10 Smart ITR with an ATR diamond.The HRMS-ESI mass spectra were recorded in positive-ion mode on a hybrid quadrupole time-of-flight mass spectrometer (MicroTOFQ-II, Bruker Daltonics, Bremen) with an Electrospray Ionization (ESI) ion source. The flow of spray gas was at 0.6 bar and the capillary voltage was 4.5kV. The solutions were infused at 180µL/h in a mixture of solvents (methanol / dichloromethane / water 45/40/15). The mass range of the analysis was 50-1000m/z and the calibration was done with sodium formate.The HRMS-CI (Chemical Ionization) and HRMS-EI (Electron Ionization) mass spectra were recorded on a high resolution double-focusing (reversed Nier-Johns B/E geometry) mass spectrometer (ThermoFinnigan MAT95XL, Bremen, Germany) equipped with a chemical ionization (CI) and an electron ionization (EI) ion sources. The reagent gas for the CI was isobutane and the calibration for high resolution mass spectra was done with perfluorotrybutylamine (FC43). For the EI an electron energy of 70eV was used and the calibration was done with perfluorokerozene (PFK).The GC-MS analysis were performed on a Focus GC (Thermo Electron Corporation, Bremen, Germany) equipped with a DB-5MS capillary column (30m, 0.25mm i.d, 0.25µm film thickness) and a DSQ mass spectrometer as a detector (Thermo Electron corporation, Bremen, Germany). The carrier gas was helium, at a flow rate of 1 mL/min. Column temperature was initially 70°C for 2 min, then gradually increased to 310°C at 15°C/min and finally kept at 310°C for 10min. The injector temperature was 220°C and the transfer line temperature was 280°C. For GC-MS detection an electron ionization system was used with electron energy of 70 eV, and the mass analyzer was a simple quadrupole. S3 Dehydrogenative alkylation of α-tetralone with amines (A):In a sealed tube under argon, 3 mmol of α-tetralone derivative were added to 15 mmol of amine. Next, 64 mg of Pd/C (5%) (0.03 mmol, 1 mol%) were added to the mixture, under an inert argon atmosphere. The medium was stirred at 130 °C for 16-36 h at 800 rpm, depending on the substrate. Thereafter, the crude was dissolved in a mixture of CH 2 Cl 2 and CH 3 OH and filtered off (Millipore Durapore filter 0.01 µm).The solvents were evaporated under reduced pressure and the crude product was finally purifi...

Palladium-Catalyzed Aerobic Dehydrogenation of Cyclic Hydrocarbons for the Synthesis of Substituted Aromatics and Other Unsaturated Products

“…In addition, Lemaire and co-workers showed that various cyclohexanones could be used as neat substrates to achieve dehydrogenative coupling with amines using Pd/C as the catalyst (Scheme 25C). 46 This method was typically more efficient and selective with 1-octene as a hydrogen acceptor, rather than O 2 , although tetralones underwent coupling in the absence of an acceptor to afford 1-aminonaphthalenes. Collectively, these results represent a valuable application of oxidative dehydrogenation catalysis.…”

Catalytic Aerobic Dehydrogenation of Nitrogen Heterocycles Using Heterogeneous Cobalt Oxide Supported on Nitrogen-Doped Carbon

“…2 In many cases, these methods enable synthesis of aromatic compounds with substitution patterns and/or functional groups that are difficult to access via traditional aromatic functionalization reactions. This strategy has been employed by us and others in Pd-catalyzed methods for the conversion of cyclohexanone and cyclohexenone derivatives into substituted phenols, 3 aryl ethers 4 or anilines 5 and for the conversion of cyclohexene derivatives into substituted arenes. 6 More recently, we began exploring methods for aerobic dehydrogenation of partially saturated N -heterocycles to heteroarenes.…”

“…Heterogeneous Pd catalysts have been successfully used for the dehydrogenation of cyclohexanones and cyclohexenones. 3d,e,4b,5e Other heterogeneous catalysts composed of noble metals (Ru, Au, Pd 3 Pb) have also been shown to be active for aerobic dehydrogenation of the parent 1,2,3,4-tetrahydroquinoline; 17 however, the reactions proceed at high temperatures (>100 °C), they are accompanied by catalyst deactivation, and the results were not extended to substituted tetrahydroquinoline derivatives. During the course of these initial studies, Beller and coworkers reported a unique Co-oxide-based catalyst for aerobic alcohol oxidation (oxidative esterification of primary alcohols).…”

Reductive amination using a combination of CaH2 and noble metal

“…9 Recently, amines were prepared via a hydrogen autotransfer in the presence of a metal catalyst. 21 In order to increase the selectivity of the reaction, the different parameters were modied. 12 Aer an analysis of the literature data, we were curious to notice that the calcium hydride was poorly explored for the reduction of organic functions.…”