Catalytic asymmetric hydrogenations of prochiral unsaturated compounds, 1 olefin, 2 ketone, 3 and imine, 4 have been intensively studied and are considered as a versatile method of creating a chiral carbon center. 5 However, no highly enantioselective hydrogenation of heteroaromatic groups has so far been reported except that of 2-methylquinoxaline to our knowledge. 6 Resonance stability of heteroaromatic compounds might impede the enantioselective hydrogenation, 7 which may find potentially wide applicability in stereoselective organic synthesis. 8,9 Herein, we describe the highly enantioselective hydrogenation of heteroaromatic compounds, indoles.We recently disclosed that the rhodium complex generated from Rh(acac)(cod) and PPh 3 is a good catalyst for the hydrogenation of five-membered heteroaromatic compounds. 10 Thus chiral rhodium complexes prepared in situ from Rh(acac)(cod) and various commercially available chiral bisphosphines (1 mol %) were examined for asymmetric hydrogenation of N-acetyl-2-butylindole (1a) at 60°C for 2 h with 5.0 MPa of H 2 in 2-propanol (eq 1), resulting in non-enantioselective hydrogenation (0-1% ee). 11 Fortunately, the successful asymmetric hydrogenation has been achieved by use of a trans-chelating chiral bisphosphine ligand, (S,S)-(R,R)-PhTRAP, 12,13 giving (R)-N-acetyl-2-butylindoline (2a) with 85% ee (77% conversion). No reduction of the fused aromatic ring of 1a was observed.On further investigation into the asymmetric hydrogenation, [Rh(nbd) 2 ]SbF 6 was found to be superior to Rh(acac)(cod) as catalyst precursor (Table 1). It is noted that addition of base is necessary for achievement of high enantioselectivity as well as high catalytic activity. The [Rh(nbd) 2 ]SbF 6 -(S,S)-(R,R)-PhTRAP catalyst scarcely promoted the hydrogenation in the absence of base, giving a trace of 2a with only 7% ee (S) (entry 1). Addition of 10 mol % of Et 3 N or Cs 2 CO 3 brought remarkable improvement of the enantioselectivity and catalytic activity (100% conversion, 94% ee (R)) (entries 2 and 3). 14 Both the enantioselectivity and catalytic activity were significantly dependent upon base: K 2 -CO 3 gave (R)-2a with 76% ee, and pyridine did not activate the cationic PhTRAP-rhodium complex at all (entries 4 and 5). The amount of Cs 2 CO 3 did not affect the selectivity: 20 mol %, 94% ee; 1 mol %, 93% ee. It is possible to carry out the asymmetric hydrogenation at lower pressure (1.0 MPa) without significant decrease of the selectivity and reaction rate (entry 6). The amount of PhTRAP-rhodium complex can be reduced to 0.1 mol %, and the reaction was completed within 20 h to give (R)-2a of 93% ee in 92% isolated yield (entry 7).Although 2-propanol has frequently been used as a hydrogen source in the transfer hydrogenation of unsaturated compounds (1) For reviews, see: (a) Takaya, H.; Ohta, T.; Noyori, R. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.; VCH Publishers: New York
We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the dayside of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2 m Subaru telescope. The telluric and stellar lines are removed using a detrending algorithm, SysRem. The residuals are then cross-correlated with OH and H2O planetary spectrum templates produced using several different line lists. We check and confirm the accuracy of OH line lists by cross-correlating with the spectrum of GJ 436. As a result, we detect the emission signature of OH at K p of km s−1 and v sys of −0.3 km s−1 with a signal-to-noise ratio (S/N) of 5.4 and a significance of 5.5σ. Additionally, we marginally detect H2O emission in the H-band with an S/N of 4.0 and a significance of 5.2σ using the POKAZATEL line list. However, no significant signal is detected using the HITEMP 2010, which might be due to differences in line positions and strengths, as well as the incompleteness of the line lists. Nonetheless, this marginal detection is consistent with the prediction that H2O is mostly thermally dissociated in the upper atmosphere of the ultra-hot Jupiters. Therefore, along with CO, OH is expected to be one of the most abundant O-bearing molecules in the dayside atmosphere of ultra-hot Jupiters and should be considered when studying their atmospheres.
We obtained spectra of the pre-main-sequence star AU Microscopii during a transit of its Neptune-sized planet to investigate its orbit and atmosphere. We used the high-dispersion near-infrared spectrograph InfraRed Doppler (IRD) on the Subaru telescope to detect the Doppler “shadow” from the planet and constrain the projected stellar obliquity. Modeling of the observed planetary Doppler shadow suggests a spin–orbit alignment of the system ( deg), but additional observations are needed to confirm this finding. We use both the IRD data and spectra obtained with NIRSPEC on Keck II to search for absorption in the 1083 nm line of metastable triplet He i by the planet’s atmosphere and place an upper limit for the equivalent width of 3.7 mÅ at 99% confidence. With this limit and a Parker wind model we constrain the escape rate from the atmosphere to M ⊕ Gyr−1, comparable to the rates predicted by an X-ray and ultraviolet energy-limited escape calculation and hydrodynamic models, but refinement of the planet mass is needed for rigorous tests.
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