Stereoselective halogenation is a highly useful organic transformation for multistep syntheses because the resulting chiral organohalides can serve as precursors for various medicinally relevant ...derivatives. Even though decarboxylative halogenation of aliphatic carboxylic acids is a useful and fundamental synthetic method for the preparation of a variety of organohalides, an enantioselective version of this reaction has not been reported. Here we report a highly enantioselective decarboxylative chlorination of β-ketocarboxylic acids to obtain α-chloroketones under mild organocatalytic conditions. The present method is also applicable for the enantioselective synthesis of tertiary α-chloroketones. The conversions of the resulting α-chloroketones into α-aminoketones and α-thio-substituted ketones via S
2 reactions at the tertiary carbon centres are also demonstrated. These results constitute an efficient approach for the synthesis of chiral organohalides and are expected to enhance the availability of enantiomerically enriched chiral compounds with heteroatom-substituted chiral stereogenic centres.
The highly enantioselective fluorination of α-branched aldehydes was achieved using newly developed chiral primary amine catalyst
. Furthermore, the C-F bond cleavage of the resulting ...α-fluoroaldehydes proceeded smoothly under alcoholic alkaline conditions to yield the corresponding α-hydroxyacetals in a stereospecific manner. Accordingly, the one-pot conversion of α-branched aldehydes into α-hydroxyacetals was achieved for the first time in high enantioselectivity.
The highly enantioselective fluorination of α-branched aldehydes was achieved using newly developed chiral primary amine catalyst
1
. Furthermore, the C-F bond cleavage of the resulting ...α-fluoroaldehydes proceeded smoothly under alcoholic alkaline conditions to yield the corresponding α-hydroxyacetals in a stereospecific manner. Accordingly, the one-pot conversion of α-branched aldehydes into α-hydroxyacetals was achieved for the first time in high enantioselectivity.
The highly enantioselective fluorination of α-branched aldehydes was achieved using newly developed chiral primary amine catalyst.
The highly enantioselective fluorination of α-branched aldehydes was achieved using newly developed chiral primary amine catalyst.
The highly enantioselective fluorination of α-branched aldehydes was ...achieved using newly developed chiral primary amine catalyst
1
. Furthermore, the C–F bond cleavage of the resulting α-fluoroaldehydes proceeded smoothly under alcoholic alkaline conditions to yield the corresponding α-hydroxyacetals in a stereospecific manner. Accordingly, the one-pot conversion of α-branched aldehydes into α-hydroxyacetals was achieved for the first time in high enantioselectivity.
Stereoselective halogenation is a highly useful organic transformation for multistep syntheses because the resulting chiral organohalides can serve as precursors for various medicinally relevant ...derivatives. Even though decarboxylative halogenation of aliphatic carboxylic acids is a useful and fundamental synthetic method for the preparation of a variety of organohalides, an enantioselective version of this reaction has not been reported. Here we report a highly enantioselective decarboxylative chlorination of β-ketocarboxylic acids to obtain α-chloroketones under mild organocatalytic conditions. The present method is also applicable for the enantioselective synthesis of tertiary α-chloroketones. The conversions of the resulting α-chloroketones into α-aminoketones and α-thio-substituted ketones via SN 2 reactions at the tertiary carbon centres are also demonstrated. These results constitute an efficient approach for the synthesis of chiral organohalides and are expected to enhance the availability of enantiomerically enriched chiral compounds with heteroatom-substituted chiral stereogenic centres.
•The measurement of the Debye temperature of pyrite-type PdSb2.•The usefulness of the single crystal X-ray diffraction method.•Systematic variations in the Debye temperatures and the M-X distances.
...Single crystals of pyrite-type PdSb2 were grown by sealing a stoichiometric proportion of the elements in an evacuated silica glass tube and heating the tube in a furnace at 930 K for 20 days. The crystal structure of PdSb2 space groupPa3¯, a = 6.4659(2) Å, u = 0.37331(3), Z = 4 was refined to R1 = 0.0171 for 374 unique reflections obtained by single-crystal X-ray diffraction experiments. The lattice constant, a, and anion-anion distance of 2.8677(3) Å are slightly different from the previously reported values. The single crystal diffraction method has excellent advantages such that the Debye temperature can be determined for each crystallographically independent site. The obtained ΘD values for Pd and Sb in PdSb2 are 258 K and 214 K, respectively. Characteristically, the Debye temperatures, ΘD, of both atoms in PdSb2 were found to be very low among the pyrite-type transition metal pnictides and chalcogenides. Certain regularities between the cation–anion bonding distances and Debye temperatures were found in pyrite-type compounds. The vibration of anion contributes to the highest energy part of the normal mode of thermal vibration, when the cation–anion bonding distances in pyrite-type compounds are shorter than 2.6 Å.
Single crystals of Ni3Se2 (trinickel diselenide) and NiSe (nickel selenide) with stoichiometric chemical compositions were grown in evacuated silica‐glass tubes. The chemical compositions of the ...single crystals of Ni3Se2 and NiSe were determined by scanning electron microscopy and energy‐dispersive X‐ray spectroscopy (SEM/EDS). The crystal structures of Ni3Se2 rhombohedral, space group R32, a = 6.02813 (13), c = 7.24883 (16) Å, Z = 3 and NiSe hexagonal, space group P63/mmc, a = 3.66147 (10), c = 5.35766 (16) Å, Z = 2 were analyzed by single‐crystal X‐ray diffraction and refined to yield R values of 0.020 and 0.018 for 117 and 85 unique reflections, respectively, with Fo > 4σ(Fo). R32 is a Sohncke type of space group where enantiomeric structures can exist; the single‐domain structure obtained by the refinement was confirmed to be correct by a Flack parameter of −0.05 (2). The existence of Ni—Ni bonds was confirmed in both compounds, in addition to the Ni—Se bonds. The value of the atomic displacement parameter (mean‐square displacement) of each atom in NiSe was larger than that in Ni3Se2. The larger amplitude of the atoms in NiSe corresponds to longer Ni—Se and Ni—Ni bond lengths in NiSe than in Ni3Se2. The Debye temperatures, gθD, estimated from observed mean‐square displacements for Ni and Se in Ni3Se2, were 322 and 298 K, respectively, while those for Ni and Se in NiSe were 246 and 241 K, respectively. The existence of large cavities in the structure and the weak bonding force are likely responsible for the brittle and soft nature of the NiSe crystal.
Single‐crystal X‐ray diffraction investigation of the single‐domain structures of stoichiometric Ni3Se2 and NiSe are reported.
Abstract Background Three-dimensional quantitative coronary angiography (3D-QCA) reportedly allows more accurate delineation of true vessel geometry when compared with standard two-dimensional (2D) ...QCA and has been validated by intravascular ultrasound (IVUS). This study sought to compare diagnostic efficiency of 2D- and 3D-QCA, and IVUS in identifying hemodynamically significant coronary stenoses as determined by fractional flow reserve (FFR). Methods Forty-two lesions in 40 patients were assessed by FFR, IVUS, and 2D- and 3D-QCA. Correlations between FFR values and anatomical parameters obtained by 2D- and 3D-QCA and IVUS were analyzed. The receiver operating characteristic (ROC) curves were used to compare the diagnostic accuracy of the parameters for predicting FFR ≤ 0.80. Results Mean FFR value was 0.75 ± 0.13. FFR ≤ 0.80 was observed in 28 lesions (67%). Of IVUS measurements, minimum lumen area (MLA) well correlated with FFR values ( r = 0.71, p < 0.001). Of 3D- and 2D-QCA measurements, minimum lumen diameter (MLD) correlated best with FFR values ( r = 0.79, p < 0.01; r = 0.68, p < 0.01, respectively), followed by MLA ( r = 0.76, p < 0.01; r = 0.67, p < 0.01, respectively). The area under the ROC curve for 3D-QCA MLD was greater than those for 2D-QCA MLD ( p = 0.03) and 2D-QCA MLA ( p = 0.03). On the other hand, the AUC for 3D-QCA MLD, 3D-QCA MLA, and IVUS MLA were not significantly different. Conclusions 3D-QCA is more useful than 2D-QCA and possibly comparable to IVUS in the assessment of functional stenosis severity. When FFR is not available, 3D-QCA MLA and MLD may assist in the assessment of functional severity of intermediate lesions.
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