Asymmetric Rubottom-Type Oxidation Catalyzed by Chiral Calcium Phosphates.

Invited for the cover of this issue is the group of Jon C. Antilla at Zhejiang Sci-Tech University. The image depicts asymmetric Rubottom-type oxidation catalyzed by chiral calcium phosphates. Read the full text of the article at 10.1002/chem.202203720.

Asymmetric Rubottom-Type Oxidation Catalyzed by Chiral Calcium Phosphates.

A highly efficient catalytic asymmetric Rubottom-type oxidation is described. Using meta-chloroperbenzoic acid (m-CPBA) as the oxidant and chiral calcium phosphate as the catalyst, the facile transformation enables direct hydroxylation of N-Boc oxindoles and ß-ketoesters in high yields (up to 99 %) and in a highly enantioenriched fashion (up to >99 % ee). The application of the established method was demonstrated by the synthesis of a pharmaceutically important 3-hydroxyoxindole with excellent enantiocontrol.

Chiral Calcium Phosphate-Catalyzed Enantioselective Amination of 3-Aryl-2-oxindoles with Dibenzyl Azodicarboxylate.

A chiral calcium phosphate-catalyzed enantioselective amination of 2-oxindoles with dibenzyl azodicarboxylate has been developed, affording the products in consistently high yields and excellent enantioselectivity. This synthetic method features low catalyst loading and a high catalytic efficiency. Moreover, the practical value of this process is well demonstrated by a scale-up experiment and a trial of catalyst recovery and reuse.

Enantioselective Amination of ß-Keto Esters Catalyzed by Chiral Calcium Phosphates.

A catalytic enantioselective amination of ß-keto esters using (S)-BINOL chiral calcium phosphate has been developed. The reaction produces chiral α-amino-ß-keto ester derivatives in most cases with moderate to excellent enantioselectivities (up to 99 %) and good yields (up to 99 %). This mild synthetic method highlights a low catalyst loading and high catalytic efficiency. When the substrate backbone was changed to 1-tetralone-derived ß-keto esters, unexpectedly high yields of selective redox products were obtained. The practicality of the reaction was realized by a scale-up without any significant loss in the enantioselectivity and yield. Chiral calcium phosphate was successfully recovered and reused for four runs, indicating its stability and high catalytic activity.

Chiral Calcium Phosphate Catalyzed Enantioselective Amination of 3-Aryl-2-benzofuranones.

A 4-tert-butyl-phenyl substituted (R)-[H8]-BINOL chiral calcium phosphate catalyzed enantioselective amination of 3-aryl-2-benzofuranones with dibenzyl azodicarboxylate is described. The catalyst loading of the reaction is 1 mol %. This transformation is facile and has a high degree atom economy, which gave products with good yields and high enantioselectivities (79% to 99%). This reaction has excellent ee and a broad substrate scope with mild reaction conditions.

Crystal structure of benzyl 3-oxo-2-oxa-5-aza-bicyclo-[2.2.1]heptane-5-carboxyl-ate.

The title compound, C13H13NO4 (also known as N-benzyl-oxycarbonyl-4-hy-droxy-l-proline lactone), crystallizes with two mol-ecules in the asymmetric unit. They have slightly different conformations: the fused ring systems almost overlap, but different C-O-C-C torsion angles for the central chains of -155.5 (2) and -178.6 (2)° lead to different twists for the terminal benzene ring. In the crystal, the mol-ecules are linked by C-H⋯O inter-actions, generating a three-dimensional network. The absolute structure was established based on an unchanging chiral centre in the synthesis.

Crystal structure of (1R,4R)-tert-butyl 3-oxo-2-oxa-5-aza-bicyclo-[2.2.2]octane-5-carboxyl-ate.

In the title compound, C11H17NO4, commonly known as N-tert-but-oxy-carbonyl-5-hy-droxy-d-pipecolic acid lactone, the absolute configuration is (1R,4R) due to the enantiomeric purity of the starting material which remains unchanged during the course of the reaction. In the crystal there no inter-molecular hydrogen bonds.

Crystal structure of (tert-butyl-carbamo-yl)(4-chloro-2-oxo-2H-chromen-3-yl)methyl acetate.

In the title compound, C17H18ClNO5, which was synthesized by reacting 4-chloro-3-formyl-coumarin, acetic acid and tert-butyl isocyanide, the acetamido side chain is convoluted with ring-to-side chain C-C-C-C, C-C-C-N and C-C-N-C torsion angles of -123.30 (14), -135.73 (12) and 176.10 (12)°, respectively. In the crystal, N-H⋯O and weak C-H⋯O hydrogen bonds are present, which together with π-π coumarin-ring inter-actions [ring centroid separations = 3.4582 (8) and 3.6421 (9) Å], give rise to a layered structure lying parallel to (001).

Crystal structure of 3,4-dimethyl 2-(tert-butyl-amino)-5-[2-oxo-4-(thio-morpholin-4-yl)-2H-chromen-3-yl]furan-3,4-di-carboxyl-ate ethyl acetate hemisolvate.

In the title hemisolvate, C25H28N2O7S·0.5C4H8O2, the thio-morpholine ring adopts a chair conformation, with the exocyclic N-C bond in an equatorial orientation. The dihedral angle between the coumarin ring system (r.m.s. deviation = 0.044 Å) and the furan ring is 64.84 (6)°. An intra-molecular N-H⋯O hydrogen bond closes an S(6) ring. The ethyl acetate solvent mol-ecule is disordered about a crystallographic inversion centre. In the crystal, the components are linked by C-H⋯O and C-H⋯S hydrogen bonds, generating a three-dimensional network.

Crystal structure of ethyl 2-(2-{1-[N-(4-bromo-phen-yl)-2-oxo-2-phenyl-acetamido]-2-tert-butyl-amino-2-oxo-ethyl}-1H-pyrrol-1-yl)acetate.

In the title compound, C28H30BrN3O5, there is an intra-molecular N-H⋯O hydrogen bond and an intra-molecular C-H⋯O hydrogen bond, both forming S(9) ring motifs. The planes of the 4-bromo-phenyl ring and the phenyl ring are inclined to that of the pyrrole ring by 48.05 (12) and 77.45 (14)°, respectively, and to one another by 56.25 (12)°. In the crystal, mol-ecules are linked via C-H⋯O hydrogen bonds and C-H⋯π inter-actions, forming slabs parallel to (10-1).

Mutually ordered self-assembly of discotic liquid crystal-graphene nanocomposites.

The room temperature anthraquinone discotic 1,5-dihydroxy-2,3,6,7-tetrakis(3,7-dimethyloctyloxy)-9,10-anthraquinone (RTAQ) self-assembles in the presence of octadecylamine functionalized graphene (f-graphene) into an ordered sandwich like structure, where the discotic molecules form columnar structures on graphene sheets. Cryo-SEM and SEM images provide evidence for this ordering. This behaviour is also supported by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and conductivity studies of nanocomposites.