Continuous Enantioselective α-Alkylation of Ketones via Direct Photoexcitation.

Motivated by the scarcity of enantioselective direct intermolecular α-alkylation reactions of ketones with simple alkyl halides, we report a photo-organocatalytic process to access diethyl 2-(2-oxocyclohexyl)malonate and derivatives in good yield and enantioselectivity. The reaction design is based on highly abundant and nature-derived 9-amino-9-deoxy-epi-cinchona alkaloids to activate ketones as transient secondary enamines, which exist unfavorably in equilibrium with imines. These condensed species can serve as powerful photoinitiators via direct photoexcitation. This concept provides access to both enantiomeric antipodes. In addition to introducing an uncomplicated batch-optimized procedure, we investigated the feasibility and limitations of implementing the reaction in continuous flow, thus enabling to obtain diethyl 2-(2-oxocyclohexyl)malonate with a productivity of 47 µmol/h and 84% enantioselectivity.

Ilmenite-type Na2(Fe2/3Te4/3)O6.

Na2(Fe2/3Te4/3)O6 (Z = 3) or Na3(FeTe2)O9 (Z = 2), tris-odium iron(III) ditellurium(VI) nona-oxide, adopts the ilmenite (FeTiO3, Z = 6) structure type with the Ti site (site symmetry 3.) replaced by Na and the Fe site (site symmetry 3.) replaced by a mixed-occupied (FeIII,TeVI) site in a Fe:Te ratio of 1:2. Whereas the [(Fe,Te)O6] octa-hedron is only slightly distorted, the [NaO6] octa-hedron shows much stronger distortions, as revealed by a larger spread of the bond lengths and some distortion parameters.

Construction of the Bicyclic Carbon Framework of Euphosalicin.

Our studies toward the total synthesis of the natural product euphosalicin (1) are presented. Different approaches targeting key intermediates are described, the synthesis of which includes findings on asymmetric dihydroxylations and ring-closing enyne metatheses (RCEYM). Their connection allowed the isolation of highly advanced precursors for studies on macrocyclizations. Our efforts culminated in the preparation of the unique C11/C12 (Z) isomer of the C13 nor methyl skeleton of euphosalicin (1).

Synthesis and crystal structure of (NH4)[Ni3(HAsO4)(AsO4)(OH)2].

The title compound, ammonium trinickel(II) hydrogen arsenate arsenate di-hydroxide, was synthesized under hydro-thermal conditions. Its crystal structure is isotypic with that of K[Cu3(HAsO4)(AsO4)(OH)2] and is characterized by pseudo-hexa-gonal (001) 2 ∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers formed from vertex- and edge-sharing [NiO4(OH)2] octa-hedra and [AsO3.5(OH)0.5] tetra-hedra as the building units. The hydrogen atom of the OH group shows occupational disorder and was refined with a site occupation factor of 1/2, indicating the equal presence of [HAsO4]2- and [AsO4]3- groups. Strong asymmetric hydrogen bonds between symmetry-related (O,OH) groups of the arsenate units [O⋯O = 2.588 (18) Å] as well as hydrogen bonds accepted by these (O,OH) groups from OH groups bonded to the NiII atoms [O⋯O = 2.848 (12) Å] link adjacent layers. Additional consolidation of the packing is achieved through N-H⋯O hydrogen bonds from the ammonium ion, which is sandwiched between adjacent layers [N⋯O = 2.930 (7) Å] although the H atoms could not be located in the present study. The presence of the pseudo-hexa-gonal 2 ∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers may be the reason for the systematic threefold twinning of (NH4)[Ni3(HAsO4)(AsO4)(OH)2] crystals. Significant overlaps of the reflections of the respective twin domains complicated the structure solution and refinement.

Cadmium phosphates Cd2(PO4)OH and Cd5(PO4)2(OH)4 crystallizing in mineral structures.

Single crystals of two basic cadmium phosphates, dicadmium orthophosphate hydroxide, Cd2(PO4)OH, and penta-cadmium bis-(orthophosphate) tetra-kis-(hydroxide), Cd5(PO4)2(OH)4, were obtained under hydro-thermal conditions. Cd2(PO4)OH adopts the triplite [(Mn,Fe)2(PO4)F] structure type. Its asymmetric unit comprises two Cd, one P and five O sites, all situated at the general Wyckoff position 8 f of space group I2/a; two of the O atoms are positionally disordered over two sites, and the H atom could not be localized. Disregarding the disorder, distorted [CdO6] polyhedra form a tri-periodic network by edge-sharing with neighbouring [CdO6] units and by vertex-sharing with [PO4] units. The site associated with the OH group is coordinated by four Cd atoms in a distorted tetra-hedral manner forming 1 ∞[(OH)Cd4/2] chains parallel to [001]. The oxygen environment around the OH site suggests multiple acceptor atoms for possible O-H⋯O hydrogen-bonding inter-actions and is the putative reason for the disorder. Cd5(PO4)2(OH)4 adopts the arsenoclasite [Mn5(AsO4)2(OH)4] structure type. Its asymmetric unit comprises five Cd, two P, and twelve O sites all located at the general Wyckoff position 4 a of space group P212121; the H atoms could not be localized. The crystal structure of Cd5(PO4)2(OH)4 can be subdivided into two main sub-units. One consists of three edge-sharing [CdO6] octa-hedra, and the other of two edge- and vertex-sharing [CdO6] octa-hedra. Each sub-unit forms corrugated ribbons extending parallel to [100]. The two types of ribbons are linked into the tri-periodic arrangement through vertex-sharing and through common [PO4] tetra-hedra. Qu-anti-tative structure comparisons are made with isotypic M 5(XO4)2(OH)4 crystal structures (M = Cd, Mn, Co; X = P, As, V).

Crystal structure of K6[Zn(CO3)4].

The crystal structure of K6[Zn(CO3)4], hexa-potassium tetra-carbonato-zincate(II), comprises four unique potassium cations (two located on a general position, and two on the twofold rotation axis of the space group C2/c) and a [Zn(CO3)4]6- anion. The ZnII atom of the latter is located on the twofold rotation axis and is surrounded in a slightly distorted tetra-hedral manner by two pairs of monodentately binding carbonate groups, with Zn-O distances of 1.9554 (18) and 1.9839 (18) Å. Both carbonate groups exhibit a slight deviation from planarity, with the C atom being shifted by 0.008 (2) and 0.006 (3) Å, respectively, from the plane of the three O atoms. The coordination numbers of the potassium cations range from 6 to 8, using a threshold of 3.0 Šfor K-O bonding inter-actions being significant. In the crystal structure, [KOx] polyhedra and [Zn(CO3)4]6- groups share O atoms to build up the framework structure.

A biomimetic approach for the concise total synthesis of greenwaylactams A-C.

A concise, racemic total synthesis of three sesquiterpenoid alkaloids (greenwaylactams A-C) exhibiting an unprecedented 8-membered benzolactam is disclosed. Key transformations of this work include the ring expansion through cleavage of an indole via Witkop oxidation, as well as an HFIP mediated cationic cyclisation to build up the pentacyclic carbon skeleton.

Garnet-type Na3Te2(FeO4)3.

Na3Te2(FeO4)3 or Na3Te2Fe3O12, tris-odium ditellurium(VI) triiron(III) dodeca-oxide, was obtained in the form of single-crystals under hydro-thermal conditions. Na3Te2(FeO4)3 adopts the garnet structure type in space group Ia d and comprises one Na (multiplicity 24, Wyckoff letter c, site symmetry 2.22), one Te (16 a, ..), one Fe (24 d, ..) and one O atom (96 h, 1) in the asymmetric unit. The three-dimensional framework structure is built of [TeO6] octa-hedra and [FeO4] tetra-hedra by vertex-sharing. The larger Na+ cations are situated in the inter-stices of the framework and are eightfold coordinated in the form of a distorted dodeca-hedron. Qu-anti-tative structural comparisons with isotypic Na3Te2[(Fe0.5Al0.5)O4]3 and Na3Te2(GaO4)3 show a high degree of similarity between the three crystal structures.

Crystal structures of two 1,2,3,4-tetra-hydro-naphthalenes obtained during efforts towards the total synthesis of elisabethin A.

The two substituted 1,2,3,4-tetra-hydro-naphthalenes, methyl (R)-3-{(1R,4S)-6-meth-oxy-4,7-dimethyl-5,8-bis-[(triiso-propyl-sil-yl)-oxy]-1,2,3,4-tetra-hydro-naph-th-al-en-1-yl}butano-ate, C36H66O5Si2, (2), and methyl (E)-3-{(1R,4S)-8-hy-droxy-6-meth-oxy-4,7-dimethyl-5-[(triiso-propyl-sil-yl)-oxy]-1,2,3,4-tetra-hydro-naphthalen-1-yl}acrylate, C26H42O5Si, (8), crystallize in the Sohncke space groups P212121 and P21, respectively, with the absolute structure determined on the basis of anomalous dispersion effects. The configurations of the stereo centres in the 1,2,3,4-tetra-hydro-naphthalene moiety of (2) and (8) are the same, and the conformation of the non-aromatic part of the ring system is nearly identical. In the crystal of (2), weak non-classical C-H⋯O inter-actions consolidate the packing, whereas in (8), inter-molecular O-H⋯O hydrogen-bonding inter-actions of medium-to-weak strength direct the mol-ecules into Z-shaped strands extending parallel to [010].

Dimorphism of [Bi2O2(OH)](NO3) - the ordered Pna21 structure at 100†K.

The re-investigation of [Bi2O2(OH)](NO3), dioxidodibismuth(III) hydroxide nitrate, on the basis of single-crystal X-ray diffraction data revealed an apparent structural phase transition of a crystal structure determined previously (space group Cmc21 at 173 K) to a crystal structure with lower symmetry (space group Pna21 at 100 K). The Cmc21 → Pna21 group-subgroup relationship between the two crystal structures is klassengleiche with index 2. In contrast to the crystal structure in Cmc21 with orientational disorder of the nitrate anion, disorder does not occur in the Pna21 structure. Apart from the disorder of the nitrate anion, the general structural set-up in the two crystal structures is very similar: [Bi2O2]2+ layers extend parallel to (001) and alternate with layers of (OH)- anions above and (NO3)- anions below the cationic layer. Whereas the (OH)- anion shows strong bonds to the BiIII cations, the (NO3)- anion weakly binds to the BiIII cations of the cationic layer. A rather weak O-H⋯O hydrogen-bonding inter-action between the (OH)- anion and the (NO3)- anion links adjacent sheets along [001].

Efforts toward the Total Synthesis of Elisabethin A.

We describe our efforts toward the total synthesis of the natural product elisabethin A. The first route was guided by the proposed biosynthesis, assembling the 6,6-ring system before forming the five-membered ring including the quaternary carbon. The second approach includes a high yielding cyclization under Mitsunobu conditions as a key step. It allowed the preparation of an unusual and highly functionalized bicyclic 6,5-spiro compound. Both routes share a common advanced precursor obtained from an "underdeveloped" Claisen rearrangement of an aryl dienyl ether.

Sterically Demanding Flexible Phosphoric Acids for Constructing Efficient and Multi-Purpose Asymmetric Organocatalysts.

Herein, we present a novel approach for various asymmetric transformations of cyclic enones. The combination of readily accessible chiral diamines and sterically demanding flexible phosphoric acids resulted in a simple and highly tunable catalyst framework. The careful optimization of the catalyst components led to the identification of a particularly powerful and multi-purpose organocatalyst, which was successfully applied for asymmetric epoxidations, aziridinations, aza-Michael-initiated cyclizations, as well as for a novel Robinson-like Michael-initiated ring closure/aldol cyclization. High catalytic activities and excellent stereocontrol was observed for all four reaction types, indicating the excellent versatility of our catalytic system. Furthermore, a simple change in the diamine's configuration provided easy access to both product antipodes in all cases.

The layer silicate Cs2SnIVSi6O15.

Single crystals of Cs2SnSi6O15, dicaesium tin(IV) hexa-silicate, were serendipitously obtained from a CsCl/NaCl flux at 923 K, starting from mixtures of CaO, SnO and TeO2 in a closed silica ampoule. The crystal structure of Cs2SnSi6O15 is constructed from {Si6O15}6- layers extending parallel to (101), and CsI cations with a coordination number of eleven as well as isolated [SnO6] octa-hedra situated between the silicate layers. Each of the nine different SiO4 tetra-hedra in the silicate layer has a connectedness of Q 3 (three bridging and one terminal O atom), which leads to the formation of five- and eight-membered rings. The same type of silicate layer is found in the crystal structure of the mineral zeravshanite. Comparison with other silicates of the type Cs2 M IVSi6O15 (M IV = Ti, Zr, Th, U) revealed a klassengleiche group-subgroup relationship of index 2 between Cs2ZrSi6O15 (Z = 6, space group C2/m) and Cs2SnSi6O15 (Z = 12, space group I2/c).

Polytypism in mcalpineite: a study of natural and synthetic Cu3TeO6.

Synthetic and naturally occurring forms of tricopper orthotellurate, CuII3TeVIO6 (the mineral mcalpineite) have been investigated by 3D electron diffraction (3D ED), X-ray powder diffraction (XRPD), Raman and infrared (IR) spectroscopic measurements. As a result of the diffraction analyses, CuII3TeVIO6 is shown to occur in two polytypes. The higher-symmetric CuII3TeVIO6-1C polytype is cubic, space group Ia3, with a = 9.537 (1) Šand V = 867.4 (3) Å3 as reported in previous studies. The 1C polytype is a well characterized structure consisting of alternating layers of CuIIO6 octahedra and both CuIIO6 and TeVIO6 octahedra in a patchwork arrangement. The structure of the lower-symmetric orthorhombic CuII3TeVIO6-2O polytype was determined for the first time in this study by 3D ED and verified by Rietveld refinement. The 2O polytype crystallizes in space group Pcca, with a = 9.745 (3) Å, b = 9.749 (2) Å, c = 9.771 (2) Šand V = 928.3 (4) Å3. High-precision XRPD data were also collected on CuII3TeVIO6-2O to verify the lower-symmetric structure by performing a Rietveld refinement. The resultant structure is identical to that determined by 3D ED, with unit-cell parameters a = 9.56157 (19) Å, b = 9.55853 (11) Å, c = 9.62891 (15) Šand V = 880.03 (2) Å3. The lower symmetry of the 2O polytype is a consequence of a different cation ordering arrangement, which involves the movement of every second CuIIO6 and TeVIO6 octahedral layer by (1/4, 1/4, 0), leading to an offset of TeVIO6 and CuIIO6 octahedra in every second layer giving an ABAB* stacking arrangement. Syntheses of CuII3TeVIO6 showed that low-temperature (473 K) hydrothermal conditions generally produce the 2O polytype. XRPD measurements in combination with Raman spectroscopic analysis showed that most natural mcalpineite is the orthorhombic 2O polytype. Both XRPD and Raman spectroscopy measurements may be used to differentiate between the two polytypes of CuII3TeVIO6. In Raman spectroscopy, CuII3TeVIO6-1C has a single strong band around 730 cm-1, whereas CuII3TeVIO6-2O shows a broad double maximum with bands centred around 692 and 742 cm-1.

Sterically Demanding Flexible Phosphoric Acids for Constructing Efficient and Multi-Purpose Asymmetric Organocatalysts.

Herein, we present a novel approach for various asymmetric transformations of cyclic enones. The combination of readily accessible chiral diamines and sterically demanding flexible phosphoric acids resulted in a simple and highly tunable catalyst framework. The careful optimization of the catalyst components led to the identification of a particularly powerful and multi-purpose organocatalyst, which was successfully applied for asymmetric epoxidations, aziridinations, aza-Michael-initiated cyclizations, as well as for a novel Robinson-like Michael-initiated ring closure/aldol cyclization. High catalytic activities and excellent stereocontrol was observed for all four reaction types, indicating the excellent versatility of our catalytic system. Furthermore, a simple change in the diamine's configuration provided easy access to both product antipodes in all cases.

Single crystals of SnTe3O8 in the millimetre range grown by chemical vapor transport reactions.

Tin(IV) trioxidotellurate(IV), SnTe3O8, is a member of the isotypic M IVTeIV 3O8 (M = Ti, Zr, Hf, Sn) series crystallizing with eight formula units per unit cell in space group Ia . In comparison with the previous crystal structure model of SnTe3O8 based on powder X-ray diffraction data [Meunier & Galy (1971 ▸). Acta Cryst. B27, 602-608], the current model based on single-crystal X-ray data is improved in terms of precision and accuracy. Nearly regular [SnO6] octa-hedra (Sn site symmetry ..) are situated in the voids of an oxidotellurate(IV) framework built up by corner-sharing [TeO4] bis-phenoids (Te site symmetry 2..). A qu-anti-tative structural comparison revealed a very high degree of similarity for the structures with M = Ti, Zr, Sn in the M IVTe3O8 series.

Crystal structure of Zn2(HTeO3)(AsO4).

Single crystals of Zn2(HTeO3)(AsO4), dizinc(II) hydroxidodioxidotellurate(IV) oxidoarsenate(V), were obtained as one of the by-products in a hydro-thermal reaction between Zn(NO3)2·6H2O, TeO2, H3AsO4 and NH3 in molar ratios of 2:1:2:10 at 483 K for seven days. The asymmetric unit of Zn2(HTeO3)(AsO4) contains one Te (site symmetry m), one As (m), one Zn (1), five O (three m, two 1) and one H (m) site. The ZnII atom exhibits a coordination number of 5 and is coordinated by four oxygen atoms and a hydroxide group, forming a distorted trigonal bipyramid. The hydroxide ion is positioned at a significantly larger distance on one of the axial positions of the bipyramid. The [ZnO4OH] polyhedra are connected to each other by corner-sharing to form ∞ 2[ZnO3/2(OH)1/2O1/1] layers extending parallel to (001). The TeIV atom is coordinated by three oxygen atoms and a hydroxide group in a one-sided manner in the shape of a bis-phenoid, revealing stereochemical activity of its 5s 2 electron lone pair. The AsV atom is coordinated by four oxygen atoms to form the tetra-hedral oxidoarsenate(V) anion. By corner-sharing, [TeO3OH] and [AsO4] groups link adjacent ∞ 2[ZnO3/2(OH)1/2O1/1] layers along [001] into a three-dimensional framework structure.

(NH4)Mg(HSO4)(SO4)(H2O)2 and NaSc(CrO4)2(H2O)2, two crystal structures comprising kröhnkite-type chains, and the temperature-induced phase transition (NH4)Mg(HSO4)(SO4)(H2O)2\rightleftharpoons (NH4)MgH(SO4)2(H2O)2.

The crystal structure of the mineral kröhnkite, Na2Cu(SO4)2(H2O)2, contains infinite chains composed of [CuO4(OH2)2] octahedra corner-linked with SO4 tetrahedra. Such or similar tetrahedral-octahedral `kröhnkite-type' chains are present in the crystal structures of numerous compounds with the composition AnM(XO4)2(H2O)2. The title compounds, (NH4)Mg(HSO4)(SO4)(H2O)2, ammonium magnesium hydrogen sulfate sulfate dihydrate, and NaSc(CrO4)2(H2O)2, sodium scandium bis(chromate) dihydrate, are members of the large family with such kröhnkite-type chains. At 100 K, (NH4)Mg(HSO4)(SO4)(H2O)2 has an unprecedented triclinic crystal structure and contains [MgO4(OH2)2] octahedra linked by SO3(OH) and SO4 tetrahedra into chains extending parallel to [-110]. Adjacent chains are linked by very strong hydrogen bonds between SO3(OH) and SO4 tetrahedra into layers parallel to (111). Ammonium cations and water molecules connect adjacent layers through hydrogen-bonding interactions of medium-to-weak strength into a three-dimensional network. (NH4)Mg(HSO4)(SO4)(H2O)2 shows a reversible phase transition and crystallizes at room temperature in structure type E in the classification scheme for structures with kröhnkite-type chains, with half of the unit-cell volume for the resulting triclinic cell, and with disordered H atoms of the ammonium tetrahedron and the H atom between two symmetry-related sulfate groups. IR spectroscopic room-temperature data for the latter phase are provided. Monoclinic NaSc(CrO4)2(H2O)2 adopts structure type F1 in the classification scheme for structures with kröhnkite-type chains. Here, [ScO4(OH2)2] octahedra (point group symmetry -1) are linked by CrO4 tetrahedra into chains parallel to [010]. The Na+ cations (site symmetry 2) have a [6 + 2] coordination and connect adjacent chains into a three-dimensional framework that is consolidated by medium-strong hydrogen bonds involving the water molecules. Quantitative structural comparisons are made between NaSc(CrO4)2(H2O)2 and its isotypic NaM(CrO4)2(H2O)2 (M = Al and Fe) analogues.

Redetermination of K2Mg3(OH)2(SO4)3(H2O)2 from single-crystal X-ray data revealing the correct hydrogen-atom positions.

In comparison with the previous structure determination of K2Mg3(OH)2(SO4)3(H2O)2, dipotassium trimagnesium di-hydroxide tris-(sulfate) dihydrate, from laboratory powder X-ray diffraction data [Kubel & Cabaret-Lampin (2013 ▸). Z. Anorg. Allg. Chem. 639, 1782-1786], the present redetermination against CCD single-crystal data has allowed for the modelling of all non-H atoms with anisotropic displacement parameters. As well as higher accuracy and precision in terms of bond lengths and angles, the clear localization of the H-atom positions leads also to a reasonable hydrogen-bonding scheme for this hy-droxy hydrate. The structure consists of (100) sheets composed of corner- and edge-sharing [MgO6] octa-hedra and sulfate tetra-hedra. Adjacent sheets are linked by the potassium cations and a hydrogen bond of medium strength involving the water mol-ecule. The title compound is isotypic with its CoII and MnII analogues: the three K2 M 3(OH)2(SO4)3(H2O)2 (M = Mg, Co, Mn) structures are qu-anti-tatively compared.

TlPO3 and its comparison with isotypic RbPO3 and CsPO3.

The crystal structure of thallium(I) catena-polyphosphate, TlPO3, contains a polyphosphate chain extending parallel to [010] with a repeating unit of two phosphate tetra-hedra. The TlI atom is located in-between the polyphosphate chains and is bonded by oxygen atoms in a distorted [6 + 1] coordination in the form of a monocapped prism, with the longest Tl-O bond to the bridging O atom of the polyphosphate chain. A qu-anti-tative structural comparison with isotypic RbPO3 and CsPO3 reveals that the usually pronounced stereoactivity of the 6s 2 lone pair at the TlI atom is not apparent in the case of TlPO3.