Asymmetric synthesis of α-substituted alkylphosphonates based on symmetrical dialkyl phosphites

Chiral C₂-symmetrical dialkyl phosphites and C₃-symmetrical trialkyl phosphites, derived from (−)-borneol, (−)-menthol, and 1,2∶5,6-di-O-isopropylidene-α-d-glucofuranose, were studied as the starting reagents for the preparation of chiral organophosphorus compounds. The reactions of C₂-symmetrical dialkyl phosphites and C₃-symmetrical trialkyl phosphites with aldehydes and amines or aldehydes are accompanied by asymmetrical induction at the α-carbon atom to yield optically active α-aminoalkylphosphanates or α-hydroxyalkylphosphonates, respectively. The stereoselectivity of the reaction depends on the structure of the starting compounds and the reaction conditions. Translated fromIzvestiya Akademii, Nauk, Seriya Khimicheskaya, No. 8, pp. 1588–1593, August, 1999.     

Optical fibre beam delivery of high-energy laser pulses: beam quality preservation and fibre end-preparation

This paper investigates the extension of optical fibre beam delivery to high-brightness applications, in particular laser percussion drilling, where both a good beam quality and high peak power are required. Beam quality preservation through a number of optical fibres is studied both experimentally and by using a ray propagation model. It is determined that in order to achieve the beam quality required for percussion drilling (M²<30) the largest fibre which can be used is 400 μm diameter. The laser-induced damage threshold is measured for a number of 400 μm fibres, and a CO₂ laser-annealing technique is shown to increase the damage threshold by a factor of 10, allowing 28 J, 1 ms pulses to be transmitted.     

Grenzen für die Bildung lamellarer Metall‐di(arensulfonyl)amide: Drei Lithium‐Komplexe und ein Cadmium‐Komplex

Structures of Ionic Di(arenesulfonyl)amides. 6. Limits to the Formation of Lamellar Metal Di(arenesulfonyl)amides: Three Lithium Complexes and One Cadmium Complex According to low‐temperature X‐ray studies, the new compounds LiN(SO₂C₆H₄‐4‐X)₂ · 2 H₂O, where X = COOH ( 1 ) or COOMe ( 2 ), LiN(SO₂C₆H₄‐4‐CONH₂)₂ · 4 H₂O ( 3 ), and Cd[N(SO₂C₆H₄‐4‐COOH)₂]₂ · 8 H₂O ( 4 ) crystallize in the triclinic space group P1 ( 1 – 3 : Z′ = 1; 4 : Z′ = 1/2, Cd²⁺ on an inversion centre) and display almost perfectly folded anions approximating to mirror symmetry. The lithium ions in 1 – 3 have distorted tetrahedral environments respectively set up by two O=S groups drawn from different anions and two water molecules, two O=S groups of a chelating anion and two water molecules, or one O=C group and three water ligands, whereas the cation of 4 is fully hydrated to form an octahedral [Cd(H₂O)₆]²⁺ complex. The structure refinements for 3 and 4 were marred by positional disorder of the non‐coordinating N(SO₂)₂ moieties. Compounds 1 and 4 extend a previously described series of lamellar metal di(arenesulfonyl)amides where the two‐dimensional inorganic component is comprised of cations, N(SO₂)₂ groups and water molecules and the outer regions are formed by the 4‐substituted phenyl rings. Both crystal packings are governed by self‐assembly of parallel layers through exhaustive hydrogen bonding between carboxylic groups, and there is good evidence that the labile inorganic networks, generated via Li–O and hydrogen bonds in 1 or solely hydrogen bonds in 4 , are efficiently stabilized by the strong cyclic (COOH)₂ motifs within the interlayer regions. In the absence of these, the lamellar architecture is seen to collapse in 2 and 3 , where the carboxyl groups are replaced by methoxycarbonyl or carbamoyl functions and the inorganic components are segregated in parallel tunnels pervading the anion lattices.     

Zweidimensionale Polymere mit hydrophober Umhüllung: Kristallstrukturen der isostrukturellen Metallkomplexe [M{C6H4(SO2)2N}(H2O)] (M = K,Rb) und des strukturverwandten Ammoniumsalzes [(NH4){C6H4(SO2)2N}(H2O)]

Metal Salts of Benzene‐1,2‐di(sulfonyl)amine. 4. Hydrophobically Wrapped Two‐Dimensional Polymers: Crystal Structures of the Isostructural Metal Complexes [M{C₆H₄(SO₂)₂N}(H₂O)] (M = K, Rb) and of the Structurally Related Ammonium Salt [(NH₄){C₆H₄(SO₂)₂N}(H₂O)] The previously unreported compounds KZ · H₂O ( 1 ), RbZ · H₂O ( 2 ) and NH₄Z · H₂O ( 3 ), where Z^– is Ndeprotonated ortho‐benzenedisulfonimide, are examples of layered inorgano‐organic solids, in which the inorganic component is comprised of metal or ammonium cations, N(SO₂)₂ groups and water molecules and the outer regions are formed by the planar benzo rings of the anions. The metal complexes 1 and 2 were found to be strictly isostructural, whereas 3 is structurally related to them by a non‐crystallographic mirror plane ( 1 – 3 : monoclinic, space group P2₁/c, Z = 4; single crystal X‐ray diffraction at low temperatures). In each structure, the five‐membered 1,3,2‐dithiazolide heterocycle possesses an envelope conformation, the N atom lying about 40 pm outside the mean plane of the S–C–C–S moiety. The metal complexes feature two‐dimensional coordination networks interwoven with O–H…O hydrogen bonds originating from the water molecules. The metal centres adopt an irregular nonacoordination formed by five sulfonyl O atoms, two N atoms and two μ₂‐bridging water molecules; each M⁺ is connected to four different anions. When NH₄⁺ is substituted for M⁺, the metal–ligand bonds are replaced by N⁺–H…O hydrogen bonds, but the general topology of the lamella is not affected. In the three structures, the lipophilic benzo groups protrude obliquely from the surfaces of the polar lamellae and display marked interlocking between adjacent layers.     

A Comparison of In‐Vitro and In‐Vivo Degradation of Poly(D,L‐lactide) Bio‐Absorbable Intra‐Medullary Plugs

Poly(D ,L ‐lactide) has been evaluated as a material for the manufacture of intra‐medullary plugs to be used in total hip arthoplasty. Plugs were manufactured by compression moulding and subjected to in‐vitro and in‐vivo degradation. In‐vitro hydrolysis was carried out by immersion in phosphate buffered saline (Ringer's solution) at 37°C and rates of degradation were relatively rapid with molecular weight halving after 30 days. In‐vivo degradation was assessed by implantation into dogs followed by retrieval at intervals up to 24 months. Molecular weight was found to reduce to half the original value in about 190 days. It is thought that this difference in degradation rate is because of diffusional control of the overall process. Histology showed that the implanted plugs were resorbed over 24 months.     

Vier Natrium‐di(arensulfonyl)amide: Lamellare Schichten mit kurzen Zwischenschichtkontakten C–H…O(Nitro), C–H…F–C oder C–I…I–C

Structures of Ionic Di(arenesulfonyl)amides. 3. Four Sodium Di(arenesulfonyl)amides: Lamellar Layers Exhibiting Short C–H…O(nitro), C–H…F–C, or C–I…I–C Interlayer Contacts Low‐temperature X‐ray crystal structures are reported for NaN(SO₂C₆H₄‐4‐X)₂ · n H₂O, where X = NO₂ and n = 3 ( 1 , monoclinic, space group P2₁, Z = 2), X = F and n = 3 ( 2 , monoclinic, P2₁/c, Z = 4), X = F and n = 1 ( 3 , orthorhombic, Pccn, Z = 8), or X = I and n = 1 ( 4 , monoclinic, P2₁/c, Z = 4). The four compounds are examples of layered inorgano‐organic solids where the inorganic component is comprised of metal cations, N(SO₂)₂ groups and H₂O molecules and the outer regions are formed by the 4‐substituted phenyl rings of the folded anions. In the two‐dimensional coordination networks, the cations adopt either an octahedral [Na(O–S)₂(OH₂)₄] ( 1 , 2 ) or a distorted monocapped octahedral [NaN(O–S)₄(OH₂)₂] ( 3 , 4 ) environment. Taking into account the differing crystal symmetries within the two pairs of compounds, it is remarkable that the trihydrates 1 / 2 and the monohydrates 3 / 4 each display chemically identical and nearly isometric Na–O or Na–O/N networks. In the crystal packings, parallel layers are connected through weak hydrogen bonds C–H…O(nitro) ( 1 ) or C–H…F ( 2 , 3 ), or through short “type I” I…I contacts ( 4 ). There is good evidence that the strikingly distinct crystal symmetries in the halogenated homologues 3 / 4 are determined by the specific complementarity requirements of the interlayer binding centres.