C1 and C2-symmetric carbohydrate phosphorus ligands in asymmetric catalysis

Layer by Layer Spraying Fabrication of Aggregation-Induced Emission Metal-Organic Frameworks Thin Film

The development of new metal-organic frameworks (MOFs) thin films is important for expanding their functions and applications. Herein, we first report a new kind of MOF thin film by using aggregation-induced emission (AIE) dicarboxyl ligand through a liquid-phase epitaxial (LPE) layer-by-layer (LBL) spraying method (named AIE surface-coordinated metal-organic frameworks thin film, AIE-SURMOF). The obtained AIE-SURMOF Zn4O(TPE)3 (ZnTPE) has highly growth orientation and homogeneous thin film, showing strong fluorescent property. Furthermore, by loading chiral guest in the MOF pore, the formed chiral encapsulated AIE-SURMOF can clearly indicate obvious circularly polarized luminescence performance with glum of 0.01. This study provides new MOF thin film and new strategy for expanding function and application of MOF materials.

A recyclable stereoauxiliary aminocatalyzed strategy for one-pot synthesis of indolizine-2-carbaldehydes

Indolizine-carbaldehydes with the easily modifiable carbaldehyde group are important synthetic targets as versatile precursors for distinct indolizines. However, the efficient one-pot construction of trisubstituted indolizine-2-carbaldehydes represents a long-standing challenge. Herein, we report an unprecedented recyclable stereoauxiliary aminocatalytic approach via aminosugars derived from biomass, which enable the efficient one-pot synthesis of desired trisubstituted indolizine-2-carbaldehydes via [3+2] annulations of acyl pyridines and α,β-unsaturated aldehyde. Compared to the steric shielding effect from α-anomer, a stereoauxiliary effect favored by β-anomer of D-glucosamine is supported by control experiments. Furthermore, polymeric chitosan containing predominantly β-D-anhydroglucosamine units also shows excellent catalytic performance in aqueous solutions for the conversion of various substrates, large-scale synthesis and catalytic cycling experiments. Thus, our approach advances the existing methodologies by providing a rich library of indolizine-2-aldehydes. In addition, it delivers an efficient protocol for a set of late-stage diversification and targeted modifications of bioactive molecules or drugs, as showcased with 1,2,3-trisubstituted indolizine-2-carbaldehydes.

Carbohydrate‐functionalized triazolylidene iridium complexes: hydrogenation catalysis in water with asymmetric induction

Two sets of carbohydrate‐NHC hybrid iridium complexes were synthesised in order to combine properties of carbohydrates and triazolylidene (trz) ligands in organometallic catalysis. One set features a direct trz linkage to the anomeric carbohydrate carbon, while the second set is comprised of an ethyl linker between the two functional units. Deprotection of the carbohydrate afforded hybrid complexes that efficiently catalyse the direct hydrogenation of ketones in water. The catalytic activity of the hybrid complexes was influenced by the pH of the aqueous medium and surpassed the activity of carbohydrate‐free or acetyl‐protected analogues (>90 % vs 13 % yield). While no enantiomeric induction was observed for the ethyl‐linked hybrids, a moderate enantiomeric excess (ee) was induced by the directly linked systems. Moreover, these carbohydrate‐trz hybrid complexes displayed mixed inhibitory activity towards a glycosidase from H. orenii that contain a glucose binding site.

Bismuth species in the coordination sphere of transition metals: synthesis, bonding, coordination chemistry, and reactivity of molecular complexes

This contribution is focused on bismuth species in the coordination sphere of transition metals. In molecular transition metal complexes, three types of Bi-M bonding are considered, namely dative Bi→M interactions (with Bi acting as a donor), dative Bi←M interactions (with Bi acting as an acceptor) and covalent Bi-M interactions (M = transition metal). Synthetic routes to all three classes of compounds are outlined, the Bi-M bonding situation is discussed, trends in the geometric parameters and in the coordination chemistry of the compounds are addressed, and common spectroscopic properties are summarized. As an important part of this contribution, the reactivity of bismuth species in the coordination sphere of transition metal complexes in stoichiometric and catalytic reactions is highlighted.

Carbohydrate-functionalized N-heterocyclic carbene Ru(ii) complexes: synthesis, characterization and catalytic transfer hydrogenation activity

Triazolylidene NHCs decorated with a carbohydrate wingtip group were complexed to a ruthenium(ii) center. Deprotection of the carbohydrate in the metal complex affords a carbohydrate–NHC hybrid system for use as a transfer hydrogenation catalyst.

Silver-promoted cascade radical cyclization of γ,δ-unsaturated oxime esters with P(O)H compounds: synthesis of phosphorylated pyrrolines

We report the first silver-promoted imino-phosphorylation of γ,δ-unsaturated oxime esters with P(O)H compounds to synthesize various phosphorylated pyrrolines.

D-Fructose-based spiro-fused PHOX ligands: synthesis and application in enantioselective allylic alkylation

Phosphinooxazoline (PHOX) ligands are an important class of ligands in asymmetric catalysis. We synthesized ten novel D-fructose-derived spiro-fused PHOX ligands with different steric and electronic demand. The application of two of them was tested in asymmetric allylic alkylation. The ligands are prepared in two steps from readily available 1,2-O-isopropylidene protected β-D-fructopyranoses by the BF₃·OEt₂-promoted Ritter reaction with 2-bromobenzonitrile to construct the oxazoline moiety followed by Ullmann coupling of the resulting aryl bromides with diphenylphosphine. Both steps proceeded mostly in good to high yields (57–86% for the Ritter reaction and 35–89% for the Ullmann coupling). The Ritter reaction gave two anomers, which could be separated by column chromatography. The prepared ligands showed promising results (er of up to 84:16) in Tsuji–Trost reactions with diphenylallyl acetate as model substrate.

Decarboxylative cross-coupling reactions for P(O)-C bond formation

Phosphorus-containing compounds are one of the most important classes of organic compounds, which have wide applications in organic chemistry, medicinal chemistry, agricultural chemistry, and materials chemistry. In particular, organophosphorus compounds bearing a P(O)-C bond have attracted significant attention in recent decades due to their widespread biological and pharmacological activities. In this review, we will highlight the most important developments in the construction of P(O)-C bonds through decarboxylative C-P cross-coupling reactions. The literature has been surveyed from 2011 to May 2018.

Sugar-Annulated Oxazoline Ligands: A Novel Pd(II) Complex and Its Application in Allylic Substitution

Two novel carbohydrate-derived pyridyl (PYOX)- and cyclopropyl (CYBOX)-substituted oxazoline ligands were prepared from d-glucosamine hydrochloride and 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-β-d-glucopyranose hydrochloride in two steps, respectively. The sugar-annulated PYOX ligand formed a stable metal complex with Pd(II), which was fully characterized by NMR spectroscopy and X-ray crystallography. NMR and X-ray analysis revealed a change of the conformation in the sugar moiety upon complexation with the palladium(II) species. Both glycosylated ligands resulted in high asymmetric induction (up to 98% ee) upon application as chiral ligands in the Pd-catalyzed allylic alkylation of rac-1,3-diphenylallyl acetate with dimethyl malonate (Tsuji-Trost reaction). Both ligands provided mainly the (R)-enantiomer of the alkylation product.

Spiro-fused carbohydrate oxazoline ligands: Synthesis and application as enantio-discrimination agents in asymmetric allylic alkylation

In the present work, we describe a convenient synthesis of spiro-fused D-fructo- and D-psico-configurated oxazoline ligands and their application in asymmetric catalysis. The ligands were synthesized from readily available 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-fructopyranose and 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-psicopyranose, respectively. The latter compounds were partially deprotected under acidic conditions followed by condensation with thiocyanic acid to give an anomeric mixture of the corresponding 1,3-oxazolidine-2-thiones. The anomeric 1,3-oxazolidine-2-thiones were separated after successive benzylation, fully characterized and subjected to palladium catalyzed Suzuki–Miyaura coupling with 2-pyridineboronic acid N-phenyldiethanolamine ester to give the corresponding 2-pyridyl spiro-oxazoline (PyOx) ligands. The spiro-oxazoline ligands showed high asymmetric induction (up to 93% ee) when applied as chiral ligands in palladium-catalyzed allylic alkylation of 1,3-diphenylallyl acetate with dimethyl malonate. The D-fructo-PyOx ligand provided mainly the (R)-enantiomer while the D-psico-configurated ligand gave the (S)-enantiomer with a lower enantiomeric excess.

Pseudo enantiomeric mixed S/P ligands derived from carbohydrates for the 1,4-addition of phenyl boronic acid to cyclohexenone

Mixed S/P ligands 3 and 10, good catalyst precursors for the Rh(i)-catalysed 1,4-addition of phenylboronic acid to cyclohexenone behave as enantiomers even though both derived from d-sugars.

Synthesis of spirofused carbohydrate-oxazoline based palladium(II) complexes

Four carbohydrate-derived 2-pyridyl and 2-quinolinyl substituted spiro-oxazoline ligands were prepared from 3,4,5-tri-O-benzyl-1,2-di-O-isopropylidene-β-D-fructose in four steps. Conversion of the latter compound with trimethylsilylazide followed by hydrogenation gave an anomeric mixture of 2-amino-3,4,5-tri-O-benzyl-2-deoxy-1-O-trimethylsilyl-D-fructopyranose. Amide coupling of the fructosylamines with picolinic acid and quinaldic acid, respectively afforded the corresponding anomeric amidofructosides, which were both separated and characterized by NMR spectroscopy and X-ray crystallography. Cyclization of alpha-amides was achieved by treatment of the corresponding mesylates with NaH while beta-amides were directly cyclisized with NCS and Ph3P to give the corresponding 2-pyridyl (PyOx) and 2-quinolyl (QuinOx) substituted spiro-oxazoline ligands, respectively. The 2-pyridyl substituted spiro-oxazoline ligands PyOx formed stable complexes with Pd(II), which were fully characterized and their structure determined by X-ray crystallography, whereas the corresponding QuinOx ligands failed to form similar Pd complexes.

Glyconanosynthons as powerful scaffolds and building blocks for the rapid construction of multifaceted, dense and chiral dendrimers

The arsenal of available carbohydrates can be manipulated to provide versatile building blocks toward the syntheses of complex and chiral dendrimers.

Ruthenium and osmium complexes of hemilabile chiral monophosphinite ligands derived from 1D-pinitol or 1D-chiro-inositol as catalysts for asymmetric hydrogenation reactions

The monophosphinite ligands, 1D-1,2;5,6-di-O-cyclopentylidene-3-O-methyl-4-O-diphenylphosphino-chiro-inositol (D-P1), 1D-1,2;5,6-di-O-isopropylidene-3-O-methyl-4-O-diphenylphosphino-chiro-inositol (D-P2), 1D-1,2;5,6-di-O-cyclohexylidene-3-O-methyl-4-O-diphenylphosphino-chiro-inositol (D-P3), and 1D-1,2;5,6-di-O-cyclopentylidene-3-O-ethyl-4-O-diphenylphosphino-chiro-inositol (D-P4), can be conveniently prepared from the chiral natural products 1D-pinitol or 1D-chiro-inositol. On treatment of toluene solutions of RuCl2(PPh3)3 with two mole equivalents of the ligands D-PY (Y = 1-4) the complexes RuCl2(D-P1)2 (1), RuCl2(D-P2)2 (4), RuCl2(D-P3)2 (5), or RuCl2(D-P4)2 (6), respectively, are formed. Similarly, treatment of OsCl2(PPh3)3 with D-P1 gives OsCl2(D-P1)2 (7). The single crystal X-ray structure determination of 1 reveals that each D-P1 ligand coordinates to ruthenium through phosphorus and the oxygen atom of the methoxyl group. Treatment of 1 with excess LiBr or LiI results in metathesis of the chloride ligands and RuBr2(D-P1)2 (2) or RuI2(D-P1)2 (3), respectively, are formed. Exposure of a solution of 1 to carbon monoxide results in the very rapid formation of RuCl2(CO)2(D-P1)2 (8), thereby demonstrating the ease with which the oxygen donors are displaced from the metal and hence the hemilabile nature of the two bidentate D-P1 ligands in 1. Preliminary studies indicate that 1-7 act as catalysts for the asymmetric hydrogenation reactions of acetophenone and 3-quinuclidinone to give the corresponding alcohols in generally high conversions but low enantiomeric excesses.

Carbohydrate-based N-heterocyclic carbenes for enantioselective catalysis

Versatile syntheses of C2-linked and C₂-symmetric carbohydrate-based NHC·HCls from functionalised amino-carbohydrate derivatives are reported. The corresponding Rh complexes were evaluated in asymmetric hydrosilylation of ketones.

Stereospecific synthesis and catalytic activity of L-histidylidene metal complexes

We report on the synthesis, metal coordination, and catalytic impact of histidylidene, a histidine-derived N-heterocyclic carbene (NHC) ligand. The histidinium salt 3, comprising methyl substituents at both heterocyclic nitrogens and protected at the C- and N-terminus of the amino acid, was rhodated and iridated by a transmetallation protocol using Ag(2)O. Ambient temperature and short reaction times were pivotal for full retention of configuration at the α-carbon. The stereospecificity of the reaction was conveniently probed by (31)P NMR spectroscopy after transmetallation with rhodium(I) and coordination of enantiopure (S)-Ph-binepine. The histidylidene rhodium complexes are highly efficient catalysts for the mild hydrosilylation of ketones. For the cationic complexes [Rh(cod)(histidylidene)(phosphine)](+), lowering the temperature shifted the rate-limiting step of the catalytic reaction to an earlier stage that is not enantioselective. Hence the asymmetric induction-which is governed by the chiral phosphine-did not improve at low temperature.