Cobalt versus Osmium: Control of Both trans and cis Selectivity in Construction of the EFG Rings of Pectenotoxin 4

Catalytic oxidative cyclisation reactions have been employed for the synthesis of the E and F rings of the complex natural product target pectenotoxin 4. The choice of metal catalyst (cobalt‐ or osmium‐based) allowed for the formation of THF rings with either trans or cis stereoselectivity. Fragment union using a modified Julia reaction then enabled the synthesis of an advanced synthetic intermediate containing the EF and G rings of the target.     

First total synthesis of (+)-crassalactone A

A simple and highly efficient first total synthesis of cytotoxic (+)-crassalactone A starting from (R)-mandelic acid is described. The strategy involves the osmium tetroxide-catalyzed cis-hydroxylation and the stereoselective addition of ethyl lithiopropiolate to a chiral aldehyde intermediate as key steps.     

A general and efficient method for the synthesis of benzo-(iso)quinoline derivatives

A new, short and efficient synthesis of substituted benzo-(iso)quinoline derivatives is reported. The methodology is based on a Suzuki or Negishi cross-coupling followed by a cyclization reaction induced by t-BuOK in DMF to form the central ring. This approach allowed the synthesis of all four benzo-(iso)quinoline isomers and the substitution of each ring of the benzo-(iso)quinoline core.     

Concise Total Synthesis of (−)-Vermiculine through a Rhodium-Catalyzed C2-Symmetric Dimerization Strategy

A short and efficient synthesis of the C₂-symmetric antibiotic (−)-vermiculine by utilizing an enantioselective catalytic one-step dimerization methodology as key-step to construct the core structure is reported. The late-stage modifications feature a double metathesis homologation followed by a double Wacker-type oxidation. These key-steps allowed the synthesis of vermiculine in only seven steps, starting from commercially available building blocks.     

Chemoenzymatic total synthesis of potent HIV RNase H inhibitor (−)-1,3,4,5-tetragalloylapiitol

Starting from racemic dimethyl 2-acetoxy-3-methylenesuccinate, the chemoenzymatic facile total synthesis of (−)-1,3,4,5-tetragalloylapiitol has been demonstrated via an efficient lipase catalyzed resolution followed by a DIBAL reduction-double gallyolation, osmium tetroxide dihydroxylation-double gallyolation, and reductive global O-benzyl deprotection pathway.     

Osmium Polypyridyl Complexes and Their Applications to Dye‐Sensitized Solar Cells

Dye‐sensitized solar cells (DSSCs) have received much attention in recent years owing to their efficient conversion of sunlight to electricity. DSSCs became successful alternatives to silicon photovoltaic devices by virtue of their low fabrication costs and easy preparation methods. In DSSCs the dye plays the key role. This review summarizes the applications of osmium sensitizers in DSSCs. We also briefly discussed their synthesis and the effect of various electrolyte systems on device efficiencies.     

A trifunctional catalyst for one-pot synthesis of chiral diols via Heck coupling-N-oxidation-asymmetric dihydroxylation: application for the synthesis of diltiazem and taxol side chain

A heterogeneous bifunctional catalyst composed of OsO4(2-)-WO4(2-) and a trifunctional catalyst comprising PdCl4(2-)-OsO4(2-)-WO4(2-), designed and prepared by an ion-exchange technique using layered double hydroxides (LDH) as an ion-exchanger and their homogeneous bifunctional analogue, K2OsO4-Na2WO4 and trifunctional analogue, Na2PdCl4-K2OsO4-Na2WO4, devised for the first time are evaluated for the synthesis of chiral vicinal diols. These bifunctional and trifunctional catalysts perform asymmetric dihydroxylation-N-oxidation and Heck-asymmetric dihydroxylation-N-oxidation, respectively, in the presence of Sharpless chiral ligand, (DHQD)2PHAL in a single pot using H2O2 as a terminal oxidant to provide N-methylmorpholine oxide (NMO) in situ by the oxidation of N-methylmorpholine (NMM). The heterogeneous bifunctional catalyst supported on LDH (LDH-OsW) displays superior activity to afford diols with higher yields over the other heterogeneous catalysts developed by the ion exchange on quaternary ammonium salts covalently bound to resin (resin-OsW) and silica (silica-OsW) or homogeneous catalysts in the achiral dihydroxylation reactions. The LDH-OsW and its homogeneous analogue are found to be very efficient in performing a simultaneous asymmetric dihydroxylation (AD)-N-oxidation of a wide and varied range of aromatic, cyclic, and mono, di-, and trisubstituted olefins to obtain chiral vicinal diols with higher yields and ee's using H2O2. Further, the use of OsO4(2-)-WO4(2-) catalysts as such or in the supported form offers a simplified procedure for catalyst recycling, which shows consistent activity for a number of cycles. In this process, Os(VI) is recycled to Os(VIII) by a coupled electron transfer-mediator (ETM) system based on NMO-WO4(2-) using H2O2, leading to a mild and selective electron transfer. The one-pot biomimic synthesis of chiral diols is mediated by a recyclable trifunctional heterogeneous catalyst (LDH-PdOsW) consisting of active palladium, tungsten, and osmium species embedded in a single matrix. This protocol, which provides prochiral olefins and NMO in situ by Heck coupling and N-oxidation of NMM, respectively, required for the AD, unfolds a low cost process. We extended the present method to the one-pot synthesis of trisubstituted chiral vicinal diols with moderate to excellent ee's by AD of trisubstituted olefins that are obtained by in situ Heck arylation of disubstituted olefins. The heterogeneous trifunctional catalysts offers chiral diols with unprecedented ee's and excellent yields in the AD of prochiral cinnamates, which are obtained in situ from acrylates and halobenzenes for the first time. The new variants such as LDH support and Et3N*HX inherently composed in the heterogeneous multicomponent system and slow addition of H2O2 facilitates the hydrolysis of osmium monogylcolate ester to subdue the formation of bisglycolate ester to achieve higher ee's. Without resorting to recrystallization, the chiral diols of cinnamates thus synthesized with 99% ee's and devoid of osmium contamination are directly put to use in the synthesis of diltiazem and Taxol side chain with an overall improved yield to demonstrate the synthetic utility of the trifunctional heterogeneous catalyst. The high binding ability of the heterogeneous osmium catalyst enables the use of equimolar ratio of ligand to osmium to give excellent ee's in AD in contrast to the homogeneous osmium system in which the excess molar quantities of the expensive chiral ligand to osmium are invariably used. Further, the XRD, FT-IR, UV-vis DRS, and XPS studies indicate the retention of the coordination geometries of the specific divalent anions anchored to LDH matrix in their monomeric form during the ion exchange and after the reaction.     

Synthesis and arylation of unprotected sulfonimidamides

Herein we evaluate different methodologies for the synthesis of unprotected sulfonimidamides. Three different procedures that allow orthogonal deprotection of the imine nitrogen under acidic, nucleophilic, and basic conditions were established. Moreover, we present a highly efficient methodology for functionalization of the imine nitrogen through Pd-catalyzed C–N arylation. RuPhos ligand was shown to allow short reaction time, excellent yields, and allowed coupling of both aryl halides and heteroaryl bromides.     

Toward the Control of the Creation of Mixed Monolayers on Glassy Carbon Surfaces by Amine Oxidation

A versatile and simple methodology for the creation of mixed monolayers on glassy carbon (GC) surfaces was developed, using an osmium–bipyridyl complex and anthraquinone as model redox probes. The work consisted in the electrochemical grafting on GC of a mixture of mono‐protected diamine linkers in varying ratios which, after attachment to the surface, allowed orthogonal deprotection. After optimisation of the deprotection conditions, it was possible to remove one of the protecting groups selectively, couple a suitable osmium complex and cap the residual free amines. The removal of the second protecting group allowed the coupling of anthraquinone. The characterisation of the resulting surfaces by cyclic voltammetry showed the variation of the surface coverage of the two redox centres in relation to the initial ratio of the linking amine in solution.     

One-Pot Synthesis of Dihalo(porphyrinato)osmium(IV) Complexes. Evidence for Monohalo(carbonyl)osmium(III) Intermediates

trans-Dichloro-, trans-dibromo-, and trans-diiodoosmium(IV) tetraarylporphyrins were obtained by extremely facile synthetic routes directly from the reactions of the corresponding (carbonyl)osmium(II) complexes with CCl(4), CBr(4), and CI(4), respectively. At short reaction times, appreciable amounts of intermediates-one for each reaction-were observed by spectroscopic investigations. These intermediates were shown to be (carbonyl)(halo)(porphyrinato)osmium(III) complexes by independent preparation of an authentic (carbonyl)(bromo)(porphyrinato)osmium(III) complex, which was identical to the reaction intermediate in the reaction of CBr(4) and very similar to those of the other reactions. This provided strong evidence for the reaction mechanism, two stepwise one-electron oxidations of the metal ion. The relatively strong binding of carbon monoxide to osmium(III) is proposed to be an important factor in avoiding dimerization of the reaction intermediates.     

Enantioselective synthesis of saframycin A and evaluation of antitumor activity relative to ecteinascidin/saframycin hybrids

[formula: see text] A short synthesis of saframycin A is described which begins with a readily available intermediate previously utilized for the total synthesis of ecteinascidin 743. A key step in this synthesis is the use of 1-fluoro-3,5-dichloropyridinium triflate to oxidize a phenolic ring to a 1,4-benzoquinone unit while simultaneously cleaving a methoxymethyl ether of a different phenolic ring to the corresponding phenol (4-->5). The common intermediate (2) for the synthesis of saframycin A (1) and ecteinascidin 743 also allowed the synthesis of two hybrids of these structures (6 and 7). Whole cell bioassays for antitumor activity using lung, colon, melanoma, and prostate-derived tumor cell lines allowed a clear correlation of structure with biological activity in this series.     

Generation and reactions of oxiranyllithiums by use of a flow microreactor system

A flow microreactor system consisting of micromixers and microtubes provides an effective reactor for the generation and reactions of aryloxiranyllithiums without decomposition by virtue of short residence time and efficient temperature control. The deprotonation of styrene oxides with sBuLi can be conducted by using the flow microreactor system at -78 or -68 °C (whereas much lower temperatures (< -100 °C) are needed for the same reactions conducted under macrobatch conditions). The resulting α-aryloxiranyllithiums were allowed to react with electrophiles in the flow microreactor system at the same temperature. The sequential introduction of various electrophiles onto 2,3-diphenyloxiranes was also achieved by using an integrated flow microreactor, which serves as a powerful system for the stereoselective synthesis of tetrasubstituted epoxides.     

Recent advances in the synthesis,structural diversity,and applications of mesoionic 1,2,3-triazol-5-ylidene metal complexes

Beyond the classic N-heterocyclic carbenes (NHCs) there is a subclass of NHCs called mesoionic carbenes (MICs). This review focuses on recent advances in the area of 1,2,3-triazol-5-ylidenes as the most abundant class of MICs and their metal complexes. The study of mesoionic 1,2,4- and 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene transition metal complexes is a research area with a history of just ～10 years. During this relatively short period, hundreds of these complexes have appeared in the literature, reflecting their high stability and simpler synthesis compared with NHCs. Specifically, this review is focused on advances in the synthesis of 1,2,3-triazol-5-ylidene metal complexes derived from palladium, silver, gold, ruthenium, iridium, rhodium, iron, molybdenum, cobalt, nickel, platinum, and osmium, together with their catalytic, medicinal, and photophysical applications.     

Synthesis and structural characterization of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand

Treatment of dibromo(pentamethylcyclopentadienyl)osmium(III) dimer with alkali metal salts of a variety of cyclopentadienyl derivatives provides a simple approach to the synthesis of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand. Furthermore, the reaction of dibromo(pentamethylcyclopentadienyl)osmium(III) with alkali metal salts of pyrrole and 3,5-di-tert-butylpyrazole afforded the corresponding pentamethylcyclopentadienylosmium complexes containing η⁵-pyrrolyl or η⁵-3,5-di-tert-butylpyrazolato ligands. This overall synthetic approach afforded pentamethylosmocene (64%), (η⁵-pentamethylcyclopentadienyl)(η⁵-indenyl)osmium (36%), (η⁵-pentamethylcyclopentadienyl)(η⁵-fluorenyl)osmium (30%), (η⁵-pyrrolyl)(η⁵-pentamethylyclopentadienyl)osmium (30%), and (η⁵-3,5-di-tert-butylpyrazolato)(η⁵-pentamethylcyclopentadienyl)osmium (38%). The new complexes were characterized by spectroscopic and analytical techniques, and by single crystal X-ray structural determinations. In the solid state, all of the new complexes exist as eclipsed metallocenes.     

Chemically-enabled synthesis of 1,2,3,4-tetrahydroisoquinolin-1-ones

We have developed a number of efficient protocols for the facile synthesis of 1,2,3,4-tetrahydroisoquinolin-1-ones. This synthetic methodology allowed concise and efficient exploration of the SAR in all areas of the molecule. A number of these methods proved to be versatile, efficient and amenable to parallel synthesis.     

Pentacyclic and Hexacyclic Osmaarynes and Their Derivatives

Although osmabenzyne, osmanaphthalyne, osmaphenanthryne, and osmaanthracyne have been previously reported, the synthesis of polycyclic osmaarynes is still a challenge. Herein, we report the successful synthesis of the first pentacyclic osmaarynes (pyreno[b]osmabenzynes 1 a and 2 a ) and hexacyclic osmaaryne (peryleno[b]osmabenzyne 3 a ). Nucleophilic reaction of osmaarynes was used to obtain the corresponding pyreno[b]osmium complexes ( 1 and 2 ) and peryleno[b] osmium complex ( 3 ), which exhibited near-infrared luminescence and aggregation-induced emission (AIE) properties. Complexes 2 and 3 are resistant to photodegradation, and complex 2 has better photothermal conversion properties than 3 .     

Enantioselective Synthesis of Phenylpropanetriols

The four stereomer 1-(4-hydroxy-3-methoxy)-phenyl-1,2,3-propanetriols were obtained in about 30% yields starting from ferulic acid by a synthesis based on osmium catalyzed asymmetric dihydroxylation.     

Syntheses and structures of Osmium(II) and Osmium(VI) <Emphasis Type="Italic">meso</Emphasis>-tetra(benzo-15-crown-5)porphyrinates according to the spectral data

The reaction of meso-tetra(benzo-15-crown-5)porphyrin (H₂TCP) with the osmium carbonyl complex Os₃(CO)₁₂ yieds the corresponding osmium(II) porphyrinate OsTCP(CO). The oxidation of OsTCP(CO) with air oxygen and hydrogen peroxide in neutral and acidic media was studied. A preparative method for the synthesis of osmium(VI) meso-tetra(benzo-15-crown-5)porphyrinate (OsO₂) TCP by the oxidation of OsTCP(CO) with 50% hydrogen peroxide in acetic acid was developed. The structures of new osmium porphyrinates were determined by IR, ¹H NMR, and UV/Vis spectroscopies.     

Combining two-directional synthesis and tandem reactions: a short formal synthesis of halichlorine

A short and efficient synthesis of an advanced intermediate (1) in the Clive route to halichlorine has been achieved in 12 steps and 13.2% yield by a combined two-directional synthesis/tandem reaction strategy.     

The novel and efficient direct synthesis of N,O-acetal compounds using a hypervalent iodine(III) reagent: an improved synthetic method for a key intermediate of discorhabdins

The use of hypervalent iodine(III) reagents allowed us to develop the novel and efficient direct synthesis of N,O-acetal compounds via the oxidative fragmentation reaction of alpha-amino acids or alpha-amino alcohols; furthermore, we succeeded in developing an improved synthesis of the key intermediate of discorhabdins.