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Double polymeric grafted layer is constructed by two steps of chemical reaction, in which two polymers had been used, respectively polydopamine (PDA) film and modified PASS (NH

A monodisperse CeO2@N-C ultrathin nanosheet self-assembled hierarchical structure (USHR) has been prepared by metal-organic framework template methods. The uniform coating of nitrogen-doped carbon (N-C) layers could play an important role in the adsorption and activation of benzylic alcohol. The unique 3D hierarchical structure self-assembled by ultrathin nanosheets provided enough active sites for the catalytic reaction. Therefore, the CeO2@N-C USHR can afford excellent catalytic performance for selective oxidation of benzylic alcohols in water.

The development of multikilogram scale green and economical synthetic route of enantiomerically pure cis-4-amino-3-fluoro-1-methylpiperidine 1 is described. The synthesis features a highly regio-, ...

Nonmetallic doped metal oxides can be broad in their visible-light-response range. However, the half-filled or isolated impurity state can also be the new recombination center for photogenerated electrons/holes, which seriously influence the photocatalytic activity of the catalyst in the visible-light region. Therefore, how to prolong the photogenerated carrier life of nonmetallic doping metal oxides is the difficult and challenging topic in the field of photocatalysis. In this work, the hexagonal nanosheets assembled by N-doped C (N-C)-coated N-doped In2O3 (N-In2O3) nanoparticles (N-C/N-In2O3 HS) was obtained by simply pyrolyzing the In(2,5-PDC) hexagonal sheets. The N-C/N-In2O3 HS catalyst exhibit good photocatalytic activity and cycle stability in the long-wavelength region of visible light (λ = 520 and 595 nm). The effective utilization of long-wavelength visible light for N-C/N-In2O3 HS was mainly attributed to the acceptor-donor-acceptor compensation mechanism between the oxygen vacancy (VO) and substitutional N-doping (Ns) sites, which made the N-C/N-In2O3 HS possess a continuous band structure, without the half-filled or isolated impurity state in the band gap, and extended its light absorption edge to 733 nm. The compensation mechanism of nitrogen doping on In2O3 can promote the photocatalytic activity under longer-wavelength yellow light (595 nm) irradiation. The N-C layer coated on the N-In2O3 nanoparticles acted as a good acceptor of photogenerated electrons, facilitating the effective spatial separation of photogenerated carriers and extend photogenerated carrier lifetimes. The comparative photocatalytic experiments (N-In2O3 HS and N-C/N-In2O3 HS) show that the presence of N-doped C layer can enhance the photocatalytic efficiency by nearly 10-fold. This double-doping and carbon-coating strategy provided a novel research idea to solve the problem that nonmetal atoms doped metal oxides led to the secondary combination of photogenerated electrons/holes.

The low utilization efficiency in the visible region of the sunlight spectrum and the rapid recombination of photogenerated charge carriers are two crucial drawbacks that suppress the practical usage of metal oxide semiconductors as photocatalysts. In this article, we report a rational design of In2O3-In2S3 heterojunctions encapsulated by N-doped carbon with a hollow dodecahedral structure (In2O3-In2S3/N-C HDS), which can effectively handle the two drawbacks of metal oxide semiconductors and behave active for organic transformation under the irradiation of visible light even with long wavelengths. As exemplified by the selective oxidative coupling reaction of amine to imine, the obtained In2O3-In2S3/N-C HDS as the photocatalyst has exhibited excellent activity and stability. Experimental and density functional theory studies have verified that the excellent performance of In2O3-In2S3/N-C HDS can be attributed to the synergistic effect of In2O3-In2S3 heterojunctions, the coating of N-doped carbon, and the hollow porous structure with nanosheets as subunits.

Developing high-efficiency and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is crucial for various energy conversion systems. Herein, N/S co-doped C encapsulated hollow N...

N- and S-doped C-encapsulated CeO2 with a hinge-like nanostructure (CeO2@N,S-C HN) has been obtained by using a Ce-based metal-organic framework (Ce-MOF-808) as a precursor. Due to the synergistic effects of its special structure and N,S-doped C layer, CeO2@N,S-C HN exhibits high activity of photocatalytic hydrogen (H2) evolution. Density functional calculations are used to obtain a fundamental understanding of the high H2 production rate of CeO2@N,S-C HN.

Phosgene, a widely used but highly toxic substance, may pose a serious risk to public safety and health because of the potential abuse and possible accidental leakage. Consequently, it is of great significance to develop a rapid, reliable, and sensitive detection method for this noxious agent. In this work, an aggregation-induced emission-based sensor, 3,6-bis(1,2,2-triphenylvinyl)benzene-1,2-diamine (DATPE), has been rationally designed for detecting phosgene by conjugation of o-phenylenediamine (OPD) core as the reactive recognition moiety decorated with two peripheral triphenylethylene (TPE) units. A light-up fluorescence response is achieved by the fast cyclization reaction of OPD part and phosgene along with the formation of 2-imidazolidinone ring, thus inhibiting the intramolecular charge transfer quenching process in the sensor. Moreover, an easy-to-use test paper with DATPE is fabricated for onsite visual detection of phosgene in the gas phase even at a concentration of as low as 0.1 ppm.

A photoactive triazolobenzothiadiazole (TBTD)-conjugated terphenyldicarboxylate (TPDC) linker was introduced into a porous and robust UiO-68 isoreticular zirconium metal-organic framework (denoted as UiO-68-TBTD) by the de novo synthetic approach of mixed TPDC struts. Under blue-light-emitting-diode irradiation, UiO-68-TBTD can serve as a heterogeneous photocatalyst for the highly efficient and selective oxidation of a sulfur mustard simulant (2-chloroethyl ethyl sulfide) to the corresponding much less toxic sulfoxide product, with a half-life of only 3 min in the open air atmosphere.

The high activity of exposed facets and large surface area have significant effects on the performance of photocatalysts because most of the photoreactivity properties of materials are related to surface processes. The strategy of combining high-index facets and a hollow structure into one material will provide a new way for designing effective photocatalysts, possessing active exposed facets and a large surface area at the same time. However, fabricating one material with both high-index facets and a hollow structure is still a great challenge due to their thermodynamic instability. Here, hollow anatase TiO2 octahedrons exposed with high-index (102) facets (HTO-102) were successfully fabricated for the first time by a facile hydrothermal method using HF and H2O2 as morphology controlling agents. Compared with two other catalysts (a solid sharp octahedron with (101) facets (SSO-101) and a hollow sharp octahedron with (101) facets (HSO-101)), HTO-102 particles exhibit a better photochemical activity for the selective aerobic oxidation of organic sulfides under visible-light irradiation. Experimental results and theoretical calculations indicate that the excellent photocatalytic activity of HTO-102 particles is mainly due to the synergistic effects of its hollow structure and exposed high-index (102) facets.

An efficient photocatalyst should maximize utilization of sunlight and minimize recombination of photogenerated electron–hole pairs. Thus, searching for a simple approach to develop low-cost efficient photocatalysts to improve the utilization ratio of sunlight and boost the photogenerated charge carrier lifetime is very important and challenging. In this article, anchoring Cu2O nanoparticles (NPs) in situ on a nitrogen-doped porous carbon yolk–shell cuboctahedral (CNPC) framework has been successfully carried out by direct derivation from a benzimidazole-modified Cu-btc MOF (btc = benzene-1,3,5-tricarboxylate, MOF = metal–organic framework) template. The prepared CNPC showed high photoredox catalysis in forming C–C bond reactions, resulting from the prolonged lifetime of photogenerated electrons and holes, multiple reflections of light by the yolk–shell structure, and improved stability and dispersibility of Cu2O NPs. Our study provided a simple way to designing low-cost, efficient heterostuctured photoca...

An efficient and practical synthesis of enantiomerically pure P-chiral dihydrobenzooxaphosphole (BOP) core 1 is developed that is amenable to large scale preparation of the related ligand series. The unique epimerization of the P-chiral center of the undesired (R,R)-diastereomeric phosphine oxide 19 through chlorination followed by crystallization makes this chemical resolution method achieve 65% yield of desired (R,S)-diastereomer 12.

The targeted delivery of a photosensitizer (PS) into specific cancer cells is an effective way to enhance the efficacy and minimize the side effects of photodynamic therapy. Herein, heptamannosylated β-cyclodextrin (β-CD) was used to mediate the formation of an adamantane (Ad)-functionalized BODIPY PS nanoparticle via strong β-CD/Ad complexation. The mannose-functionalized PS nanoparticles are selectively internalized by mannose-receptor-rich MDA-MB-231 breast cancer cells via receptor-mediated endocytosis, facilitating singlet oxygen generation to trigger apoptosis in cancer cells upon red-light irradiation. These nanoparticles exhibit excellent targeted delivery of the PS, leading to cancer cell death after irradiation both in vitro and in vivo.

A highly porous metal-organic framework (MOF) incorporating both exposed metal sites and nitrogen-rich triazole groups was successfully constructed via solvothermal assembly of a clicked octcarboxylate ligand and Cu(II) ions, which presents a high affinity toward CO2 molecules clearly verified by gas adsorption and Raman spectral detection. The constructed MOF featuring CO2-adsorbing property and exposed Lewis-acid metal sites could serve as an excellent catalyst for CO2-based chemical fixation. Catalytic activity of the MOF was confirmed by remarkably high efficiency on CO2 cycloaddition with small epoxides. When extending the substrates to larger ones, its activity showed a sharp decrease. These observations reveal that MOF-catalyzed CO2 cycloaddition of small substrates was carried out within the framework, while large ones cannot easily enter into the porous framework for catalytic reactions. Thus, the synthesized MOF exhibits high catalytic selectivity to different substrates on account of the confinement of the pore diameter. The high efficiency and size-dependent selectivity toward small epoxides on catalytic CO2 cycloaddition make this MOF a promising heterogeneous catalyst for carbon fixation.

As an extension of nitride luminescent materials, carbidonitride phosphors are also attracting great attention due to their superior thermal stability. This paper reports a blue-emitting carbidonitride phosphor Al1–xSixCxN1–x:Eu2+ suitable for near ultraviolet (UV) light emitting diodes (LEDs), which is formulated by introducing SiC into AlN:Eu2+. With the introduction of carbon (silicon), the lattice abnormally shrinks along both a- and c-axes at low x values (x ≤ 0.08), due to the formation of a dense interlayer for accommodating the luminescence center Eu2+. Both of the Raman spectra and solid state NMR spectroscopy show that both Si and C are dissolved in the AlN lattice. A single blue emission band (λem = 472–477 nm) is observed for compositions of x > 0.05 by cathodoluminescence measurements. Under the 365 nm excitation, the maximum luminescence is attained for the composition of x = 0.06 that has an external quantum efficiency of 61% and absorption efficiency of 74.4%, which is about 11–15% higher ...

The single-particle-diagnosis approach allows for the fast discovery of novel luminescent materials using powdered samples. This paper reports a new blue-emitting Sr3Si8–xAlxO7+xN8–x:Eu2+ phosphor for solid state lighting and its scale-up synthesis. The structure-, composition-, and temperature-dependent luminescence were investigated and discussed by means of various analytic techniques including single-crystal XRD diffractometer, single-particle fluorescence spectroscopy, FTIR spectra, decay time, low-temperature luminescence, and computed energy level scheme. Sr3Si8–xAlxO7+xN8–x crystallizes in the monoclinic system (space group C2/c, no. 15) with a = 18.1828 (13) A, b = 4.9721 (4) A, c = 15.9557 (12) A, β = 115.994 (10)ο, and Z = 2. The Sr atoms are coordinated to 8 and 6 O/N atoms and located in the voids along [010] formed by vertex-sharing (Si,Al)-(O,N)4 tetrahedra. Phase-pure powder samples of Sr3Si8–xAlxO7+xN8–x:Eu2+ were synthesized from the chemical composition of the single particle by control...

We report an experimental observation of aggregation-induced enhanced luminescence upon three-photon excitation in aggregates formed from a class of unsymmetrical cyanostilbene derivatives. Changing side chains (-CH3, -C6H13, -C7H15O3, and folic acid) attached to the cyanostilbene core leads to instantaneous formation of aggregates with sizes ranging from micrometer to nanometer scale in aqueous conditions. The crystal structure of a derivative with a methyl side chain reveals the planarization in the unsymmetrical cyanostilbene core, causing luminescence from corresponding aggregates upon three-photon excitation. Furthermore, folic acid attached cyanostilbene forms well-dispersed spherical nanoaggregates that show a high three-photon cross-section of 6.0 × 10(-80) cm(6) s(2) photon(-2) and high luminescence quantum yield in water. In order to demonstrate the targeted bioimaging capability of the nanoaggregates, three cell lines (HEK293 healthy cell line, MCF7 cancerous cell line, and HeLa cancerous cell line) were employed for the investigations on the basis of their different folate receptor expression level. Two kinds of nanoaggregates with and without the folic acid targeting ligand were chosen for three-photon bioimaging studies. The cell viability of three types of cells incubated with high concentration of nanoaggregates still remained above 70% after 24 h. It was observed that the nanoaggregates without the folic acid unit could not undergo the endocytosis by both healthy and cancerous cell lines. No obvious endocytosis of folic acid attached nanoaggregates was observed from the HEK293 and MCF7 cell lines having a low expression of the folate receptor. Interestingly, a significant amount of endocytosis and internalization of folic acid attached nanoaggregates was observed from HeLa cells with a high expression of the folate receptor under three-photon excitation, indicating targeted bioimaging of folic acid attached nanoaggregates to the cancer cell line. This study presents a paradigm of using organic nanoaggregates for targeted three-photon bioimaging.

An efficient production synthesis of the SGLT-2 inhibitor Empagliflozin (5) from acid 1 is described. The key tactical stage involves I/Mg exchange of aryl iodide 2 followed by addition to glucono lactone 3 in THF. Subsequent in situ treatment of the resulting lactol with HCl in MeOH produces β-anomeric methyl glycopyranoside 4 which is, without isolation, directly reduced with Et3SiH mediated by AlCl3 as a Lewis acid in CH2Cl2/MeCN to afford 5 in 50% overall yield. The process was implemented for production on a metric ton scale for commercial launch.

The design and construction of novel artificial molecular machines can be categorized as a currently important field of modern chemistry. In the present work, a novel photoresponsive [3]rotaxane containing two cucurbit[7]uril (CB[7]) rings and a dumbbell component consisting of one trans-azobenzene unit along with two viologen units was developed. Each viologen group was encircled by a CB[7] ring with a rapid shuttling equilibration distribution extended to the trans-azobenzene unit located in the middle of the dumbbell component. Upon the trans-to-cis photoisomerization of the azobenzene unit under UV light irradiation, a shuttling restriction of the CB[7] rings along the dumbbell component was observed. The equilibration distribution of the macrocycles on the dumbbell component can be recovered by the cis-to-trans photoisomerization of the azobenzene unit under visible light irradiation. Such a controllable shuttling process was fully characterized by (1)H NMR spectroscopy and was easily indicated by fluorescent changes of the [3]rotaxane.

Poly(butylene succinate) (PBS)/graphene oxide (GO) nanocomposites were facilely prepared via in situ polymerization. The properties of the nanocomposites were studied using FTIR, XRD, and (1)H NMR, and the state of dispersion of GO in the PBS matrix was examined by SEM. The crystallization and melting behavior of the PBS matrix in the presence of dispersed GO nanosheets have been studied by DSC and polarized optical microscopy. Through the mechnical testing machine and DMA, PBS/GO nanocomposites with 3% GO have shown a 43% increase in tensile strength and a 45% improvement in storage modulus. This high performance of the nanocomposites is mainly attributed to the high strength of graphene oxide combined with the strong interfacial interactions in the uniformly dispersed PBS/GO nanocomposites.

A convergent synthesis of NNRTI 1 is described. The key step involves a direct coupling of acid chloride 4 with Grignard reagent 11 in the presence of bis[2-(N,N-dimethylamino)ethyl] ether that moderates the reactivity of the Grignard reagent to give benzophenone 7. An efficient 2-step process for the preparation of 2-fluoro-3-methyl-4-aminobenzoic acid (3) is also described.

The synthesis of LFA-1 inhibitor BIRT2584 on metric-ton scale was accomplished by means of a safe and robust process. Highlights of the process include the asymmetric synthesis of the key advanced intermediate by implementation of Seebach’s self-regeneration of stereocenters principle, and a Ph3PCl2-induced dehydration of a critical urea followed by a regioselective bromination to give the elaborated 1H-imidazo[1,2-a]imidazol-2-one. A sulfonyl chloride intermediate was produced through Br/Mg exchange of iodoimidazole followed by addition to SO2 in THF and subsequent oxidation. In a one-pot operation, the sulfonyl chloride was directly reacted with l-alaninamide using NaOH as base in aqueous DMF/THF to give BIRT2584.

An electroactive tetrathiafulvalene (TTF)-functionalized amphiphile 1 was designed and synthesized to investigate its self-assembling behavior in water. Dynamic light scattering (DLS), (1)H NMR, fluorescence spectrum, and cryogenic transmission electron microscopy (cryo-TEM) studies revealed that amphiphile 1 can form micelle-like aggregates via direct dissolution into water, and the micellar architectures could be disrupted either by addition of chemical oxidant Fe(ClO(4))(3) or by complexation with electron-deficient cyclobis(paraquat-p-phenylene) tetracation cyclophane (CBPQT(4+)) to release encapsulated hydrophobic dye Nile Red from the interior of micelles.

Reaction of 4-bromo-NH-1,2,3-triazoles 2 with alkyl halides in the presence of K(2)CO(3) in DMF produced the corresponding 2-substituted 4-bromo-1,2,3-triazoles 5 in a regioselective process. Subsequent Suzuki cross-coupling reaction of these bromides provided an efficient synthesis of 2,4,5-trisubstituted triazoles 3. In addition, reduction of the bromotriazoles by hydrogenation furnished an efficient synthesis of 2,4-disubstituted triazoles 8.

A one-pot process for the synthesis of (S)-1,1,1-trifluoro-4-(5-fluoro-2-methoxy-phenyl)-4-methyl-2-((R)-toluene-4-sulfinylmethyl)pentan-2-ol (3) is described, which was a key intermediate for the preparation of a class of novel glucocorticoid receptor ligands. The chemistry features the preparative-scale synthesis of (R)-p-tolyl methyl sulfoxide [(R)-pTMSO] from (2R,4S,5R)-4-methyl-5-phenyl-3-(tolene-4-sulfonyl)oxathiazolidine-2-oxide (5) and the synthesis of 3 from 5 without isolation of (R)-pTMSO during the process.

A new procedure for the practical synthesis of (S)-2-(cyclopentyloxycarbonyl)amino-8-nonenoic acid, a key building block for BILN 2061, an HCV NS3 protease inhibitor, has been developed. The key step features a kinetic resolution of racemic 2-acetylamino-8-nonenoic acid with acylase I. In addition, the undesired (R)-2-acetylamino-8-nonenoic acid was recycled after racemization. The procedure was implemented for the production of (S)-2-(cyclopentyloxycarbonyl)amino-8-nonenoic acid on pilot-plant scale.

A multistep scalable synthesis of the clinically important hepatitis C virus (HCV) protease inhibitor BILN 2061 (1) is described. The synthesis is highly convergent and consists of two amide bond formations, one etherification, and one ring-closing metathesis (RCM) step, using readily available building blocks 2−5. The optimization of each step is described at length. The main focus of the paper is the study of the RCM step and the description of the main problems faced when scaling up to pilot scale this highly powerful but very challenging synthetic operation. Eventually, the RCM reaction was smoothly scaled up to produce >400 kg of cyclized product.

(1R,2S)-1-Amino-2-vinylcyclopropanecarboxylic acid (vinyl-ACCA) is a key building block in the synthesis of potent inhibitors of the hepatitis C virus NS3 protease such as BILN 2061, which was recently shown to dramatically reduce viral load after administration to patients infected with HCV genotype 1. We have developed a scalable process that delivers derivatives of this unusual amino acid in99% ee. The strategy was based on the dialkylation of a glycine Schiff base using trans-1,4-dibromo-2-butene as an electrophile to produce racemic vinyl-ACCA, which was subsequently resolved using a readily available, inexpensive esterase enzyme (Alcalase 2.4L). Factors that affect diastereoselection in the initial dialkylation steps were examined and the conditions optimized to deliver the desired diastereomer selectively. Product inhibition, which was encountered during the enzymatic resolution step, initially resulted in prolonged cycle times. Enrichment of racemic vinyl-ACCA through a chemical resolution via diastereomeric salt formation or the use of forcing conditions in the enzymatic reaction both led to improvements in throughput and the development of a viable process. The chemistry described herein was scaled up to produce multikilogram quantities of this building block.

Reaction of 4,5-dibromo-1,2,3-triazole with electron-deficient aromatic halides in the presence of potassium carbonate in DMF produces the corresponding 2-aryl-4,5-dibromotriazoles with high regioselectivity. Subsequent debromination of these triazoles by hydrogenation furnishes 2-aryltriazoles in excellent yields. Overall, this two-step process provides an efficient access to 2-aryl-1,2,3-triazoles.

[reaction: see text] Iodo- and bromoaromatics bearing sensitive carboxylic ester and cyano groups underwent a selective halide-magnesium exchange with isopropylmagnesium chloride at ambient temperature in the presence of bis[2-(N,N-dimethylamino)ethyl] ether to afford the corresponding Grignard reagents. The newly formed reactive Grignard reagents were allowed to react with electrophiles such as trimethylborate to afford arylboronic acids in good to excellent yields.

A new approach to 2,5-bridged furanocyclic compounds was demonstrated for rings of 12-14 members. Accordingly, allenylstannyl aldehydes 1.16, 2.11, 3.12a, 3.12b, 4.12, 5.15, and 6.12, upon treatment with BF 3 .OEt 2 at -78 o C, smoothly cyclized to the homopropargylic alcohols 1.17, 2.12, 3.13a, 3.13b, 4.13, 5.16, and 6.13 in 87-94% yield. Oxidation and basic isomerization afforded the allenones 1.19, 2.14, 3.15a, 3.15b, 4.14, 5.18, and 6.15 in high yield. Intraannular cyclization to the furanocycles 1.21, 2.15, 3.16a, 3.16b, 4.16, 5.19, and 6.16 was effected with catalytic AgNO 3 and CaCO 3 in aqueous acetone

3-Alkoxylmethyl-5-alkylpyrazoles undergo regioselective N-arylation with 4-fluoronitrobenzene in the presence of base to yield the corresponding 1-(4-nitro-phenyl)pyrazoles. Further elaboration of these intermediates furnishes a practical synthesis of unsymmetrical 3,5-dialkyl-1-arypyrazoles. A tentative explanation of the observed regioselectivities is provided.

Optically active (R)-(propargyloxy) acetic esters 5, available in ca. 90% ee through reduction of alkynones 2 with Chirald-LiAlH 4 followed by alkylation with chloroacetic acid and esterification with CH 2 N 2 , undergo highly stereoselective [2,3] rearrangement upon treatment with LDA in THF at −78 o C followed by Cp 2 ZrCl 2 to afford α(S)-hydroxy-β(R)-allenic esters 7 with complete transfer of chirality and >90% diastereoselectivity. Upon treatment with TESOTf in Et 3 N the (R)-(propargyloxy) acetic esters 5 afford the diastereomeric α-(R)-hydroxy-β-(R)-allenic esters 8 stereoselectively. Both hydroxy esters 7 and 8 cyclize stereospecifically to trans- and cis-2,5-dihydrofurans 13-15 and 17-19 upon treatment with AgNO 3 -CaCO 3 , PhSeCl, or NBS

W(CO) 6 -mediated intramolecular desulfurdimerization reactions have been used in the syntheses of bridged 2,2'-disubstituted bifluorenylidenes in satisfactory yields. Ring sizes from 12 to 24 can be synthesized by this reaction. The extension of this reaction for the synthesis of bifluorenylidene-hinged crown ethers is described. The X-ray structure of 6i has been determined. The two fluorenylidene moieties are each planar, making a dihedral angle of 44.9°. The first optically active bifluorenylidenes were unequivocally synthesized, and the barriers for the racemization of two such molecules have been determined (12 kcal/mol)

The BF 3 -promoted addition of (S)-allenylstannane (S)-6 to aldehyde afforded a 68:32 mixture of diastereometic homopropargylic alcohols 17 and 18 whereas MgBr 2 -promoted addition gave adduct 17 as the exclusive product. The (R)-allenylstannane (R)-6, on the other hand, yielded a 30:1 mixture of syn anti alcohol adducts 19 and 20 with BF 3 •OEt 2 and 1:92 mixture favoring the anti addult 20 under MgBr 2 catalysis

The allenylstannane 4 undergoes highly syn selective additions to α-branched aldehydes 8b and 8c in the presence of BF 3 .OEt 2 . With the β-alkoxy aldehyde 21, Cram-Felkin addition results with BF 3 .OEt 2 as the Lewis acid, whereas MgBr 2 leads to chelation-controlled addition

Optically active propargyloxyacetic acids 4, available in ca. 90% ee through reduction of alkynones 2 with Chirald-LiAlH 4 followed by alkylation with chloroacetic acid, undergo highly stereoselective [2,3] rearrangement upon treatment with LDA in THF at -78°C to afford α-(S)-hydroxy-β-(R)-allenic acids with complete transfer of chirality and > 90% diastereoselectivity. The diastereomeric methyl ester derivatives 5a and 13 cyclize stereospecifically to trans and cis 1,5-dihydrofurans upon treatment with AgNO 3 -CaCO 3 , PhSeCl, or NBS

Reactions de desulfuration et de dimerisation de sulfures organiques ou de reduction chimique de thiols