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A Sc(OTf)3-catalyzed formal acylcyanation of electron-rich alkynes for the efficient synthesis of fully-substituted acrylonitriles is described. By means of alkyne carbonyl metathesis, the reaction features mild conditions, high regio- and stereoselectivity, and a broad scope. The strong preference of the nitrile group for inward rotation in the torquoselective ring opening of the oxetane intermediate determines the remarkable Z selectivity of this process. [ABSTRACT FROM AUTHOR]

A dielectric barrier discharge in a corona process configuration is used to treat the surface of fluoropolymers in a nitrogen-organic precursor environment. The surface chemistry, thickness, and water contact angle of the deposited coatings are measured and used to build up an output matrix to be correlated with an input matrix built using electrical parameters of the discharge, the gas mixture chemical composition, and spectroscopic parameters measured in both the infrared and ultraviolet-visible emission spectral regions. A partial least-squares regression (PLSR) model enables determining the most important plasma parameters to drive the coating physicochemical characteristics. From the PLSR model, it is determined that the plasma electrical parameters drive the surface modification process, at the expense of other plasma characteristics such as gas flow, gaseous precursor concentration, nitrogen vibrational temperature, and the level of gaseous precursor conversion within the plasma. [ABSTRACT FROM AUTHOR]

A synthetic strategy for accessing protoaculeine B (1), the N-terminal amino acid of the highly modified peptide toxin aculeine, was developed via the synthesis of the fully protected natural homologue of 1 with a 12-mer poly(propanediamine). The synthesis of mono(propanediamine) analog 2, as well as core amino acid 3, was demonstrated by this strategy. New amino acid 3 induced convulsions in mice; however, compound 2 showed no such activity. [ABSTRACT FROM AUTHOR]

A facile, general, and economical synthesis of diversely functionalized pyrimidines has been realized under basic conditions via the copper-catalyzed cyclization of ketones with nitriles. The reaction proceeds via a novel pathway involving the nitriles acting as electrophiles and consecutive C–C bond and two C–N bond formations and shows broad substrate scope and good tolerance of many important functional groups. This strategy represents a new platform for constructing pyrimidine structures. [ABSTRACT FROM AUTHOR]

o-Phenylene tetramers have been coassembled with linkers into macrocycles through imine condensation. Variation of linker connectivity and length allows both [1 + 1] and [2 + 2] macrocycles to be obtained, complementing (previously reported) [3 + 3] macrocycles. For the [1 + 1] macrocycles, linker length has a clear effect on o-phenylene geometry and macrocycle stability. For the [2 + 2] macrocycles, both homo- and heterochiral configurations are observed, suggesting limited communication of helix handedness in these systems. [ABSTRACT FROM AUTHOR]

An efficient nickel-promoted selective monocyanation of benzamides with TMSCN via 8-aminoquinoline directed ortho C–H activation has been developed. Varieties of functionalized ortho-cyanated (hetero)aryl nitriles can be selectively synthesized in moderate to good yields. These cyanation products can be easily transformed into various 3-imino-1-oxoisoindolines in a one-pot procedure. The mild reaction conditions, use of cheap and commercially available reagents, wide functional group tolerance, and operational convenience make this protocol practical to the synthetic community. [ABSTRACT FROM AUTHOR]

The vinyl ether benzyloxycarbonyl (VeZ) protecting group is selectively cleaved by treatment with tetrazines via an inverse electron-demand Diels–Alder reaction. This represents a new orthogonal protecting group for solid-phase peptide synthesis, with Fmoc-Lys(VeZ)-OH as a versatile alternative to Fmoc-Lys(Alloc)-OH and Fmoc-Lys(Dde)-OH, as demonstrated by the synthesis of two biologically relevant cyclic peptides. [ABSTRACT FROM AUTHOR]

o-Nitrobenzyl (oNB) derivatives are widely used photolabile caged compounds in chemical and biological applications. The primary step in the photoinduced deprotection is an excited state intramolecular hydrogen transfer (ESIHT) leading to tautomerization of the oNB compound and subsequent release of the protecting group. The prototype molecule for studying such ESIHT is o-nitrotoluene (oNT), where hydrogen transfers from the methyl to the nitro group. Using the complete active space self-consistent field (CASSCF) method with second-order perturbative energy corrections (CASPT2), we have comprehensively investigated the photoisomerization and photo decay mechanisms in oNT. We have obtained the minimum energy crossing points (MECPs) between relevant electronic states and identified the singlet and triplet pathways. There is a barrierless path for oNT to relax to the lowest triplet state. In this T1 state, the ESIHT products are more stable than T1 oNT. Hydrogen-transfer occurs on the T1 state followed by relaxation to the ground state to give the isomerized product. A biradical intermediate proposed by previous studies is characterized to be the hydrogen-transferred T1 product. On the singlet pathway, in contrast to the triplet, the ground state tautomer is formed from the S1 oNT through a geometrically distant and energetically higher S1/S0 conical intersection. Although nonadiabatic dynamical studies are essential for determining branching ratios, our study, which considers the accessibility of different MECPs based on geometry and energy, and the magnitude of spin-orbit coupling at singlet-triplet MECPs, suggests that a significant fraction of the isomerization yield is due to the triplet channel. [ABSTRACT FROM AUTHOR]

A formal [3 + 3] cycloaddition reaction between azides and in situ formed azaoxyallyl cations has been realized. This reaction provided an efficient and practical pathway to synthesize 1,2,3,4-tetrazines in good yields under mild conditions. Biologically active molecules could also be well compatible, highlighting the potential value of this reaction. [ABSTRACT FROM AUTHOR]

Rh (III)-catalyzed C–H activation of benzoylacetonitriles in coupling with diazo compounds was developed to synthesize diversified substituted benzo[de]chromenes via a formal (4 + 2) cycloaddition with a diazo compound and subsequent tandem (4 + 2) cycloaddition with another diazo compound. Intriguingly, synthesis of substituted benzo[de]chromenes and their decarboxylation products could be realized by controlling the reaction conditions. These reactions have a broad range of substrates, moderate to good yields, and high regioselectivity. [ABSTRACT FROM AUTHOR]

The carbazochrome (3) solubility in solvent mixtures of DMF (N,N-dimethylformamide, 1) + methanol (2), DMF (1) + ethanol (2), DMF (1) + n-propanol (2), and dimethyl sulfoxide (DMSO, 1) + water (2) was measured by the static method within the temperature range from (278.15 to 318.15) K under atmospheric pressure, p = 101.0 kPa. The solubility of carbazochrome increased with rising mass fraction of DMF or DMSO and temperature. The Jouyban-Acree, van't Hoff-Jouyban-Acree, and Apelblat-Jouyban-Acree models were used to correlate the obtained solubility, and the Apelblat-Jouyban-Acree model provided better correlation results. The parameters of preferential solvation (δx1,3) were acquired from the mixture properties with the method of inverse Kirkwood-Buff integrals. The values of δx1,3 changed nonlinearly with the DMF/DMSO (1) proportion in the studied mixed solvents. The carbazochrome was solvated preferentially by alcohol or water in alcohol or water-rich solutions and preferentially solvated by DMF/DMSO in DMF/DMSO-rich mixtures. It could be speculated that in DMF/DMSO-rich mixtures the interaction by acidic hydrogen bonding with the basic sites of carbazochrome played a significant role in carbazochrome solvation. [ABSTRACT FROM AUTHOR]

Dissolved organic nitrogen (DON) comprises the largest pool of fixed N in the surface ocean, yet its composition has remained poorly constrained. Knowledge of the chemical composition of this nitrogen pool is crucial for understanding its biogeochemical function and reactivity in the environment. Previous work has suggested that high-molecular-weight (high-MW) DON exists only in two closely related forms, the secondary amides of peptides and of N-acetylated hexose sugars. Here, we demonstrate that the chemical structures of high-MW DON may be much more diverse than previously thought We couple isotopic labeling of cyanobacterially derived dissolved organic matter with advanced two-dimensional NMR spectroscopy to open the “black box” of uncharacterized high-MW DON. Using multibond NMR correlations, we have identified novel N-methyl-containing amines and amides, primary amides, and novel N-acetylated sugars, which together account for nearly 50% of cyanobacterially derived high- MW DON. This study reveals unprecedented compositional details of the previously uncharacterized DON pool and outlines the means to further advance our understanding of this biogeochemically and globally important reservoir of organic nitrogen. [ABSTRACT FROM AUTHOR]

Two prenyltransferases from Aspergillus ruber control the echinulin biosynthesis via exceptional sequential prenylations. EchPT1 catalyzes the first prenylation step, leading to preechinulin. The unique EchPT2 attaches, in a consecutive prenylation cascade, up to three dimethylallyl moieties to preechinulin and its dehydro forms neoechinulins A and B, resulting in the formation of at least 23 2- to 4-fold prenylated derivatives. Confirming these products in fungal extracts unravels the unprecedented catalytic relevance of EchPT2 for structural diversity. [ABSTRACT FROM AUTHOR]

A regioselective zincation of the 2-pyridone and 2,7-naphthyridone scaffolds has been developed. Zincations of the methoxyethoxymethyl (MEM)-protected compounds using TMP2Zn•2MgCl2•2LiCl (TMP = 2,2,6,6-tetramethylpiperidyl) followed by trapping with electrophiles provided functionalized 2-pyridones and 2,7-naphthyridones. I/Mg exchange of iodinated 2-pyridone and 2,7-naphthyridone using i-PrMgCl•LiCl afforded magnesiated intermediates that reacted with electrophiles. A second magnesiation of the 2-pyridone scaffold was achieved by using TMPMgCl•LiCl. Additionally, we report CoCl2-catalyzed cross-couplings of the 1-chloro-2,7-naphthyridines with arylzinc halides. [ABSTRACT FROM AUTHOR]

Covalent cross-links are crucial for the folding and stability of triple-helical collagen, the most abundant protein in nature. Cross-linking is also an attractive strategy for the development of synthetic collagen-based biocompatible materials. Nature uses interchain disulfide bridges to stabilize collagen trimers. However, their implementation into synthetic collagen is difficult and requires the replacement of the canonical amino acids (4R)-hydroxyproline and proline by cysteine or homocysteine, which reduces the preorganization and thereby stability of collagen triple helices. We therefore explored alternative covalent cross-links that allow for connecting triple-helical collagen via proline residues. Here, we present collagen model peptides that are cross-linked by oxime bonds between 4-aminooxyproline (Aop) and 4-oxoacetamidoproline placed in coplanar Xaa and Yaa positions of neighboring strands. The covalently connected strands folded into hyperstable collagen triple helices (Tm ≈ 80 °C). The design of the cross-links was guided by an analysis of the conformational properties of Aop, studies on the stability and functionalization of Aop-containing collagen triple helices, and molecular dynamics simulations. The studies also show that the aminooxy group exerts a stereoelectronic effect comparable to fluorine and introduce oxime ligation as a tool for the functionalization of synthetic collagen. [ABSTRACT FROM AUTHOR]

Lycoplanine A (1), a Lycopodium alkaloid with a 6/9/5 tricyclic ring skeleton fused with the γ-lactone ring and featuring an unusual 1-oxa-6-azaspiro[4.4]nonane moiety and an unprecedented 3-azabicyclo[6.3.1]dodecane unit, was isolated from the club moss Lycopodium complanatum. The structure and absolute configuration of 1 were identified by a combination of NMR spectroscopic analysis and single-crystal X-ray diffraction. Biological studies showed that 1 is a potent Cav3.1 T-type calcium channel (TTCC) inhibitor with an IC50 value of 6.06 μM. [ABSTRACT FROM AUTHOR]

A novel and efficient approach toward the assembly of the synthetically challenging tetracyclic [6,5,7,5] core structure of calyciphylline A-type alkaloids is developed. The synthetic route features a tandem semipinacol rearrangement/Nicholas reaction that has been devised strategically to construct the spirocyclic A/B ring and the sterically congested vicinal all-carbon quaternary carbon centers in high diastereoselectivity. Late-stage installation of the hydropyrrole ring and the strained 7-membered ring via a double-reductive amination and ring-closing metathesis, respectively, has also been realized. [ABSTRACT FROM AUTHOR]

A synthetic strategy to access the fused 6-7-6 tricyclic core of hetisine-type C20-diterpenoid alkaloids is reported. This strategy employs a Diels-Alder cycloaddition to assemble a fused bicyclic anhydride intermediate, which is elaborated to a vinyl lactone-acetal bearing an aromatic ring in five steps. Aromatic iodination is followed by magnesium-halogen exchange with a trialkyl magnesiate species, which undergoes intramolecular cyclization. Subsequent oxidation provides the desired 6-7-6 tricyclic diketoaldehyde, with carbonyl groups at all three positions for eventual C-N bond formation and subsequent elaboration. [ABSTRACT FROM AUTHOR]

2-Amino-3-arylindoles were conveniently prepared from 3-diazoindolin-2-imines and arylboronic acids through palladium carbene intermediates in moderate to excellent yields. The synthesized 2-amino-3-arylindoles could be fluorinated with NFSI to afford 3-aryl-3-fluoroindolin-2-imines. [ABSTRACT FROM AUTHOR]

Lycopodium alkaloids with structural diversity and biological significance have been stimulating an increasing interest in the synthetic and medicinal communities, in which inspiration and exploration of their related biogenetic relationship generally constitute one of the major concerns. Driven by the plausible biogenetic entry to lycojaponicumin D as the first member of Lycopodium alkaloids having a structurally unusual C3-C13-linked scaffold, a new connection with lycodoline has been proposed and discovered on the basis of the design of an unprecedented bioinspired tandem fragmentation/Mannich reaction. Initiated by expeditious assembly of bridgehead heterofunctionalization in the [3.3.1] bicyclic system of lycodoline, a novel tandem palladium-mediated oxidative dehydrogenation/hetero- Michael reaction has been developed for the strain-driven formation of the C-heteroatom bond, leading to a new approach to conformationally rigid bridgehead heteroquaternary carbons. The present unified strategy provides a scenario for the divergent total syntheses of nine natural Lycopodium alkaloids and four unnatural C12 epimers, wherein (±)-lycojaponicumin D and six lycodoline-type alkaloids have been synthetically achieved for the first time. [ABSTRACT FROM AUTHOR]

A unique approach to gliocladin C and related alkaloids was developed that features an unprecedented nucleophilic addition of a diketopiperazine to an isatin derivative followed by a Friedel-Crafts alkylation of the resultant tertiary alcohol with indole to set the key quaternary center. Chemoselective oxindole reduction and cyclization delivered a pivotal hexahydropyrrolo[2,3-b]indole diketopiperazine intermediate that was readily converted into (±)-gliocladin C, (±)-T988C, and (±)-gliocladine C, culminating in the shortest approach to these alkaloids reported to date. [ABSTRACT FROM AUTHOR]

Amino acids constitute an important fraction of the water-soluble organic nitrogen (WSON) compounds in aerosols and are involved in many processes in the atmosphere. In this work, we applied X-ray photoelectron spectroscopy (XPS) to study aqueous solutions of four amino acids, glycine, alanine, valine, and methionine, in their zwitterionic forms. We found that amino acids with hydrophilic side chains and smaller size, GLY and ALA, tend to stay in the bulk of the liquid, while the hydrophobic and bigger amino acids, VAL and MET, are found to concentrate more on the surface. We found experimental evidence that the amino acids have preferential orientation relative to the surface, with the hydrophobic side chain being closer to the surface than the hydrophilic carboxylate group. The observed amino acid surface propensity has implications in atmospheric science as the surface interactions play a central role in cloud droplet formation, and they should be considered in climate models. [ABSTRACT FROM AUTHOR]

Density functional theory investigations revealed that the pyridine-boryl radical generated in situ using 4-cyanopyridine and bis(pinacolato)diboron could be used as a bifunctional "reagent", which serves as not only a pyridine precursor but also a boryl radical. With the unique reactivity of such radicals, 4-substituted pyridine derivatives could be synthesized using α,β-unsaturated ketones and 4-cyanopyridine via a novel radical addition/C C coupling mechanism. Several controlled experiments were conducted to provide supportive evidence for the proposed mechanism. In addition to enones, the scope could be extended to a wide range of boryl radical acceptors, including various aldehydes and ketones, aryl imines and alkynones. Lastly, this transformation was applied in the late-stage modification of a complicated pharmaceutical molecule. [ABSTRACT FROM AUTHOR]

Cysteinate oxygenation is intimately tied to the function of both cysteine dioxygenases (CDOs) and nitrile hydratases (NHases), and yet the mechanisms by which sulfurs are oxidized by these enzymes are unknown, in part because intermediates have yet to be observed. Herein, we report a five-coordinate bis-thiolate ligated Fe(III) complex, [FeIII(S2Me2N3(Pr,Pr))]+ (2), that reacts with oxo atom donors (PhIO, IBX-ester, and H2O2) to afford a rare example of a singly oxygenated sulfenate, [FeIII(η²-SMe2O)(SMe2)N3(Pr,Pr)]+ (5), resembling both a proposed intermediate in the CDO catalytic cycle and the essential NHase Fe-S(O)Cys114 proposed to be intimately involved in nitrile hydrolysis. Comparison of the reactivity of 2 with that of a more electron-rich, crystallographically characterized derivative, [FeIIIS2Me2NMeN2amide(Pr,Pr)]- (8), shows that oxo atom donor reactivity correlates with the metal ion's ability to bind exogenous ligands. Density functional theory calculations suggest that the mechanism of S-oxygenation does not proceed via direct attack at the thiolate sulfurs; the average spin-density on the thiolate sulfurs is approximately the same for 2 and 8, and Mulliken charges on the sulfurs of 8 are roughly twice those of 2, implying that 8 should be more susceptible to sulfur oxidation. Carboxamide-ligated 8 is shown to be unreactive towards oxo atom donors, in contrast to imine-ligated 2. Azide (N3-) is shown to inhibit sulfur oxidation with 2, and a green intermediate is observed, which then slowly converts to sulfenate-ligated 5. This suggests that the mechanism of sulfur oxidation involves initial coordination of the oxo atom donor to the metal ion. Whether the green intermediate is an oxo atom donor adduct, Fe-O-I-Ph, or an Fe(V)-O remains to be determined. [ABSTRACT FROM AUTHOR]

Rapid bioorthogonal reactivity can be induced by controllable, catalytic stimuli using air as the oxidant. Methylene blue (4 µM) irradiated with red light (660 nm) catalyzes the rapid oxidation of a dihydrotetrazine to a tetrazine thereby turning on reactivity toward trans-cyclooctene dienophiles. Alternately, the aerial oxidation of dihydrotetrazines can be efficiently catalyzed by nanomolar levels of horseradish peroxidase under peroxide-free conditions. Selection of dihydrotetrazine/tetrazine pairs of sufficient kinetic stability in aerobic aqueous solutions is key to the success of these approaches. In this work, polymer fibers carrying latent dihydrotetrazines were catalytically activated and covalently modified by trans-cyclooctene conjugates of small molecules, peptides, and proteins. In addition to visualization with fluorophores, fibers conjugated to a cell adhesive peptide exhibited a dramatically increased ability to mediate contact guidance of cells. [ABSTRACT FROM AUTHOR]

Herein we report an atom- and step-economic aromatic cyanoalkylation reaction that employs nitriles as building blocks and proceeds through Csp²--H and Csp³--H bond activation steps mediated by NiIII. In addition to cyanomethylation with MeCN, regioselective α-cyanoalkylation was observed with various nitrile substrates to generate secondary and tertiary nitriles. Importantly, to the best of our knowledge these are the first examples of C--H bond activation reactions occurring at a NiIII center, which may exhibit different reactivity and selectivity profiles than those corresponding to analogous NiII centers. These studies provide guiding principles to design catalytic C--H activation and functionalization reactions involving high-valent Ni species. [ABSTRACT FROM AUTHOR]

Herein, we report the enantioselective synthesis of a functionalized aza-octahydropentalene and its elaboration to a model tetracyclic core structure of calyciphylline B-type alkaloids. [ABSTRACT FROM AUTHOR]

The hydrogenation of allyl cyanide (but-1-ene-4-nitrile, AC), trans- and cis-crotononitrile (E- and Z-but-2-ene nitrile, TCN and CCN), and methacrylonitrile (2-cyano-1-propene, MCN) were studied, both singly and competitively, over a Pt/alumina catalyst in the liquid phase. Each unsaturated nitrile only underwent C=C bond hydrogenation: no evidence was found for the formation of the saturated or unsaturated amine. The nonconjugated allyl cyanide was found to be the most reactive unsaturated nitrile. Activation energies for the hydrogenation of the C=C bond in AC and MCN were determined giving values of 64 ± 7 kJ mol-1 for AC and 37 ± 4 kJ mol-1 for MCN. The reaction was zero order for both nitriles. Competitive hydrogenations revealed that not only does allyl cyanide react preferentially over the other isomers but also it inhibits the hydrogenation of the other isomers. When all four nitriles were simultaneously hydrogenated, inhibition effects were easily seen suggesting that in terms of strength of bonding to the surface an order of AC > CCN > TCN ∼ MN can be generated. [ABSTRACT FROM AUTHOR]

High explosives that are photoactive, i.e., can be initiated with light, offer significant advantages in reduced potential for accidental electrical initiation. We examined a series of structurally related tetrazine based photoactive high explosive materials to detail their photochemical and photophysical properties. Using photobleaching infrared absorption, we determined quantum yields of photochemistry for nanosecond pulsed excitation at 355 and 532 nm. Changes in mass spectrometry during laser irradiation in vacuum measured the evolution of gaseous products. Fluorescence spectra, quantum yields, and lifetimes were measured to observe radiative channels of energy decay that compete with photochemistry. For the 6 materials studied, quantum yields of photochemistry ranged from <10-5 to 0.03 and quantum yield of fluorescence ranged from <10-3 to 0.33. In all cases, the photoexcitation nonradiatively relaxed primarily to heat, appropriate for supporting photothermal initiation processes. The photochemistry observed was dominated by ring scission of the tetrazine, but there was evidence of more extensive multistep reactions as well. [ABSTRACT FROM AUTHOR]

In the presence of CuI, 1,3-dipolar cycloadditions of N,N'-cyclic azomethine imines with iminooxindoles proceeded readily and furnished novel oxindole spiro-N,N-bicyclic heterocycles in moderate to excellent chemical yields with excellent diastereoselectivities. [ABSTRACT FROM AUTHOR]

A unifiedstrategy for the synthesis of the cis-phlegmarinegroup of alkaloids is presented, leading to the firstsynthesis of serratezomine E (1) as well as the putativestructure of huperzine N (2). A contrasteric hydrogenationmethod was developed based on the use of Wilkinson’s catalyst,which allowed the facial selectivity of standard hydrogenation tobe completely overturned. Calculations were performed to determinethe mechanism, and structures for huperzines M and N are reassigned. [ABSTRACT FROM AUTHOR]

Catalytic aerobic oxidation of phenyl hydroxycarbamate 1 and 1-hydroxy-3-phenylurea 2 using CuCl2 and 2-ethyl-2-oxazoline in methanol gave acyl nitroso species in situ, which were trapped in nitroso-Diels–Alder (NDA) reactions with various dienes to afford the corresponding cycloadducts in high yields (90–98%). Competing ene products were also present for dienes containing both alkene π-bonds and allylic σ-bonds, and the ene yields are higher with 1 than with 2. The use of the chiral hydroxamic acid, (R)-1-hydroxy-3-(1-phenylethylurea) 3 (same conditions) gave NDA cycloadducts in high yields (97–99%) with no ene product from 2,3-dimethyl-1,3-butadiene. NDA cycloadducts were not obtained from other hydroxamic acid analogues [RCONHOH (R = PhCH24; Ph(CH2)25; Ph(CH2)36; Ph(CH2)47; Ph 8; 2-pyridyl 9; 3-pyridyl 10] with various dienes using copper-oxidation but rather were obtained using sodium periodate, resulting in variable NDA yields (13–51%) from hydroxamic acids 1–10 with cyclohexa-1,3-diene and 2,3-dimethyl-1,3-butadiene (several cycloadducts characterized by X-ray crystallography). The NDA and nitroso-ene reaction pathways of nitroso intermediates with dienes were mapped by DFT computations (B3LYP/6-31G*), which showed that the acyl nitroso species are super-reactive and that activation energies in the NDA processes are lower than the isomerization barriers between some cis- and trans-butadienes. [ABSTRACT FROM AUTHOR]

A direct N-trifluoromethylation method has been developed by the use of the in situ generated [ArICF3]+ species as the electrophilic trifluoromethyl source. Upon treatment of N-H ketimines with Ruppert-Prakash reagent in the presence of PhI(OAc)2 and KF, or with Togni's reagent II catalyzed by copper salt, N-trifluoromethylated imine products were obtained in moderate to good yields. [ABSTRACT FROM AUTHOR]

A highly efficient enantioselective hydrogenation of α,β-unsaturated nitriles catalyzed by Rh-(R,R)-f-spiroPhos complex has been developed. With Rh-(R,R)-f-spiroPhos catalyst and under mild conditions, a wide range of α,β-unsaturated nitriles including the (E)- and (Z)-isomers of 3-alkyl-3-aryl, 3,3-diaryl, and 3,3-dialkyl α,β-unsaturated nitriles were hydrogenated to the corresponding chiral nitriles with excellent enantioselectivities (up to 99.9% ee) and high turnover numbers (TON up to 10,000). [ABSTRACT FROM AUTHOR]

Post-assembly modification (PAM) is a powerful tool for the modular functionalization of self-assembled structures. We report a new family of tetrazine-edged FeII4L6 tetrahedral cages, prepared using different aniline subcomponents, which undergo rapid and efficient PAM by inverse electron-demand Diels-Alder (IEDDA) reactions. Remarkably, the electron-donating or -withdrawing ability of the para-substituent on the aniline moiety influences the IEDDA reactivity of the tetrazine ring 11 bonds away. This effect manifests as a linear free energy relationship, quantified using the Hammett equation, between σpara and the rate of the IEDDA reaction. The rate of PAM can thus be adjusted by varying the aniline subcomponent. [ABSTRACT FROM AUTHOR]

A cocatalytic effect of nitro compounds is described for the B(C6F5)3·H2O catalyzed azidation of tertiary aliphatic alcohols, enabling catalyst turnover for the first time and with a broad range of substrates. Kinetic investigations into this surprising effect reveal that nitro compounds induce a switch from first order concentration dependence in Brønsted acid to second order concentration dependence in Brønsted acid and second order dependence in the nitro compounds. Kinetic, electronic, and spectroscopic evidence suggests that higher order hydrogen-bonded aggregates of nitro compounds and acids are the kinetically competent Brønsted acid catalysts. Specific weak H-bond accepting additives may offer a new general approach to accelerating Brønsted acid catalysis in solution. [ABSTRACT FROM AUTHOR]

A synthesis of cardiopetaline has been accomplished via a Wagner-Meerwein rearrangement of a diol having the denudatine skeleton. The Wagner-Meerwein rearrangement could be facilitated simply by heating the diol with p-toluenesulfonic acid in pivalic acid, without preactivating the pivotal hydroxy group. This strategy does not require differentiation of several hydroxy groups in the substrate for the Wagner-Meerwein rearrangement and could be applied to the synthesis of more highly oxygenated aconitine-type diterpenoid alkaloids. [ABSTRACT FROM AUTHOR]

The first regioselective synthesis of polysubstituted 1,2-oxazetidines, based on the [2 + 1 + 1] radical tandem cycloaddition of styrenes, arylamines, and tert-butyl hydroperoxide (TBHP), is described. This simple and direct method allows the synthesis of 1,2-oxazetidines with a broad substrate scope from easily accessible materials. TBHP was employed in this conversion not only as the oxidant but also as the source of "O" for the carbonyl group in the products. [ABSTRACT FROM AUTHOR]

Silylative reduction of nitriles was studied under transition metal-free conditions by using B(C6F5)3 as a catalyst with hydrosilanes as a reductant. Alkyl and (hetero)aryl nitriles were efficiently converted to primary amines or imines under mild conditions. The choice of silanes was found to determine the selectivity: while a full reduction of nitriles was highly facile, the use of sterically bulky silanes allowed for the partial reduction leading to N-silylimines. [ABSTRACT FROM AUTHOR]

Imine-linked covalent organic frameworks (COFs) were synthesized to bear content-tunable, accessible, and reactive ethynyl groups on the walls of one-dimensional pores. These COFs offer an ideal platform for pore-wall surface engineering aimed at anchoring diverse functional groups ranging from hydrophobic to hydrophilic units and from basic to acidic moieties with controllable loading contents. This approach enables the development of various tailor-made COFs with systematically tuned porosities and functionalities while retaining the crystallinity. We demonstrate that this strategy can be used to efficiently screen for suitable pore structures for use as CO2 adsorbents. The poresurface- engineered walls exhibit an enhanced affinity for CO2, resulting in COFs that can capture and separate CO2 with high performance. [ABSTRACT FROM AUTHOR]

An unprecedented asymmetric catalytic tandem aminolysis/aza-Michael addition reaction of spirocyclic para-dienoneimides has been designed and developed through organocatalytic enantioselective desymmetrization. A unified strategy based on this key tandem methodology has been divergently explored for the asymmetric total synthesis of two natural Apocynaceae alkaloids, (+)-deethylibophyllidine and (+)-limaspermidine. The present studies not only enrich the tandem reaction design concerning the asymmetric catalytic assembly of a chiral all-carbon quaternary stereocenter contained in the densely functionalized hydrocarbazole synthons but also manifest the potential for the application of the asymmetric catalysis based on the para-dienone chemistry in asymmetric synthesis of natural products. [ABSTRACT FROM AUTHOR]

Bulky triazenides were utilized in the reaction with pnictogen(III) chlorides (ECl3, E = P, As, Sb, and Bi) yielding triaza-pnicta-butene analogues of the type R-N=N-N(R)-ECl2 (R = Ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl). Subsequent reduction of these dichloro-species afforded unprecedented four-membered group 15 heterocycles [E(μ-NTer)2N] bearing one dicoordinate pnictogen and nitrogen atom. These N3E rings represent species at the borderline between singlet biradicaloids and zwitterions with diminished reactivity compared to known singlet biradicaloids. The N3P compound could be identified, while N3As and N3Sb species as well as the precursor compounds were fully characterized. [ABSTRACT FROM AUTHOR]

S-Nitroso compounds have received much attention in biological research. In addition to their role as nitric oxide donors, there is growing evidence that these compounds are involved in signaling processes in biological systems. Determination of S-nitrosylated proteins is of great importance for fundamental biological research and medical applications. The most common method to assay biological S-nitroso compounds is to chemically or photochemically reduce SNO functional groups to release nitric oxide, which is then entrained in an inert gas stream and detected, usually through chemiluminescence. We report a method of S-nitroso compound detection using cavity ring-down measurements of gaseous NO absorbance at 5.2 μm. The proposed method, in contrast to the chemiluminescence-based approach, can be used to distinguish isotopic forms of NO. We demonstrated sensitivity down to ˜2 pmol of S14NO groups and ˜5 pmol of S15NO groups for S-nitroso compounds in aqueous solutions. The wide dynamic range of cavity ring-down detection allows the measurement of S-nitroso compound levels from pico- to nanomole amounts. [ABSTRACT FROM AUTHOR]

Positive matrix factorization (PMF) has been applied to single particle ATOFMS spectra collected on a six lane heavily trafficked road in central London (Marylebone Road), which well represents an urban street canyon. PMF analysis successfully extracted 11 factors from mass spectra of about 700 000 particles as a complement to information on particle types (from K-means cluster analysis). The factors were associated with specific sources and represent the contribution of different traffic related components (i.e., lubricating oils, fresh elemental carbon, organonitrogen and aromatic compounds), secondary aerosol locally produced (i.e., nitrate, oxidized organic aerosol and oxidized organonitrogen compounds), urban background together with regional transport (aged elemental carbon and ammonium) and fresh sea spray. An important result from this study is the evidence that rapid chemical processes occur in the street canyon with production of secondary particles from road traffic emissions. These locally generated particles, together with aging processes, dramatically affected aerosol composition producing internally mixed particles. These processes may become important with stagnant air conditions and in countries where gasoline vehicles are predominant and need to be considered when quantifying the impact of traffic emissions. [ABSTRACT FROM AUTHOR]

Highly diastereoselective and enantioselective reactions between 2-aroylvinylcinnamaldehydes and α,β-unsaturated imines were achieved under asymmetric catalysis of chiral triazole carbene catalysts. In the presence of N-anisylindeno[2,1-b]triazolo[4,3-d][1,4]oxazinium salt, the reaction of 2-aroylvinylcinnamaldehydes with α,β-unsaturated imines afforded indeno[2,1-c]pyran-1-one derivatives 4 with 90%-99% ee, while enantiopure indenocyclopentan-1-ones 5 (>99% ee) were obtained under the catalysis of N-mesitylindeno[2,1-b]triazolo[4,3-d][1,4]oxazinium salt. A slight variation of an N-substituent on triazole carbenes was found to switch completely the diastereoselectivity of the reaction for the formation of indeno[2,1-c]pyran-1-ones. [ABSTRACT FROM AUTHOR]

Subporphyrinato boron(III) hydrides were prepared by reduction of subporphyrinato boron(III) methoxides with diisobutylaluminum hydride (DIBAL-H) in good yields. The authenticity of the B -H bond has been unambiguously confirmed by a ¹H NMR signal that appears as a broad quartet at -2.27 ppm with a large coupling constant with the central 11UB, characteristic B-H infrared stretching frequencies, and single crystal X-ray diffraction analysis. Red shifts in the corresponding absorption and fluorescence profiles are accounted for in terms of the electron-donating nature of the B-hydride. The hydridic character of subporphyrinato boron(III) hydrides has been demonstrated by the production of H2 via reaction with water or HCl, and controlled reductions of aromatic aldehydes and imines in the presence of a catalytic amount of Ph3C[B(C6F5)4], [ABSTRACT FROM AUTHOR]

A strategy has been developed that culminated in a stereoselective total synthesis of the tetracyclic antimalarial Myrioneuron alkaloid myrioneurinol. The synthesis relies on three highly diastereoselective reactions, including an intramolecular chelation-controlled Michael spirocyclization of an N-Cbz-lactam titanium enolate to an α,β-unsaturated ester for construction of the A/D-ring system and the attendant C5 (quaternary), C6 relative stereochemistry; a malonate enolate conjugate addition to a nitrosoalkene in order to install the appropriate functionality and establish the configuration at C7; and an intramolecular aza-Sakurai reaction to form the B-ring and the accompanying C9 and C10 stereocenters. [ABSTRACT FROM AUTHOR]

A mild and efficient one-pot procedure is described to transform salicylaldoximes into salicylonitriles using Mitsunobu chemistry. The reactions proceed through the corresponding 1,2-benzisoxazoles that undergo the Kemp elimination in situ to generate the target salicylonitriles in excellent yields. The chemistry exhibits a broad scope, and the salicylonitriles can be readily isolated by a simple acid-base workup. In addition to functioning as useful synthetic precursors, salicylonitriles may serve as more cell penetrable bioisosteres of carboxylic acids. [ABSTRACT FROM AUTHOR]

The asymmetric total synthesis of (-)-14,15-dihydrosecurinine and the formal total synthesis of (-)-securinine were accomplished starting from an easily available malimide. A concise SmI2-mediated radical coupling strategy has been developed to construct the bridged α-hydroxy 6-azabicyclo[3.2.1]octanone in four steps with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

In the present work, the combinedelectronic structure calculationsand dynamics simulations have been performed to explore the decompositionreactions of 2H-azirine, 2-phenyl-2H-azirine, and 3-phenyl-2H-azirine in gas phase.Thermal cleavage of the C–C single bond yields nitrile ylidesas products with a high barrier (>50.0 kcal mol–1). On the other hand, photochemical cleavage reactions starting fromthe 1nπ* state of 2H-azirine and3-phenyl-2H-azirine are ultrafast nonadiabatic processes(<100 fs), leading to nitrile ylides through the S1/S0conical intersection. The fast formation of ylides in experimentswas well reproduced by present dynamics simulations. For 3-phenyl-2H-azirine, population of the S1(1ππ*)state is another decay pathway for the S2(1nπ*)state. The C–N bond cleavage upon photoexcitation was usuallyconsidered to take place in T1state. However, our calculationsreveal that photocleavage of the C–N single bond for 2-phenyl-2H-azirine is very likely to take place in S1state.The present work provides new insights into photocleavage mechanismof 2H-azirine and the related derivatives. [ABSTRACT FROM AUTHOR]