Pd-Catalyzed Cross-Coupling Reactions of Hydrazones: Regioselective Synthesis of Highly Branched Dienes

The regioselective formation of highly branched dienes is a challenging task. Design and exploration of alternative working models to achieve such a regioselectivity to accomplish highly branched dienes is considered to be a historical advancement of Heck reaction to construct branched dienes. On the basis of the utility of carbene transfer reactions, in the reaction of hydrazones with Pd(II) under oxidative conditions, we envisioned obtaining a Pd-bis-carbene complex with alpha-hydrogens, which can lead to branched dienes. Herein, we report a novel Pd-catalyzed selective coupling reaction of hydrazones in the presence of t-BuOLi and benzoquinone to form the corresponding branched dienes. The utility of the Pd catalyst for the cross-coupling reactions for synthesizing branched conjugated dienes is rare. The reaction is very versatile and compatible with a variety of functional groups and is useful in synthesizing heterocyclic molecules. We anticipate that this Pd-catalyzed cross-coupling reaction will open new avenues for synthesizing useful compounds.

Insertion Reactions of Six-Membered Cyclopalladated N,N `,N `'-Triarylguanidine, Pd{kappa(2)(C,N)-C6H3Me-3(NHC(NHAr)(=NAr))-2)(mu-Br)](2) (Ar=2-MeC6H4) with PhCC C-C(O)OR (R = Me and Et): A Gateway to Second Orthopalladation through Novel Rearrangements

The reaction of Pd{kappa(2)(C,N)-C6H3Me-3-(NHC(NHAr)(=NAr))-2}(mu-Br)](2) (Ar = 2-MeC6H4; 1) with 4 equiv of PhC C-C(O)OMe in CH2Cl2 afforded Pd{kappa(2)(C,N)-C(Ph)=C(C(O)OMe)C(Ph)=C(C(O)-OMe)C6H3Me-3(N=C(NH Ar)(2))-2}Br] (Ar = 2-MeC6H4; 2) in 70% yield, and the aforementioned reaction carried out with 10 equiv of PhC C-C(O)OR (R = Me, and Et) afforded an admixture of two regioisomers of Pd{kappa(3)(N,C,O)-O=C(OR)-C5Ph3(C(O)OR)C(C(O)OR)C6H3Me-3(N=C(NHAr)( 2))- 2}Br] (Ar = 2-MeC6H4; R = Me (3a/3b), Et (4a/4b)) in 80 and 87% yields, respectively. In one attempt, the minor regioisomer, 4b, was isolated from the mixture in 6% yield by fractional crystallization. Palladacycles 3a/3b and 4a/4b, upon stirring in CH2Cl2/MeCN (1/1, v/v) mixture at ambient condition for S days, afforded Pd{eta(3)-allyl,(KN)-N-1)-C-5(C(O)OR)(2)Ph3C-(C(O)OR)C6H3Me-3(N=C(NH Ar)(2))(-2)}Br] (Ar = 2-MeC6H4; R = Me (5a/5b), Et (6a/6b)) in 94 and 93% yields, respectively. Palladacycles 3a/3b and 4a/4b, upon reaction with AgOTf in CH2CH2/Me2C(O) (1/1, v/v) mixture at ambient temperature for 15 min, afforded Pd{kappa(3)(N,C,O)-O=C(OR)C5Ph3(C(O)OR)C(C(O)OR)C6H3Me-3(N=C(NHAr)(2 ))-2}(OTf)] (Ar = 2-MeC6H4; R = Me (7a/7b), Et (8a/8b)) in 79 and 77% yields, respectively. Palladacycles 7a/7b and 8a/ 8b, upon reflux in PhC1 separately for 6 h, or palladacycles 5a/5b and 6a/6b, upon treatment with AgOTf in CH2Cl2/Me2C(O) (7/3, v/v) mixture for 15 min, afforded Pd{(eta(2)-Ph)C5Ph2(C(O)OR)kappa(2)(C,N)-C(C(O)OR)C6H3Me-3(N=C(NHAr) (2))-2}(OTf)] (Ar = 2-MeC6H4; R = Me (9a/9h), Et (10a/10b)) in >= 87% yields. Palladacycles 9a/9b, upon stirring in MeCN in the presence of excess NaOAc followed by crystallization of the reaction mixture in the same solvent, afforded Pd{kappa(3)(N,C,C)-(C6H4)C5Ph2(C(O)OMe)(2)C(C(O)OMe)(2)C6H3Me-3(N=C( NHAr)(2))-2}(NCMe)] (Ar = 2-MeC6H4; 11a/11b) in 82% yield. The new palladacycles were characterized by analytical, IR, and NMR (H-1 and C-13) spectroscopic techniques, and the molecular structures of 2, 3a, 4a, 4b, 5a, 6a, 7a, 9a, 10a, and 11a-d(3) were determined by single crystal X-ray diffraction. The frameworks in the aforementioned palladacycles, except that present in 2, are unprecedented. Plausible pathways for the formation of new palladacycles and the influence of the guanidine unit in 1, substituents in alkynes, reaction conditions, and electrophilicity of the bromide and the triflate upon the frameworks of the insertion products have been discussed.

Enantioselective synthesis of macrolactone core of the natural product Sch725674

An enantioselective synthesis of the macrolactone core of natural product Sch725674 was accomplished from furfural. Key reactions in assembly of the macrolactone are the use of furan as a but-2-ene-dione equivalent and ring closing metathesis. (C) 2014 Elsevier Ltd. All rights reserved.

Beyond the ``Coffee Ring'': Re-entrant Ordering in an Evaporation-Driven Self-Assembly in a Colloidal Suspension on a Substrate

We study the phenomenon of evaporation-driven self-assembly of a colloid suspension of silica microspheres in the interior region and away from the rim of the droplet on a glass plate. In view of the importance of achieving a large-area, monolayer assembly, we first realize a suitable choice of experimental conditions, minimizing the influence of many other competing phenomena that usually complicate the understanding of fundamental concepts of such self-assembly processes in the interior region of a drying droplet. Under these simplifying conditions to bring out essential aspects, our experiments unveil an interesting competition between ordering and compaction in such drying systems in analogy to an impending glass transition. We establish a re-entrant behavior in the order disorder phase diagram as a function of the particle density, such that there is an optimal range of the particle density to realize the long-range ordering. The results are explained with the help of simulations and phenomenological theory.

Synergistic electrochemical activity of titanium carbide and carbon towards fuel cell reactions

Titanium carbide (TiC) is an electrically conducting refractory interstitial compound possessing several unique properties. A cost-effective, efficient and non-Pt electrocatalyst based on TiC is explored and the multi-functionality of TiC towards various electrochemical reactions that are of significant interest in low temperature fuel cells is studied. Ameliorated activities towards oxygen reduction reaction (ORR) and borohydride oxidation are observed with TiC-carbon composites. High sensitivity and selectivity towards ORR have been demonstrated with very good methanol tolerance. The charge transfer interactions between TiC and carbon seem to play a vital role in the improved activity as compared to their individual counterparts. The present study opens up a way to realize completely Pt-free borohydride fuel cell architecture.

Novel synthesis of carbohydrate fused alpha-amino gamma-lactams and glycopeptides by NIS mediated ring opening of donor-acceptor substituted cyclopropanes

alpha-Amino gamma-lactams have been synthesized from carbohydrate derived cyclopropanecarboxylates using N-iodosuccinimide (NIS) and NaN3. Cyclopropane ring opening with NIS and NaN3 in different solvents has been studied. Reductive cyclization of the intermediate di-azides leads to the carbohydrate fused alpha-amino gamma-lactam and gamma-lactams. Additionally, the methodology has been successfully extended to the synthesis of a glycopeptide. (C) 2014 Elsevier Ltd. All rights reserved.

Activation of Fly Ash–Lime Reactions: Kinetic Approach

Lime–fly ash reactions play a key role in improving the mechanical strength and tailoring the permeability characteristics of compacted fly ash. Activation of fly ash–lime pozzolanic reactions should accelerate the rate of strength development and possibly mobilize higher compressive strengths, facilitating improved engineering performance of fly ash amended materials. This paper makes an assessment of activation of lime–fly ash reactions by curing compacted fly ash–lime specimens at ambient (25°C) and at elevated temperature (80°C). The kinetics of fly ash–lime reactions are examined by monitoring the reacted lime as a function of curing period and temperature. The influence of variations in fly ash/lime content and dry density on the compressive strength developed by specimens at both temperatures is evaluated. The thermodynamic parameters for the fly ash–lime reactions have also been examined. Experimental results showed that curing at 80°C for 24 h accelerated fly ash–lime reactions such that it caused the steam cured (SC) specimens to evelop 1.21–2.44 fold larger strengths than room-temperature cured (RTC) specimens cured at 25°C for 28 days. Analysis of thermodynamic parameters indicated that the fly ash–lime reactions are thermodynamically favored at fly ash contents of 50–70% and lime additions of 16–20%, and the reactions are endothermic in nature. DOI: 10.1061/(ASCE)MT.1943-5533.0000482. © 2012 American Society of Civil Engineers.

A Contraction Mapping Approach for Robust Estimation of Lagged Autocorrelation

We consider the zero-crossing rate (ZCR) of a Gaussian process and establish a property relating the lagged ZCR (LZCR) to the corresponding normalized autocorrelation function. This is a generalization of Kedem's result for the lag-one case. For the specific case of a sinusoid in white Gaussian noise, we use the higher-order property between lagged ZCR and higher-lag autocorrelation to develop an iterative higher-order autoregressive filtering scheme, which stabilizes the ZCR and consequently provide robust estimates of the lagged autocorrelation. Simulation results show that the autocorrelation estimates converge in about 20 to 40 iterations even for low signal-to-noise ratio.

Estimation of the 2.0(5) helix type i -> i hydrogen bond energy at Aib*-Oxa motif: an isodesmic approach

Bending at the valence angle N-C-alpha-C' (tau) is a known control feature for attenuating the stability of the rare intramolecular hydrogen bonded pseudo five-membered ring C-5 structures, the so called 2.0(5) helices, at Aib. The competitive 3(10)-helical structures still predominate over the C5 structures at Aib for most values of tau. However at Aib*, a mimic of Aib where the carbonyl 0 of Aib is replaced with an imidate N (in 5,6-dihydro-4H-1,3-oxazine = Oxa), in the peptidomimic Piv-Pro-Aib*-Oxa (1), the C(5)i structure is persistent in both crystals and in solution. Here we show that the i -> i hydrogen bond energy is a more determinant control for the relative stability of the C5 structure and estimate its value to be 18.5 +/- 0.7 kJ/mol at Aib* in 1, through the computational isodesmic reaction approach, using two independent sets of theoretical isodesmic reactions. (C) 2014 Elsevier Ltd. All rights reserved.

An inhomogeneous multispecies TASEP on a ring

We reinterpret and generalize conjectures of Lam and Williams as statements about the stationary distribution of a multispecies exclusion process on the ring. The central objects in our study are the multiline queues of Ferrari and Martin. We make some progress on some of the conjectures in different directions. First, we prove Lam and Williams' conjectures in two special cases by generalizing the rates of the Ferrari-Martin transitions. Secondly, we define a new process on multiline queues, which have a certain minimality property. This gives another proof for one of the special cases; namely arbitrary jump rates for three species. (C) 2014 Elsevier Inc. All rights reserved.

Enantiospecific Total Synthesis of Macrolactone Sch 725674

The enantiospecific total synthesis of 14-membered macrolactone Sch 725674 was accomplished from tartaric acid. Key reactions in the synthesis include the Ley's dithiaketalization of an alkynone derived from the bis-Weinreb amide of tartaric acid, Boord olefination, and ring-closing metathesis of an acrylate ester.

Molecular topology of three ring nematogens from C-13-H-1 dipolar couplings

Molecules in their liquid crystalline phase undergo rotational motion about the long axis of the molecule and the shape adopted by the rotating molecule plays an important role in influencing the mesophase morphology. In this context, obtaining the topology and the relative orientation of the different sub-units are important steps. For studying the liquid crystalline phase, C-13 NMR spectroscopy is a convenient method and for certain specifically designed nematogens, 2-dimensional separated local field (2D-SLF) NMR spectroscopy provides a particularly simple and straightforward means of arriving at the molecular topology. We demonstrate this approach on two three ring based nematogens designed with a phenyl or a thiophene ring at one of the termini. From the C-13-H-1 dipolar couplings of the terminal carbon obtained using the 2D-SLF NMR technique, the order parameter of the local symmetry axis of the terminal phenyl ring as well as of the long molecular axis could be easily estimated. For the thiophene nematogen, the lack of symmetry of the thiophene moiety necessitates some additional computational steps. The results indicate that the thiophene unit has its local ordering axis oriented away from the long molecular axis by a small angle, consistent with a bent structure expected in view of the thiophene geometry. The experiment also demonstrates the ability of 2D-SLF NMR to provide high resolution spectra by separation of several overlapped resonances in terms of their C-13-H-1 dipolar couplings. The results are consistent with a rod-like topology of the core of the investigated mesogens. The investigation demonstrates the potential of 2D-SLF NMR C-13 spectroscopy for obtaining atomistic level information and its utility for topological studies of different mesogens.

Formation of annular austenitic ring between outer ferrite layer and solid globule in a semi-solid processed SS 304L

The microstructure of an austenitic SS 304L rapidly quenched from its semi-solid state shows a unique annular austenitic ring in between the core of each globule and its ferritic outer layer. On the basis of experimental results and microstructural analysis, it is proposed that the ring is formed as a result of preferential austenitic phase nucleation in a small quantity of liquid entrapped between adjacent solid globules during rapid quenching, in spite of the fact that ferrite is the thermodynamically stable phase for the alloy. (C) 2014 Elsevier B.V. All rights reserved.

Depalladation of Neutral Monoalkyne- and Dialkyne-Inserted Palladacycles and Alkyne Insertion/Depalladation Reactions of Cationic Palladacycles Derived from N,N `,N `'-Triarylguanidines as Facile Routes for Guanidine-Containing Heterocycles/Carbocycles: Synthetic, Structural, and Mechanistic Aspects

Depalladation of the monoalkyne-inserted cyclopalldated guanidines (kappa 2(C,N)Pd(2,6-Me2C5H3N)Br] (I and II) in PhCl under reflux conditions and that of the dialkyne-inserted cyclopalladated guanidine kappa(2)(C,N):eta(2)(C=C)PdBr] (III) in pyridine under reflux conditions afforded a guanidine-containing indole (1), imidaziondole (2), and benzazepine (3) in 80%, 67%, and 76%, yields, respectively. trans-L2PdBr2] species (L = 2,6-Me2C5H3N, C5H5N) were also isolated in the aforementioned reactions in 35%, 42%, and 40% yields. Further , the reaction of the cyclopalladated guanidine kappa(2)(C,N)Pd(mu-Br)](2) (IV) with AgBF4 in a CH2Cl2/MeCN mixture afforded the cationic pincer type cyclopalladated guanidine kappa(3)(C,N,O)Pd(MeCN)]BF4] (4) in 85% yield and this palladacycle upon crystallization in MeCN and the reaction of kappa(2)(C,N)Pd(mu-Br)](2) (V) with AgBf(4) in a CH2Cl2/MeCN mixture afforded the cationic palladacycles {kappa(2)(C,N)Pd(MeCN)(2)]BF4](5 and 6) in 89% and 91% yields, respectively. The separate reactions of 4 with 2 equiv of methyl phenylpropiolate (MPP) or diphenylacetylene (DPA) and the reaction of 5 with 2 equiv of MPP in PhCl at 110 degrees C afforded the guanidine-containing quinazolinium tetrafluoroborate 7 in 25-32% yields. The reaction of 6 with 2 equiv of DPA under otherwise identical conditions afforded the unsymmetrically substituted guanidinium tetrafluoroborate 8, containing a highly substituted naphthalene unit, in 82% yield. Compounds 1-8 were characterized by analytical and spectroscopic techniques, and all compounds except 4 were characterized by single-crystal X-ray diffraction. The Molecular structure of 2 and 3 are nove, as the framework in the former arises due to the formation of two C-N bonds upon depalladation while the butadienyl unit in the latter revealed cis,cis stereochemistry, a-feature unprecedented in alkyne insertion chemistry. Plausible pathways for the formation of heterocycles/carbocycles are proposed. the influence of substitutents on the aryl rings fo the cyclopalladated guanidine moiety and those on alkynes upon the nature of the products in addressed. Heterocycles 1 and 7 revealed the presence of two rotamers in about a 1.00:0.43 ratio in CDCl3 and in about a 1.00:0.14 ratio in CD3OD, respectively, as detected by H-1 NMR spectroscopy while in CD3CN and DMSO-d(6) (1) and CD3CN and CDCl3 (7), these heterocycles revealed the presence of a single rotamer. These spectral features are attributed to the restricted C-N single-bond rotation of the CN3 unit of the guanidine moiety, which possibly arises from steric constraint due to the formation of a N-H center dot center dot center dot Cl hydrogen bond with CDCl3 (1) and N-H center dot center dot center dot O and O-D center dot center dot center dot O hydrogen bonds with CD3OD (7).

Exclusive Detection of Sub-Nanomolar Levels of Palladium(II) in Water: An Excellent Probe for Multiple Applications

A new colorimetric probe has been developed for the detection and estimation of Pd-II at sub-nanomolar concentrations. The probe consisted of rhodamine (signaling unit), which was linked with a bis-picolyl moiety (binding site) through a phenyl ring. Pd-II induced opening of the spirolactam ring of the probe with the generation of a prominent pink color. The excellent selectivity of the probe towards Pd-II over Pd-0 or Rh-II ensured its potential utility for the detection of residual palladium contamination in pharma-ceutical drugs and in Pd-catalyzed reactions. The probe showed a ``turn-on'' (bright yellow) fluorescence upon the addition of Pd-II, which made it suitable for the detection of Pd contaminants in mammalian cells.