Experimental analysis towards vehicular Ad-hoc networks

Presentamos en este trabajo resultados de medición y análisis realizado sobre importantes características de modelos de propagación inalámbrica en Redes Ad-hoc Vehiculares (RAV) en autopistas: Efecto Doppler, propagación de las señales en espacio libre, pérdidas por trayectoria y el margen de operación del sistema. En este trabajo hemos considerado tarjetas inalámbricas 802.11b para la comunicación intervehicular. En el análisis analítico, se han usado dos modelos de propagación: modelos a pequeña y gran escala. Por un lado, de acuerdo a los modelos de gran escala, la máxima distancia entre el transmisor y el receptor es de 446 m., con un margen de operación del sistema (MOS) de 13 dB, el cual está sobre el mínimo margen recomendado. Por el otro lado, se ha encontrado con el resultado de modelos a pequeña escala, que el efecto Doppler no afecta la comunicación entre transmisor y receptor en altas velocidades. Finalmente, se ha realizado un experimento que permite validar los resultados obtenidos analíticamente en el escenario más adverso posible, que es cuando el transmisor y receptor viajan en direcciones opuestas. Con los resultados experimentales se ha concluido que es posible enviar un mínimo de 8 mensajes cuando las antenas del transmisor y receptor se montan al interior de los automóviles

Directed Markovnikov Hydroarylation and Hydroalkenylation of Alkenes Under Nickel Catalysis

We report a full account of our research on nickel-catalyzed Markovnikov-selective hydroarylation and hydroalkenylation of non-conjugated alkenes, which has yielded a toolkit of methods that proceed under mild conditions with alkenyl sulfonamide, ketone, and amide substrates. Regioselectivity is controlled through catalyst coordination to the native Lewis basic functional groups contained within these substrates. To maximize product yield, reaction conditions were fine-tuned for each substrate class, reflecting the different coordination properties of the directing functionality. Detailed kinetic and computational studies shed light on the mechanism of this family of transformations, pointing to transmetalation as the turnover-limiting step

Sulfonamide Directivity Enables Ni-Catalyzed 1,2-Diarylation of Diverse Alkenyl Amines

1,2-Diarylation of alkenyl sulfonamides with aryl iodides and aryl boronic esters under nickel catalysis is reported. The developed method tolerates coupling partners with disparate electronic properties and substitution patterns. 1,2- and 1,1-Disubstituted alkenes, as well as alkenes distal from the directing group, are all accommodated. Control experiments are consistent with a N–Ni coordination mode of the directing group, which stands in contrast to earlier reports on amide-directed 1,2-diarylation that involve carbonyl coordination. The synthetic utility of the method arises from the dual function of the sulfonamide as both a directing group and masked amine nucleophile. This is highlighted by various product diversifications where complex amine compounds are synthesized in a two-step sequence of N-functionalization and deprotection of the sulfonyl group

Catalytic, Enantioselective α-Alkylation of Azlactones with Non-Conjugated Alkenes via Directed Nucleopalladation

A palladium(II)-catalyzed enantioselective α-alkylation of azlactones with non-conjugated alkenes is described. The reaction employs a chiral BINOL-derived phosphoric acid as the source of stereoinduction and a cleavable bidentate directing group appended to the alkene to control regioselectivity and stabilize the nucleopalladated alkylpalladium(II) intermediate in the catalytic cycle. A wide range of azlactones were found to be compatible under the optimal conditions to afford products bearing α,α-disubstituted α-amino acid derivatives with high yields and high enantioselectivity

Nickel-Catalyzed 1,2-Diarylation of Alkenyl Ketones: A Comparative Study of Carbonyl-Directed Reaction Systems

A conjunctive cross-coupling reaction of alkenyl ketones, aryl iodides, and arylboronic esters under nickel catalysis is reported. The reaction delivers the desired 1,2-diarylated products with moderate to excellent regiocontrol using a diverse array of ketone starting materials, as illustrated across over 40 examples. To showcase the versatility of this method, a representative product is diversified into a wide range of synthetically useful building blocks, that are not readily accessible via existing 1,2-diarylation reactions. Preliminary mechanistic studies shed light on the binding mode of the substrate, and Hammett analysis shows the effect of electronic factors on initial rates. To our knowledge, this method represents the first example of catalytic 1,2-diarylation of an alkene, directed by a native ketone functional group.</div

An Under-Appreciated Source of Reproducibility Issues in Cross-Coupling: Solid-State Decomposition of Primary Sodium Alkoxides in Air

The decomposition of primary sodium alkoxide salts under ambient storage conditions and the effects of this phenomenon on commonly employed transition-metal-catalyzed cross-coupling reactions are described. By utilizing NMR, IR, and Raman spectroscopy, along with a modified Karl Fischer analysis, the main inorganic degradants were characterized, and CO2 in the air was found to be a critical reactant within the decomposition process. The effects of storage conditions on decomposition were evaluated, and the preliminary experiments to understand the kinetics of this process were performed

Atom-Economical Cross-Coupling of Internal and Terminal Alkynes to Access 1,3-Enynes

Selective carbon–carbon (C–C) bond formation in chemical synthesis generally requires pre-functionalized building blocks. However, the requisite pre-functionalization steps undermine the efficiency of multi-step synthetic sequences, which is particularly problematic in large-scale applications, such as in the commercial production of pharmaceuticals. Herein, we describe a selective and catalytic method for synthesizing 1,3-enynes without pre-functionalized building blocks. This method is facilitated by a tailored P,N-ligand that enables regioselective coupling and suppresses secondary E/Z-isomerization of the product. The transformation enables several classes of unactivated internal acceptor alkynes to be coupled with terminal donor alkynes to deliver 1,3-enynes in a highly regio- and stereoselective manner. The scope of compatible acceptor alkynes includes propargyl alcohols, (homo)propargyl amine derivatives, and (homo)propargyl carboxamides. The reaction is scalable and can operate effectively with 0.5 mol% catalyst loading. The products are versatile intermediates that can participate in various downstream transformations. We also present preliminary mechanistic experiments that are consistent with a redox-neutral Pd(II) catalytic cycle

Three-Component Asymmetric Ni-Catalyzed 1,2-Dicarbofunctionalization of Unactivated Alkenes via Stereoselective Migratory Insertion

An asymmetric 1,2-dicarbofunctionalization of unactivated alkenes with aryl iodides and aryl/alkenylboronic esters under nickel/bioxazoline catalysis is disclosed. A wide array of aryl and alkenyl nucleophiles are tolerated, furnishing the products in good yield and with high enantioselectivity. In addition to terminal alkenes, 1,2-disubstituted internal alkenes participate in the reaction, establishing two contiguous stereocenters with high diastereoselectivity and moderate enantioselectivity. A combination of experimental and computational techniques shed light on the mechanism of the catalytic transformation, pointing to a closed-shell pathway with an enantiodetermining migratory insertion step, where stereoinduction arises from synergistic interactions between the sterically bulky achiral sulfonamide directing group and the hemilabile bidentate ligand