Reactive Switching Research Articles

Direct Metal-Free Entry to Aminocyclobutenes or Aminocyclobutenols from Ynamides: Synthetic Applications.

The [2+2] cycloaddition of ynamides with the highly polarized reagent Tf2 C=CH2 has been developed to regioselectively afford bis(triflyl)aminocyclobutenes in the absence of catalyst under mild conditions. Incidentally, with the ynamides bearing electron-rich aromatic rings at the C-terminal, an interesting reactivity switch was observed; a cyclization/hydroxylation sequence yielded 2-amino-3-(triflyl)cyclobut-2-enols. Aminocyclobutene construction with addition of alcohols resulted in the formation of aminocyclobutenyl ethers through a cyclization/hydroalkoxylation process. Moreover, the utility of functionalized aminocyclobutenes as precursors for further elaboration was demonstrated with the preparation of α-amino-β,γ-unsaturated ketones and 3-(triflyl)buta-1,3-dien-2-amines through 4 π-electrocyclic ring opening.

ChemInform Abstract: Catalytic Enantioselective Arylative Dearomatization of 3‐Methyl‐2‐vinylindoles Enabled by Reactivity Switch.

AbstractThe first catalytic asymmetric dearomatization of 3‐methyl‐2‐vinylindoles is established by using quinone monoimides as suitable electrophiles in the presence of a chiral phosphoric acid, which affords chiral indole derivatives bearing a quaternary stereogenic center in a chemospecific and highly enantioselective fashion.

Catalysts Encapsulated in Molecular Machines.

Smart catalysts offer the control of chemical processes and sequences of transformations, and catalysts with unique catalytic behavior can afford chiral products or promote successive polymerization. To meet advanced demands, the key to constructing smart catalysts is to incorporate traditional catalytic functional groups with trigger-induced factors. Molecular machines with dynamic properties and particular topological structures have typical stimulus-responsive features. In recent years, scientists have made efforts to utilize molecular machines (molecular switches, rotaxanes, motors, etc.) as scaffolds to develop smart catalysts. This Minireview focuses on the achievements of developing catalysts encapsulated in molecular machines and their remarkable specialties. This strategy is believed to provide more potential applications in switchable reactions, asymmetric synthesis, and processive catalysis.

Controlling reactivity by remote protonation of a basic side group in a bifunctional photoacid.

6-Hydroxy-2-naphthoic acid and its sulfonate derivatives belong to a family of bifunctional photoacids where the -OH group acts as a proton donor and the -COO(-) group acts as a proton acceptor. Upon electronic excitation, the -OH group becomes more acidic and the -COO(-) group turns more basic. Change in the ionization state of one functional group causes a change (switch) in the reactivity of the other functional group. Using picosecond time-resolved and steady state spectroscopy, we find clear evidence for an ultrafast reactivity switch caused by a diffusional proton transfer through the water solvent between the two functional groups with no evidence of a concerted proton transfer.

Inside Back Cover: Catalytic Enantioselective Arylative Dearomatization of 3-Methyl-2-vinylindoles Enabled by Reactivity Switch (Adv. Synth. Catal. 18/2015)

Inside Back Cover: Catalytic Enantioselective Arylative Dearomatization of 3-Methyl-2-vinylindoles Enabled by Reactivity Switch (Adv. Synth. Catal. 18/2015)

Catalytic Enantioselective Arylative Dearomatization of 3‐Methyl‐2‐vinylindoles Enabled by Reactivity Switch

AbstractThe first catalytic asymmetric dearomatization of 3‐methyl‐2‐vinylindoles has been established by using quinone monoimides as suitable electrophiles in the presence of chiral phosphoric acid, which afforded chiral indole derivatives bearing a quaternary stereogenic center in a chemospecific and highly enantioselective fashion (up to 81% yield, >99% ee). The success of this reaction was enabled by the reactivity switch of 3‐methyl‐2‐vinylindoles, which has not been reported before. This reaction also represents the first catalytic asymmetric arylative dearomatization of vinylindoles, which will help confront the challenges in catalytic asymmetric arylative dearomatization and dearomatization of vinylindoles.magnified image

ChemInform Abstract: N‐Heterocyclic Carbene Catalyzed Switchable Reactions of Enals with Azoalkenes: Formal [4 + 3] and [4 + 1] Annulations for the Synthesis of 1,2‐Diazepines and Pyrazoles.

AbstractVarious 1,2‐diazepine derivatives are synthesized by regio‐ and enantioselective formal [4 + 3] annulation reaction between enals and in situ formed azoalkenes.

ChemInform Abstract: Substituent Controlled Reactivity Switch: Selective Synthesis of α‐Diazoalkylphosphonates or Vinylphosphonates via Nucleophilic Substitution of Alkyl Bromides with Bestmann—Ohira Reagent.

AbstractAn efficient method for the selective synthesis of the title compounds (III) and (IV) from commercially available and inexpensive bromides is presented.

Macrophage inflammasome mediates hyperhomocysteinemia-aggravated abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a serious vascular disease with high mortality. Our previous study suggested that hyperhomocysteinemia (HHcy) exaggerates the occurrence of AAA. Here, we investigated whether macrophage inflammasome is involved in HHcy-aggravated AAA formation. Two independent HHcy-aggravated AAA models, perivascular calcium phosphate–treated C57BL/6 mice and angiotensin II (Ang II)–infused apolipoprotein E-deficient (ApoE−/−) mice were used. NLPR3, caspase 1, and interleukin-1β (IL-1β) levels were higher in aneurysmal lesions of both HHcy models compared to controls, preferentially in macrophages. Similarly, macrophage inflammasome activation was observed in vitro. Folic acid administration reversed the HHcy-accelerated AAA, with ameliorated activation of inflammasome in the tunica adventitia. Lentiviral silencing of NLRP3 significantly ameliorated HHcy-aggravated AAA formation. We observed increased mitochondrial production of reactive oxygen species (ROS) and energy switch from oxidative phosphorylation to glycolysis with excess Hcy in macrophages. Blocking mitochondrial ROS production in macrophages abolished inflammasome activation. Our study highlights the potential importance of macrophage inflammasome in the pathogenesis and development of HHcy-aggravated AAA.

LU-MAC: Licensed and Unlicensed MAC Protocol for Cognitive WiFi Network with Jamming-resistant

Abstract Ubiquitous devices used in the day-to-day activities of the modern world, increases the usage of internet via WiFi network. The development of technology and the raise in internet access leads to wireless spectrum scarcity in the ISM band. The deployment of Cognitive radio (CR) in the WiFi network with dynamic channel switching can overcome the spectrum shortage. This integration brings the challenge of jamming in CR network and WiFi network together devastates the availability of the spectrum in Cognitive WiFi (CWF) network. A novel LU-MAC protocol is proposed for CWF network that dynamically operate in both licensed and unlicensed band to increase the spectrum availability with jamming resistant. The LU-MAC protocol have been designed with control frame specification, Data Channel Switching (DCS) process and coordination modules, control channel switching process, synchronization module to obtain the benefit of cognitive radio technology in WiFi network. It is deployed using Intrusion Detection System (IDS), Random Frequency Hopping Pattern (RFHP) generation algorithm and Statistic-based Reactive Channel Switching (SRCS) algorithms to counter the jamming attack. The performance of the LU-MAC protocol is evaluated using the Glomosim simulator. It shows the efficient communication in CWF network with the existence of the jamming attacker.

N-heterocyclic carbene catalyzed switchable reactions of enals with azoalkenes: formal [4 + 3] and [4 + 1] annulations for the synthesis of 1,2-diazepines and pyrazoles.

A regio- and enantioselective formal [4 + 3] annulation reaction between enals and in situ formed azoalkenes has been achieved. A diverse set of 1,2-diazepine derivatives were synthesized in good yields with excellent enantioselectivities (often 99% ee). Alternatively, modifying the standard NHC catalyst switched the reactivity toward a formal [4 + 1] annulation to afford functionalized pyrazoles. The electronic and steric properties of the N-heterocyclic carbene organocatalyst play a vital role in controlling the reaction pathway (homoenolate vs acyl-anion reactivity of enal), allowing selective access to diverse 1,2-diazepine and pyrazole derivatives from identical substrates.

ChemInform Abstract: Remarkable Switch of Regioselectivity in Diels—Alder Reaction: Divergent Total Synthesis of Borreverine, Caulindoles, and Flinderoles.

AbstractA remarkable switch of reactivity of the Diels—Alder dimerization of indole substituted butadienes is discovered.

Individual Differences in Cognitive Strategy During Reactive Task-Set Switching

Researchers who employ traditional laboratory task-set switching paradigms often assume that their participants are using only one strategy to complete switch moves. In the current study, we hypothesized that real world task-set switching behaviors are facilitated by multiple processing strategies, including fast “heuristic” strategies that are employed when switching is routine, and slower “reasoned” strategies that are used less often when heuristic strategies fail. In this study, 151 undergraduate students from George Mason University volunteered to complete the Youmans Cognitive Flexibility Assessment (YCFA), a computer-based, reactive task-set switching paradigm that takes the form of a simple puzzle game. Participants’ reaction time data suggests that they tried to utilize both heuristic and reasoned strategies to make task-set switches, and that they only used reasoned strategies when heuristic strategies failed. The data also revealed that participants quickly abandoned reasoned strategies when heuristic strategies once again become successful. We conclude by providing some guidance for system designers regarding the speed with which humans who are employing reasoned approaches to task-set switching will abandon them once heuristic approaches again become successful, and by discussing the implications of our findings for safe system design.

Ligand Modification Transforms a Catalase Mimic into a Water Oxidation Catalyst

AbstractThe catalytic reactivity of the high‐spin MnII pyridinophane complexes [(Py2NR2)Mn(H2O)2]2+ (R=H, Me, tBu) toward O2 formation is reported. With small macrocycle N‐substituents (R=H, Me), the complexes catalytically disproportionate H2O2 in aqueous solution; with a bulky substituent (R=tBu), this catalytic reaction is shut down, but the complex becomes active for aqueous electrocatalytic H2O oxidation. Control experiments are in support of a homogeneous molecular catalyst and preliminary mechanistic studies suggest that the catalyst is mononuclear. This ligand‐controlled switch in catalytic reactivity has implications for the design of new manganese‐based water oxidation catalysts.

Ligand modification transforms a catalase mimic into a water oxidation catalyst.

The catalytic reactivity of the high-spin Mn(II) pyridinophane complexes [(Py2NR2)Mn(H2O)2](2+) (R=H, Me, tBu) toward O2 formation is reported. With small macrocycle N-substituents (R=H, Me), the complexes catalytically disproportionate H2O2 in aqueous solution; with a bulky substituent (R=tBu), this catalytic reaction is shut down, but the complex becomes active for aqueous electrocatalytic H2O oxidation. Control experiments are in support of a homogeneous molecular catalyst and preliminary mechanistic studies suggest that the catalyst is mononuclear. This ligand-controlled switch in catalytic reactivity has implications for the design of new manganese-based water oxidation catalysts.

ChemInform Abstract: Reactivity Switch Enabled by Counterion: Highly Chemoselective Dimerization and Hydration of Terminal Alkynes.

AbstractThis approach features the combination of a Pd(0) catalyst with a Broensted acid, with a neat tuning of reactivity between dimerization and hydration.

Dynamic simulations of stimuli-responsive switching of azobenzene derivatives in self-assembled monolayers: reactive rotation potential and switching functions

Although the force field (FF)-based molecular dynamics (MD) simulation has been widely applied to rationalise the experimental observations and measurements in chemistry, physics, materials and life science for years, traditional FF suffers from the incapability for describing chemical reactions, which are crucial in many important transformation processes. In order to simulate the collective switching process in azobenzene-based self-assemble monolayers on Au(111) surface, reactive MD simulations with alternative FF were implemented. The classic torsion function has been modified to depict the diabatic potential energy curves for cis and trans isomers, respectively. A switching function is further introduced to connect two N = N rotation functions, and the surface hopping between the cis and trans curves is allowed. By using the reactive rotation potential and switching function, the collective effect of numerous reaction centres and the influence of environment on the quantum yield in the complex system were explored at mesoscopic dimension and timescales. The reactive FF may be also applicable for other complicated systems containing stilbene derivatives. Limitation and perspective for further developments for the other complicated reactions are also addressed.

Development of non-intrusive monitoring for reactive switching of high voltage circuit breaker

High-voltage circuit breakers are among the most important equipments for ensuring the efficient and safe operation of an electric power system. On occasion, circuit breaker operators may wish to check whether equipment is performing satisfactorily and whether controlled switching systems are producing reliable and repeatable stress control. Monitoring of voltage and current waveforms during switching using established methods will provide information about the magnitude and frequency of voltage transients as a result of re-ignitions and restrikes. However, high frequency waveform measurement requires shutdown of circuit breaker and use of specialized equipment. Two utilities, Hydro-Québec in Canada and Powerlink Queensland in Australia, have been working on the development and application of a non-intrusive, cost-effective and flexible diagnostic system for monitoring high-voltage circuit breakers for reactive switching. The proposed diagnostic approach relies on the non-intrusive assessment of key parameters such as operating times, prestrike characteristics, re-ignition and restrike detection. Transient electromagnetic emissions have been identified as a promising means to evaluate the abovementioned parameters non-intrusively.This paper describes two complimentary methods developed concurrently by Powerlink and Hydro-Québec. Also, return of experiences on the application to capacitor bank and shunt reactor switching is presented.

Mechanical Manipulation of Chemical Reactions: Reactivity Switching of Bergman Cyclizations.

Photoswitches incorporated into molecular frameworks have been used since a long time to trigger chemical processes on demand. Here, it is shown how mechanophores can be used as switches in order to drastically change the reactivity of a neighboring functional group as a function of external stress. The reactivities of cyclic enediynes, which are highly toxic agents when undergoing Bergman cyclization, roughly correlate with the distance between the bond-forming carbons in many cases. It is demonstrated how this distance, and thus enediyne reactivity, can be tuned upon applying mechanical stress. Depending on suitable substitution patterns, chemically inert species can be turned into highly reactive ones and vice versa, thus extending the concept of photoswitching to mechanoswitching. Moreover, depending on the derivative, it is found that C1-C5 cyclization becomes energetically preferred over the Bergman (C1-C6) pathway at nano-Newton forces, thus leading to a force-induced switch in selectivity in such cases.

Understanding E2 versus SN2 Competition under Acidic and Basic Conditions

Our purpose is to understand the mechanism through which pH affects the competition between base-induced elimination and substitution. To this end, we have quantum chemically investigated the competition between elimination and substitution pathways in H2O+C2H5OH2+ and OH−+C2H5OH, that is, two related model systems that represent, in a generic manner, the same reaction under acidic and basic conditions, respectively. We find that substitution is favored in the acidic case while elimination prevails under basic conditions. Activation-strain analyses of the reaction profiles reveal that the switch in preferred reactivity from substitution to elimination, if one goes from acidic to basic catalysis, is related to (1) the higher basicity of the deprotonated base, and (2) the change in character of the substrates LUMO from Cβ−H bonding in C2H5OH2+ to Cβ−H antibonding in C2H5OH.