bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Surface Roughness on Breakdown Voltage of 4H-SiC SBD with FLR Structure
Authors: Kinoshita Akimasa , Nishi Takashi , Ohyanagi Takasumi , Yatsuo Tsutomu , Fukuda Kenji , Okumura Hajime , Arai Kazuo
Published: March 2009

The Ti/4H-SiC Schottky barrier diodes with a field limiting ring (FLR) structure are fabricated. Two types of SBDs are prepared; one (SBD-A) is covered and another (SBD-B) isn’t covered with a carbon cap during high temperature annealing after ion implantation. The breakdown voltage at room temperature for SBD-A and SBD-B are 1400 V and 1000 V, respectively. The breakdown for both SBDs occurs due to an avalanche breakdown. The light emission images are obtained at the breakdown voltage by photo emission microscope (PEM). The light emission is observed along an FLR of the SBD-A as designed. On the other hand, the spot of light emission is observed on a FLR structure of the SBD-B. This light emission spot indicates that leakage current is concentrated because an electrical field concentration is generated at this one for the SBD-B. The root-mean-square roughness of the Al-implanted region on the FLR structure calculated from the atomic force microscopy (AFM) images for the SBD-A and the SBD-B are 0.697 nm and 5.58 nm, respectively. Therefore it is considered that large surface roughness on the FLR decreases breakdown voltage of SBD because an electrical field concentration is generated at a spot.
Doping Concentration Optimization for Ultra-Low-Loss 4H-SiC Floating Junction Schottky Barrier Diode (Super-SBD)
Authors: Ota Chiharu , Nishio Johji , Takao Kazuto , Hatakeyama Tetsuo , Shinohe Takashi , Kojima Kazu , Nishizawa Shin Ichi , Ohashi Hiromichi
Published: March 2009

Previous simulation works and experiments on the loss of 4H-SiC floating junction Schottky barrier diodes (Super-SBDs) show that the loss is related to the doping concentration in the drift region and the pattern of the floating layer. The effect of the doping concentration for lowering the loss is characterized the breakdown voltage (Vbd) and the on-state resistances (RonS) of the Super-SBDs based on Baliga’s figure of Merit (BFOM). Experimental devices with two doping concentrations in the drift region are fabricated to investigate the static characteristics: Vbd and RonS. The Vbd of the Super-SBDs is close to the simulation result, near 3000 V. However the tendency of the Vbd by the doping concentration is not similar to the simulation result. And the RonS are about 3.22 mcm2 which is higher than that of simulation result. The doping concentration optimized in this study does not show significant lowering loss and the design of the floating layer in the termination region affect the low-loss static characteristics of the Super-SBD. In addition, adopting PiN structure with floating layer (Super-PiN) affects the low-loss dynamic characteristics, optimizing the doping concentration in the drift region. We conclude that the fabricated Super-SBDs with the floating layer in the termination region, the drift region with a doping concentration of 1.01016 cm-3 and mesa-shaped termination structure, have excellent Vbd of 2990 V which is almost same as that of simulation result and RonS of 3.22 mcm2.
The Impact of Schottky Barrier Tunneling on SiC-JBS Performance
Authors: Dolny Gary M. , Woodin Richard L. , Witt T. , Shovlin J.
Published: March 2009

The impact of barrier tunneling on SiC-JBS performance is studied both experimentally and theoretically. We show that although the pinch-off effects associated with the JBS structure can significantly suppress the surface electric field, barrier tunneling still dominates the reverse behavior. Barrier tunneling determines the apparent breakdown voltage, as well as the apparent breakdown voltage vs. forward voltage drop trade-off of the JBS diode in practical applications.
Characterization of 4H-SiC Junction Barrier Schottky Diodes by Admittance vs Temperature Analyses
Authors: Raynaud Christophe , Nguyen Duy Minh , Brosselard Pierre , Pérez-Tomás Amador , Planson Dominique , Millan José
Published: March 2009

Schottky barrier diodes and junction barrier Schottky diodes are investigated by thermal admittance spectroscopy, and by Capacitance-Voltage measurements. Samples are protected with surrounding junction termination extension and p+ ring. Temperature dependence of the doping level is first calculated. Then admittance spectra allow detecting defects and extracting their activation energies and capture cross sections. Results seem to indicate the presence of interfacial defects and defects due to the implantation process.
Characterization of Phosphorus Implanted n+/p Junctions Integrated as Source/Drain Regions in a 4H-SiC n-MOSFET
Authors: Moscatelli Francesco , Nipoti Roberta , Poggi Antonella , Solmi Sandro , Cristiani Stefano , Sanmartin Michele
Published: March 2009

Phosphorous implanted n+/p diodes have been included in the masks for manufacturing n-MOSFET devices and processed in the same way of source/drain regions. The diode junctions were made by a P+ implantation at 300°C and a post implantation annealing at 1300°C. The diode emitter area was protected by 0.6 m thick CVD oxide during the processing of the MOSFET gate oxide. Three gate oxide processes were taken into account: two of them include a N implantation before a wet oxidation, while the third one was a standard oxidation. Considering the effect on the n+/p diodes, the main difference among the processes were the wet thermal oxidation time that ranged between 180 and 480 min at a temperature of 1100°C. The diode current-voltage characteristics show similar forward but different reverse curves in the temperature range of 25-290°C. Differences in reverse bias voltage as a function of the measurement temperature have been analyzed and are related to the different gate oxidation time. A correlation between the shortest oxidation time and the lower leakage current is presented.
Effect of Graphite Cap for Implant Activation on Inversion Channel Mobility in 4H-SiC MOSFETs
Authors: Naik Harsh , Tang K. , Chow T. Paul
Published: March 2009

The effects of using a graphite capping layer during implant activation anneal on the performance of 4H-SiC MOSFETs has been evaluated. Two sets of samples, one with the graphite cap and another without, with a gate oxide process consisting of a low-temperature deposited oxide followed by NO anneal at 1175°C for 2hrs were used for characterization. Various device parameters, particularly threshold voltage, subthreshold slope, field-effect mobility, inversion sheet carrier concentration and Hall mobility have been extracted for the two processes.
Diffusion Length in n-Doped 4H Silicon Carbide Crystals Detected by Alpha Particle Probe
Authors: Puglisi Donatella , Foti Gaetano , Bertuccio Giuseppe
Published: March 2009

The achievement of nuclear detectors in Silicon Carbide imposes severe constraints on the electronic quality and thickness of the material due to the relatively high value of the energy required to generate an electron-hole pair (7.8 eV) in this material compared to the value for Si (3.6 eV). In this work, 4H-SiC charged particle detectors were realised using epitaxial layers of n-type doping as active region. The thickness of the epilayer is always below 80 μm with a net doping concentration in the range of 8 x 1013 to 1016 cm-3. These properties allowed the fabrication of Schottky diodes that operate well as radiation detectors. At low doping concentration, the epilayer is totally depleted at quite low reverse bias (≈ 50 V), thereby obtaining the maximum active volume.
Positive Temperature Coefficient of Avalanche Breakdown Observed in a-Plane 6H-SiC Photodiodes
Authors: Soloviev Stanislav I. , Vert Alexey V. , Fronheiser Jody , Sandvik Peter M.
Published: March 2009

In this work, avalanche photodiodes (APDs) were fabricated using a-plane 6H- and 4H-SiC materials to investigate their electrical and optical properties. Temperature dependence of avalanche breakdown was measured. The diode structures were fabricated with positive angle beveling and oxide passivation to ensure a uniform breakdown across the device area. Despite the apparent presence of micro-plasmas, we observed that the breakdown voltage of a-plane 6H-SiC APDs increased with temperature suggesting a positive temperature coefficient.
Silicon Carbide UV Based Photovoltaic for Hostile Environments
Authors: Barker Simon , Stevens Rupert C. , Vassilevski Konstantin , Nikitina Irina P. , Wright Nicolas G. , Horsfall Alton B.
Published: March 2009

The development of silicon carbide technologies has allowed for the development of sensors and electronics to measure the changes in a variety of hostile environments. A problem has been identified with reliable and efficient ways to power such sensors in these hostile environments. It is likely to be impractical to run power cables to these sensors and battery power has a finite lifetime. Recent research has demonstrated many energy scavenging techniques but to date none have been developed with a view of operation in hostile environments. To investigate the power density achievable from a SiC based energy scavenging device a SiC pin diode was exposed to both broad spectrum light form a tungsten halogen bulb and a 255 nm UV source. IV and CV measurements were used to determine the structural properties and photovoltaic response of the device, dark saturation current, induced photo current and the fill factor. We present the characteristics and maximum power density of these devices at temperatures between 300 K and 600 K. We demonstrate that the maximum power density achievable decreases with temperature. This is mostly due to the reduction in the built in potential from the pn junction, and the reduction of the generated photocurrent.
Applications of SiC-Transistors in Photovoltaic Inverters
Authors: Kranzer Dirk , Burger Bruno , Navarro Nicolas , Stalter Olivier
Published: March 2009

Currently there are several silicon carbide (SiC) field effect or bipolar transistor types in development with normally-on and normally-off characteristics. It is not yet clear, which transistor type will prevail in the market and which will remain a niche product. This is not only determined by their electrical characteristics, but also by their acceptance by engineers. In this paper the implementation and the performance of 1200 V / 20 A / 100 m SiC-DMOSFETS and 1200 V / 12 A / 125 m normally-off SiC-JFETs in photovoltaic inverters (PV-inverters) is shown.
100 Amp, 1000 Volt Class 4H-Silicon Carbide MOSFET Modules
Authors: Losee Peter A. , Matocha Kevin , Arthur Steve , Delgado Eladio , Beaupre Richard , Pautsch A. , Rao R. Ramakrishna , Nasadoski Jeff , Garrett Jerome L. , Stum Zachary , Stevanovic Ljubisa , Conte Rosa Ana , Monaghan Keith
Published: March 2009

The development of large area, up to 70m/1kV (0.45cm x 0.45cm) 4H-SiC vertical DMOSFETs is presented. DC and switching characteristics of high-current, 100Amp All-SiC power switching modules are demonstrated using 0.45cm x 0.225cm DMOSFET die and commercial Schottky diodes. The switching performance from room temperature up to T=200°C of the All-SiC modules is presented, with as much as ten times lower losses than co-fabricated Si-based modules using commercial IGBTs.
Characterization and Modeling of SiC LTJFET for Analog Integrated Circuit Simulation and Design
Authors: Maralani A. , Mazzola Michael S. , Sheridan David C. , Sankin Igor , Bondarenko Volodymyr
Published: March 2009

The design of analog integrated circuits, for instance, the operational amplifiers, have been widely perfected with devices and processes available in silicon. However, analogous circuits have been the subject of research in Silicon Carbide (SiC). Among SiC devices, 4H-SiC Lateral-Trench JFET (LTJFET) transistor offers advantages and new opportunities to make affordable and reliable analog integrated circuits for harsh environment. In this paper: (1) SiC LTJFET is characterized for modeling and simulation, (2) effect of temperature variation on SiC LTJFET threshold voltage and small signal parameters are reported, (3) gain performance and small signal parameters of the basic analog circuit block, Common Source (CS) amplifier, based on the variation of the load transistors threshold voltage (Vth) are studied and analyzed, and (4) frequency and transient response of the cascoded CS amplifier (CS-Cas) are reported.
Composition and Interface Chemistry Dependence in Ohmic Contacts to GaN HEMT Structures on the Ti/Al Ratio and Annealing Conditions
Authors: Kolaklieva Lilyana , Kakanakov Roumen , Stefanov Plamen , Cimalla Volker , Maroldt S. , Ambacher Oliver , Tonisch Katja , Niebelschütz Florentina
Published: March 2009

Electrical, thermal and chemical properties of Ti/Al/Ti/Au ohmic contacts with different former Ti-Al ratio are investigated for application in GaN HEMTs. Lowest resistivity of 4.22x10-5 Ω.cm2 has been obtained to the channel of the HEMT structure. It is found out that the initial Ti/Al ratio influences the optimal annealing temperature at which the lowest resistivity is obtained and the element distribution and interface chemistry of the annealed contacts. XPS analysis revealed two compounds contributing to ohmic properties: an intermetal compound AlAu2 in the contact layer and a semimetal TiN at the interface with GaN.
Process Parameters Influence on Specific Contact Resistance (SCR) Value for TiAl Ohmic Contacts on GaN Grown on Sapphire
Authors: Ménard Olivier , Cayrel Frédéric , Collard Emmanuel , Alquier Daniel
Published: March 2009

In this work, Ti/Al bilayer sputtered ohmic contacts on n-type Gallium Nitride films were studied as a function of process parameters such as Ti thickness, surface cleaning procedure or annealing temperature. Epilayers, with doping concentration of 5.8x1018 at.cm-3, were grown on sapphire using AlN buffer layer. Electrical characterizations were made using circular Transfer Length Method (cTLM) patterns with a four probes equipment. Specific Contact Resistance (SCR) was then extracted for all the process conditions. Our results show that surface treatment is not a critical step in the ohmic contact process while annealing temperature has a larger impact. Finally, SCR values of 1x10-5 Ω.cm2 can be reproducibly achieved, which is of high interest for future devices fabrication using this material.
Influence of Thermal Annealing on Ohmic Contacts and Device Isolation in AlGaN/GaN Heterostructures
Authors: Roccaforte Fabrizio , Iucolano Ferdinando , Giannazzo Filippo , Moschetti Giuseppe , Bongiorno Corrado , Di Franco Salvatore , Puglisi Valeria , Abbondanza Giuseppe , Raineri Vito
Published: March 2009

Gallium nitride (GaN) and related alloys (AlxGa1-xN) are promising semiconductors for high-frequency and high-power devices applications. In particular, the growth of AlGaN/GaN heterostructures on SiC substrates, due to the high thermal conductivity of SiC, can lead to significant improvement in the device performances. An important issue in the fabrication of AlGaN/GaN devices is the influence of the required thermal budget (700-900°C) on the properties of Ohmic contacts and device isolation. In this work, the influence of thermal annealing on the fabrication of AlGaN/GaN devices was studied. Ti/Al/Ni/Au multilayers led to an Ohmic behavior with a specific resistance c in the 10-5 cm2 range upon annealing between 750°C and 850°C. The electrical behavior of Ohmic contacts was correlated with the evolution of the formed phases and with the temperature behavior of c. The stability of the inter-device isolation obtained by nitrogen-implantation during annealing at these temperatures was also monitored.
Low-Temperature Homoepitaxial Growth with SiCl4 Precursor Compared to HCl Assisted SiH4-Based Growth
Authors: Kotamraju Siva Prasad , Melnychuk Galyna , Koshka Yaroslav
Published: March 2009

Chlorinated silicon precursor SiCl4 was investigated as a source of additional chlorine instead of or in combination with HCl during the low temperature (13000C) halo-carbon epitaxial growth. No Si cluster cloud was visible inside the hot-wall susceptor indicating negligible homogeneous gas-phase nucleation. The growth rate was significantly enhanced compared to the SiH4-case, but was relatively close to the SiH4+HCl case. Similar to the SiH4+HCl growth, the increase of the growth rate caused by suppressed cluster formation was less significant than expected. The depletion of the growth species by vigorous polycrystalline deposition upstream of the hot zone, which was earlier reported for the SiH4+HCl growth, was also significant in the SiCl4-based growth. Closer to the growth zone, carbon species also get incorporated in the polycrystalline deposits.
Two Broadband GaN MMIC Power Amplifiers for EW Systems
Authors: Gonzalez-Garrido M. Angeles , Grajal Jesus , Cubilla Pablo , Lanzieri Claudio , Cetronio Antonio
Published: March 2009

This paper describes and evaluates two MMIC broadband high power amplifiers in the frequency band 2-6 GHz in microstrip technology. These amplifiers have scalable output-stage periphery of 4 and 8 mm. The amplifiers are based on 1 mm AlGaN/GaN high electron mobility transistor (HEMT) technology on SiC substrate. They were fabricated in the European foundry SELEX Sistemi Integrati, which has a gate process technology of 0.5 μm. The 4 mm amplifier has exhibited an output power of 15 W and the 8 mm of 28 W at Vds=25 V in pulsed conditions. The best power performance in continuous wave are 10.5 W and 15 W for 4 mm and 8 mm, respectively. Better than 20% PAE over the 2-6 GHz frequency range is achieved in CW.
Virus loads in Douglas-fir tussock moth larvae infected with the Orgyia pseudotsugata nucleopolyhedrovirus
Authors: Thorne Christine M. , Levin David B. , Otvos Imre S. , Conder Nicholas
Published: March 2009

We studied Orgyia pseudotsugata multiple nucleopolyhedrovirus (OpMNPV) infections in larvae of the Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough (Lepidoptera: Lymantriidae), to determine the quantity of OpMNPV particles that result in mortality. We observed a bimodal pattern of mortality in Douglas-fir tussock moth larvae that ingested diet plugs contaminated with 9.5 OpMNPV occlusion bodies. A mortality peak (80% of total mortality observed) occurred between day 5 and day 11 post ingestion, and a second, smaller mortality peak coincided with the onset of pupation. Virus loads, defined as the number of OpMNPV occlusion bodies in each sample of tested larval homogenate, were quantified using an indirect ELISA method. Virus loads that resulted in mortality were significantly greater than those quantified in larvae that were sacrificed during and after the peak mortality wave (P < 0.004 and P < 0.0001, Mann–Whitney U two-tailed rank test and SPSS®, respectively). This is the first known attempt to differentiate the quantity of virus produced during lethal infections from the virus loads in larvae that survive infection.
Re-analysis of pheromone-mediated aggregation behaviour of European earwigs
Authors: Hehar Gagandeep , Gries Regine , Gries Gerhard
Published: March 2009

Aggregation of the European earwig, Forficula auricularia L. (Dermaptera: Forficulidae), is known to be, in part, a response to aggregation pheromone. However, many aspects of pheromone biology remain unknown or controversial. In two-choice experiments with field-collected specimens in a still-air olfactometer, we determined that female, male, and juvenile F. auricularia all produce and respond to aggregation pheromone and that the pheromone is perceived by means of olfaction. Various sources (or extracts thereof) reportedly containing or emitting pheromone (including the insects’ integument, tibiae, or fecal excreta) did not induce significant responses. Our data suggest that none of these sources contains all or any of the essential pheromone components. These controversial results may be due to differences in (i) experimental procedures, such as single- or grouped-insect bioassays, or (ii) developmental stages of the bioassay insects. It is conceivable that juveniles and adults produce and respond to different components of aggregation pheromone.
Brief communication: Rethinking the impact of the 1918 influenza pandemic on sex differentials in mortality
Authors: Sawchuk L.A.
Published: March 2009

This study will assess the general impact of the 1918 influenza on overall mortality and its impact on mortality attributable to pulmonary tuberculosis in a small‐scale population. Using life table and decomposition methodologies, changes in mortality in Gibraltar used a scheme that identified a pre‐epidemic period (1904–1917), the epidemic year (1918), and the post‐epidemic period (1919–1927). Overall health in both sexes fell significantly in 1918 with a drop in life expectancy at birth, however, health quickly rebounded in the post‐epidemic period. In the case of women, there was a significant increase in life expectancy at birth after the epidemic. The impact of influenza on the magnitude of sex differentials in the life expectancy at birth fell during epidemic year but returned to a level comparable to that of the pre‐epidemic period. With respect to respiratory tuberculosis deaths, the immediate impact of influenza was restricted to only a significant increase in the rate among women (aged 15–54). In the post‐epidemic period, tuberculosis mortality rates returned to the pre‐epidemic state in both sexes. The findings from Gibraltar stand in contrast opposition to results reported for experience in the United States during the 1918 flu. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.
How an arbitration provision, carefully constructed, ended up defeating itself by leading to multiple court proceedings
Authors: Nissen William J.
Published: March 2009

Is there such a thing as being too precise when crafting an arbitration alternative to litigation? Where a merger agreement produced four arbitration forums for different types of disputes, the answer is a resounding “Yes!” William J. Nissen, of Chicago, explains the litigious, still‐unresolved matter.
C(Aryl)‐O‐Aktivierung von Arylcarboxylaten in nickelkatalysierten Biarylsynthesen
Authors: Gooßen Lukas J. , Gooßen Käthe , Stanciu Corneliu
Published: March 2009

Fast zeitgleich erzielten zwei Arbeitsgruppen einen Durchbruch bei der Aktivierung der C(Aryl)‐O‐Bindung von Phenolderivaten (siehe Schema; Cy=Cyclohexyl): Garg et al. kuppelten Arylpivalate mit Arylboronsäuren zu unsymmetrischen Biarylen. Shi et al. gelang eine solche Kreuzkupplung unter C(Aryl)‐O‐Aktivierung für Arylester verschiedener Carbonsäuren, wobei die besten Ergebnisse bei der Kupplung mit Arylboroxinen erneut mit Arylpivalaten erzielt wurden.

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Synthesis, characterization and crystal structure of a novel Ni(II) coordination polymer with dipyrido[3,2‐a:2′,3′‐c]phenazine and 4,4′‐oxy(bisbenzoate)
Authors: Qiao Qian , Wang Ruguo , Wu Guoqiang , Tang Tiandi
Published: March 2009

A novel coordination polymer, [Ni(dppz)(oba)(H2O)]·0.5H2O (dppz = dipyrido[3,2‐a:2′,3′‐c]phenazine and oba = 4,4′‐oxy(bisbenzoate)) has been synthesized through hydrothermal method and characterized by IR, and single‐crystal X‐ray diffraction. It crystallizes in monoclinic, space group C2/c with a = 23.163(5), b = 18.211(4), c = 14.460(3) Å, α = γ = 90°, β = 100.45(3)°, V = 5998(2) Å3, Z = 2. The structure was solved by direct methods and refined to R = 0.0866 (wR2 = 0.1836). The compound exhibits interesting one‐dimensional chain structures, which are further stacked through π‐π interactions to form supramolecular double chains. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of epitaxial laterally overgrown silicon structures by high resolution x‐ray rocking curve imaging
Authors: Heimbrodt B. , Lübbert D. , Köhler R. , Boeck T. , Gerlitzke A.‐K. , Hanke M.
Published: March 2009

Spatially resolved rocking curve imaging has been used to analyze laterally overgrown silicon layers grown by liquid phase epitaxy. We were able to study both the overgrown layer as well as the strain fluctuations of the Si substrate underneath by means of a tabletop x‐ray topographic setup. The strain‐field analysis reveals relative changes of the lattice parameter up to 3.5×10‐6 in the silicon substrate underneath the overgrown layer in particular regions and a down bending of both wings of the epitaxial overgrown layers. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hippocampal lesions impair spatial memory performance, but not song—A developmental study of independent memory systems in the zebra finch
Authors: Bailey David J. , Wade Juli , Saldanha Colin J.
Published: March 2009

Songbirds demonstrate song‐ and spatial‐learning, forms of memory that appear distinct in formal characteristics and fitting the descriptions and criteria of procedural and episodic‐like memory function, respectively. As in other vertebrates, the neural pathways underlying these forms of memory may also be dissociable, and include the corresponding song circuit and hippocampus (HP). Whether (or not) these two memory systems interact is unknown. Interestingly, the HP distinguishes itself as a site of immediate early gene expression in response to song and as a site of estrogen synthesis, a steroid involved in song learning. Thus, an interaction between these memory systems and their anatomical substrates appears reasonable to hypothesize, particularly during development. To test this idea, juvenile male or female zebra finches received chemical lesions of the HP at various points during song learning, as did adults. Song structure, singing behavior, song preference, and spatial memory were tested in adulthood. Although lesions of the HP severely compromised HP‐dependent spatial memory function across all ages and in both sexes, we were unable to detect any effects of HP lesions on song learning, singing, or song structure in males. Interestingly, females lesioned as adults, but not as juveniles, did lose the characteristic preference for their father's song. Since compromise of the neural circuits that subserve episodic‐like memory does very little (if anything) to affect procedural‐like (song learning) memory, we conclude that these memory systems and their anatomical substrates are well dissociated in the developing male zebra finch. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009
Antibacterial activity and bonding ability of an adhesive incorporating an antibacterial monomer DMAE‐CB
Authors: Xiao Yu‐Hong , Ma Sai , Chen Ji‐Hua , Chai Zhi‐Guo , Li Fang , Wang Ying‐Jie
Published: March 2009

This study evaluated the antibacterial effect and microtensile bond strength of a resin‐based adhesive containing an antibacterial monomer DMAE‐CB (methacryloxylethyl cetyl dimethyl ammonium chloride). Cured specimens of 1, 2, and 3% DMAE‐CB‐containing Single Bond 2 (crosslinking monomer: Bis‐GMA, dimethacrylates; functional monomer: HEMA) were prepared, and their antibacterial effects on Streptococcus mutans ATCC 25175 were investigated. Antibacterial property after 0, 30, 90, and 180 days of aging was also tested. Bonding ability of the experimental adhesive incorporating 3% DMAE‐CB was evaluated by microtensile bond strength test. The cured experimental adhesive exhibited an inhibitory effect on S. mutans growth, and the adhesive containing 3% DMAE‐CB showed higher antibacterial efficiency compared with those incorporating 1 or 2% anibacterial monomer. Antibacterial activities of the specimens lasted for at least 180 days. Microtensile bond strength test revealed that the bonding ability of the experimental adhesive was not significantly adversely affected by the incorporation of DMAE‐CB. Therefore, dental adhesives with strong and long‐lasting bacteriostatic property could be achieved by incorporating DMAE‐CB without negatively influencing bonding ability. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2009
A convenient synthesis of N‐aryl‐1,2‐dihydro‐2‐oxo‐3‐pyridinecarbox‐amides, N‐aryl‐N‐methyl‐1,2‐dihydro‐2‐oxo‐3‐pyridinecarboxamides and their 1‐methyl (O‐methyl)‐derivatives
Authors: Cativiela C. , Fernandez J. , Melendez E.
Published: March 2009

A new and versatile method for the preparation of the isonixine analogues, N‐aryl‐1,2‐dihydro‐2‐oxo‐3‐pyridinecarboxamides and N‐aryl‐N‐methyl‐1,2‐dihydro‐2‐oxo‐3‐pyridinecarboxamides is described via the selective chlorination of 2‐hydroxynicotinic acid. In order to prepare these new compounds, the chemistry of the methyl‐blocked forms of each tautomer is discussed.
Synthesis of benzonaphthyridines
Authors: Godard Alain , Quéguiner Guy
Published: March 2009

A large number of benzonaphthyridines have been synthesized from o‐aminoformylquinolines substituted on the pyridine ring by use of the Friedlander cyclization.
[1,2,4]Triazines. 4. Regiospecific ring closure reactions involving 6‐amino‐5‐hydrazino[1,2,4]triazin‐3(2H)‐ones and orthoesters
Authors: Lovelette C. A. , Geagan K.
Published: March 2009

6‐Amino‐5‐hydrazino[1,2,4]triazin‐3(2H)‐one, 3, was treated with a variety of orthoesters and concentrated acid forming mixtures of ring‐closed and open‐chain derivatives. These mixtures were converted in warm aqueous acid to the Mriazolo[5,1‐d][1,2,4]triazin‐3(2H)‐ones, 11b, 14b, and 15b by a regiospecific ring closure at N‐4 of the [1,2,4]triazine ring and subsequent Dimroth‐like rearrangement of the initially formed s‐triazolo[4,3‐d][1,2,4]triazin‐3(2H)‐ones (11a, 14a, 15a).
Methylpyridylbenzimidazoles. Part I. Mono, bis‐quaternary salts and related polymethyne dyes
Authors: Barni Ermanno , Savarino Piero , Viscardi Guido , Pelizzetti Ezio
Published: March 2009

The reaction of 2‐(4‐methyl‐2‐pyridyl)benzimidazole with long chain alkyl halides led to N‐alkylation at the imidazole ring. The bases obtained were selectively quaternized at the azine and azole nitrogen atoms. The pyridinium salts gave the corresponding polymethyne dyes. Spectral (nmr and uv) and surface properties are briefly discussed.
Methylpyridylbenzimidazoles. Part II. Bridged mono and bis‐quaternary salts
Authors: Barni Ermanno , Savarino Piero , Viscardi Guido , Pelizzetti Ezio
Published: March 2009

The reaction of 2‐(4‐methyl‐2‐pyridyl)benzimidazole and of its N long alkyl chain derivatives with 1,3‐dibromopropane led to cyclic bis‐charged salts. Their spectroscopic (nmr and uv) and surface properties are briefly discussed. It turned out to be interesting to compare the similar behaviour of these salts and the corresponding well known derivatives of 2,2′‐bipyridyl.
The reaction of dihydroxyacetone with ethanedithiol. Synthesis and x‐ray crystal structure of 1,4,7,10‐tetrathiaspiro[5.5]undecane
Authors: Hamor T. A. , Jones A. S. , Jones R. H. , Mcguigan C. , Walker R. T.
Published: March 2009

Reaction of dihydroxyacetone with an excess of ethanedithiol in the presence of 10M hydrochloric acid gives 2,2‐di(hydroxymethyl)‐1,3‐dithiacyclopentane (1) in low yield. When boron trifluoride etherate is used instead of hydrochloric acid, the same reactants give 1,4,7,10‐tetrathiaspiro[5. 5]undecane (3). The structure of the latter was established by X‐ray crystallography. The crystals are monoclinic, space group P2,/n, with a = 6.31(1), b = 21.57(2), c = 7.61(1)Å, β = 102.2(1)° and Z = 4, R = 0.038 for 2289 reflections. The two 1,4‐dithiane rings in 3 are significantly more puckered than normal cyclohexane rings. The uv spectrum of 3 is consistent with values reported for other sulphides and with the X‐ray structure.
Synthèse d'analogues bihétérocycliques du phénanthrène: Les méthyl‐1‐[1]benzothinéo, benzoséléno[2,3‐b ]pyrroles, et méthyl‐1‐[1]benzofuro, benzothiéno et benzoséléno[3,2‐b ]pyrroles
Authors: Webert Jean‐Marie , Cagniant Denise , Cagniant Paul , Kirsch Gilbert , Weber Jean‐Victor
Published: March 2009

La condensation du sarcosinate d'éthyle sur les halogeno‐2 (ou ‐3) formyl‐3 (ou ‐2) [l]benzofuranne, benzo‐thiophéne et benzosélénophéne de měme que sur les 2H‐[1]benzohétérocyclariones‐3 correspondantes a été etudiee. Dans ce dernier cas, le composé obtenu est ensuite formylé et cyclodeshydraté. Ont été ainsi synthétisés les méthyl‐l‐[l]benzothiéno, benzoséléno[2,3‐b]pyrroles et les méthyl‐1‐[1]benzofuro, benzothiéno et benzoséléno[3,2‐6]pyrroles.
13C NMR studies on dibenz[b,f]azepines
Authors: Molock Frank F. , Boykin David W.
Published: March 2009

The assignment of the 13C nmr resonances of six dibenz[b,f]azepines (1‐6) in dimethylsulfoxide‐d6 was made using chemical shift arguments, coupling to a fluorine substituent, selective proton decoupling, and fully coupled spectra. Exchange of the heterocyclic N‐H with deuterium simplified and clarified the coupled spectrum of 1.
One step synthesis of 3‐cyano‐4‐(5‐nitrobenzothienyl)pyridines and 3‐Cyano‐4‐(5‐nitrobenzothienyl)pyridin‐2‐ones for biological evaluation
Authors: Zayed S. M. A. D. , Attia A.
Published: March 2009

A new one‐vessel reaction has been developed for the synthesis of substituted aminocyanopyridines 2 and cyanopyridin‐2‐ones 3. Compounds 2a‐c and 3a‐c were readily obtained by heating molar amounts of 5‐nitro‐benzothiophene‐2‐carboxaldehyde 1, the appropriate acetyl derivative and the active methylene compound (malononitrile or ethyl cyanoacetate) in presence of ammonium acetate. The new method had the advantage of being quick, economic and of general application. A possible mechanism for the reaction, has been suggested.
4‐(2‐di‐n‐propylaminoethyl)‐7‐methoxyindole
Authors: Cannon Joseph G. , Lukszo Jan , Max George A.
Published: March 2009

Preparation of the title compound has been achieved by a modification of the Reissert indole synthesis, starting with 2‐nitro‐3‐methyl‐4‐cyanoanisole (3), and homologation of the CN group of the resulting 4‐cyano‐7‐methoxyindole. The starting material 3 was prepared by bromination of 2‐nitro‐3‐methylphenol, and the structure of the bromination product was verified chemically.
3‐Oxo‐1,2‐benzoisothiazoline‐2‐acetic acid 1,1‐dioxide derivatives. II. Reaction of amides with alkoxides
Authors: Perillo Isabel A. , Schapira Celia B. , Lamdan Samuel
Published: March 2009

Reaction of some 3‐oxo‐1,2‐benzoisothiazoline‐2‐acetamide 1,1‐dioxides (1a‐f) with alkaline alkoxides was carried out under various conditions. Under mild conditions, 1a‐f with sodium methoxide gave o‐(N‐carbox‐amidomethylsulfamyl)benzoic acid methyl esters (2a‐f, R = CH3). Compounds 1a or 2a reacted with sodium alkoxides under drastic conditions affording only ester 5. Under the same conditions, 1b‐d or 2b‐d gave 4‐hydroxy‐2H‐1,2‐benzothiazine‐3‐carboxamide 1,1‐dioxides (3b‐d), while 1e‐f or 2e‐f afforded the acid 6 in variable amounts, together with the expected benzothiazines 3e‐f. Isolation of ethyl ether as another product in the reaction of 1e‐f with sodium ethoxide supports the suggestion that the formation of 6 involves the O‐alkyl fission on the alkyl carbon of the esters 2e‐f. An explanation of these results may be related to the acidic character of the amide hydrogen in compounds 2e‐f.
A modified bischler‐napieralski reaction. Synthesis of 2,3,4,9‐ tetrahydro‐1H‐pyrido[3,4‐B]indole derivatives and their base‐catalyzed transformation to N‐acetyl‐N‐[2‐[1 ‐acetyl‐2‐[1 ‐(acetyloxy)‐1‐propenyl]‐ 1H‐indol‐3‐yl]ethyl]acetamides
Authors: Bobowski George
Published: March 2009

The treatment of N‐[2‐(1H‐indol‐3‐yl)ethyl]alkanamide, 1 (1), with phosphorus oxychloride under controlled conditions gave l‐alkyl‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐1‐ol, 2. The reaction of 2 with acetic anhydride or with methyl isocyanate at room temperature resulted in the formation of amido carbinol 3 and urea carbinol 7, respectively. The former was transformed into amido ester 4 by boiling acetic anhydride. When the reaction of 3 with acetic anhydride was carried out in the presence of excess triethylamine at 105°, C‐N bond cleavage of the tetrahydropyridine ring took place with concurrent bis(N‐acetylation) to give the enol ester derivative 5. The structures of all compounds are consistent with chemical and spectral evidence.
Synthesis of analogues of the 2,3,6,‐triazaphenothiazine ring system
Authors: Okafor Charles O. , Castle Raymond N.
Published: March 2009

Treatment of 2,3‐dichloroquinoxalines with 2‐amino‐6‐picoline‐3‐thiol gave a mixture of 2,3‐bis(2‐amino‐6‐picolinyl‐3‐thio)quinoxalines (16, R = H, CI) and 2,3‐bis (N,N‐dimethylamino)quinoxalines (15, R = H, CI) separated by fractional crystallization. A similar reaction of 3‐amino‐6‐methoxypyridine‐2(1H)‐thione (9) with 4,5‐dichloropyridazin‐3(2H)‐one (21) gave 4‐chloro‐5‐(3‐amino‐6‐methoxypyridyl‐2‐thio)pyridazin‐3(2H)‐one (22). Concentrated hydrochloric acid‐catalysed cyclization of 22 gave the non‐rearranged 7‐methoxy‐2,3,6‐triazaphenothiazin‐1(2H)‐one. The action of compound 22 in refluxing glacial acetic acid gave, on the other hand, 7‐methoxy‐2,3,6‐triazaphenothiazin‐4(3H)‐one via a Smiles rearrangement. These cyclized compounds are the first known derivatives of the new 2,3,6‐triazaphenothiazine ring system.
Antimykotische wirkstoffe. XV. . Die halogensubstitution bei phenoxy‐1,3,5‐triazinen
Authors: Kreutzberger Alfred , Richter Barbara
Published: March 2009

Durch die nucleophile substitution eines Chloratoms in 2, 4‐Dichloro‐6‐diethylamino‐1, 3, 5‐triazine (1) mittels Halogenphenolen (2a‐f) werden die 2‐chloro‐4‐diethylamino‐6‐halogenphenoxy‐1, 3, 5‐triazine (3a‐f) zugänglich. In Strukturtyp 3 finden sich Vertreter mit antimykotischer Wirksamkeit.
Metallations of 5 H‐dibenz [b, f] azepine and 10,11‐dihydro‐5H‐dibenz [b, f] azepine. Synthesis of 4‐substituted derivatives
Authors: Dahlgren T. , Hallberg A. , Helitzer R. , Martin A. R.
Published: March 2009

The synthesis of 4‐substituted 5 H‐dibenz [b, f] azepines and 10, 11‐dihydro‐5 H‐dibenz [b, f] azepine resulting from the reaction of the corresponding 4, 5‐dilithio derivatives and different N, N‐dimethylamides is reported. The total assignment of the pmr spectra of the prepared formyl derivatives based on decoupling experiments is also described.
The synthesis of macrocyclic polyether‐diester ligands containing a long‐chain alkoxy substituted pyridine subcyclic unit
Authors: Bradshaw Jerald S. , Spencer Neil O. , Hansen Gilbert R. , Izatt Reed M. , Christensen James J.
Published: March 2009

Two new series of macrocyclic polyether‐diester ligands have been prepared containing 4‐pentoxy‐ and 4‐octoxypyridine subcyclic units. The 4‐alkoxy‐2, 6‐pyridinedicarboxylic acid derivatives used as starting materials were prepared from 4‐chloro‐2, 6‐pyridinecarbonyl chloride. The 4‐octoxydiketopyridino‐18‐crown‐6 ligand greatly facilitates the transport of silver ions across a chloroform liquid membrane.
Concerning the preparations of some pyridylimidazothiazole derivatives
Authors: Eichler Eva , Rooney C. Stanley , Williams Haydn W. R.
Published: March 2009

The preparations of some 4‐pyridylimidazo[2,1‐b]thiazole and ‐imidazo[5,1‐b]thiazole derivatives are described. In some of the cyclizations to form the imidazothiazole ring systems, trifluoroacetic anhydride, the dehydration reagent employed, participated in the reaction leading to products bearing a trifluoromethyl or trifluoroacetyl substituent.
Synthesis of s‐3‐indolemethyl derivatives of 5′‐deoxy‐5′‐thioadenosine
Authors: Benghiat Eric , Crooks Peter A.
Published: March 2009

The S‐3‐(1‐methylindole)methyl and S‐3‐(1,2‐dimethylindole)methyl derivatives of 5′‐deoxy‐5′‐thioadenosine have been prepared by reaction of the appropriate 3‐indolemethylthioacetate with 5′‐deoxy‐5′‐chloro‐adenosine in basic media. 5′‐Deoxy‐5′‐(3‐indolemethylthio)adenosines unsubstituted at the indolic nitrogen, cannot be prepared via this route due to facile conversion of the precursor 3‐indolemethylthiol derivative to the corresponding 3,3′‐diindolemethyl sulfide.
Synthèse et détermination de la structure de la 3H‐(indazolyl‐3′)‐5 oxadiazol‐1,3,4‐one‐2 par RMN 13C et spectrometrie de masse
Authors: Robba Max , Lancelot Jean‐Charles , Maume Daniel , Rabaron Alain
Published: March 2009

La synthèse de la 3H (indazolyl‐3′)‐5 oxadiazol‐1,3,4 one‐2 (2) est effectuée par cyclisation de l'hydrazide de l'acide indazole‐3 carboxylique (3) avec l'oxychlorure de carbone. La détermination de la structure est réalisée grâce à une étude comparative par rmn du 13C et par spectrométrie de masse avec la 2H, 3H‐triazino‐1,2,4‐[4,5‐b]indazoledione‐1,4 (1). Un réarrangement en 2 précède la fragmentation de 1 sous l'impact électronique.
Oxidation of bis‐arylhydrazones of 3,3‐dimethylpentane‐2,4‐dione with silver oxide
Authors: Stephanidou‐Stephanatou J.
Published: March 2009

Oxidation of the title bis‐arylhydrazones 2 with silver oxide gives 1‐aryl‐5‐arylazo‐3,4,4,5‐tetramethyl‐2‐pyrazolines 4 in almost quantitative yield. The spectral data of the pyrazolines 4 as well as the reaction mechanism are discussed.
Ring transformation of 8‐bromo‐1,7‐phenanthroline in reaction with potassium amide/liquid ammonia
Authors: van den Haak Henk J. W. , Bouw Jan P. , van der Plas Henk C.
Published: March 2009

Reaction of 8‐bromo‐1,7‐phenanthroline with potassium amide in liquid ammonia gives besides the corresponding 8‐amino compound 2‐methyl‐1,3,5‐triazaphenanthrene. In this ring transformation 7‐ethynyl‐aminoquinoline‐8‐aldimine is involved as intermediate, as proved by nmr spectroscopy.
Benzomorphan related compounds. XVII . Oxidative cyclization of N‐arylethyl‐6, 7‐benzomorphans
Authors: Bosch Joan , Domingo Antonio , Granados Ricardo
Published: March 2009

The synthesis of two new bridged polycyclic systems (I and II), possessing a rigid N‐arylethylbenzomorphan structure, by mercuric acetate cyclization of the corresponding seco derivatives (IV and VI, respectively) is described. The relative configuration of these compounds and the preferred indolo[2, 3‐a]‐ or benzo[a]quin‐olizidine conformation is assigned.
Bimanes. 19. Characteristics of the molecular structures of 1,5‐diazabicyclo[3.3.0]octadienediones (9,10‐dioxabimanes) determined by x‐ray crystallography
Authors: Goldberg Israel , Bernstein Joel , Kosower Edward M. , Goldstein Ehud , Pazhenchevsky Barak
Published: March 2009

The molecular structures of a variety of 1, 5‐diazabicyclo[3.3.0]octadienediones (9, 10‐dioxabimanes), including three 9, 10‐dioxa‐syn‐bimanes, three 4, 6‐bridged 9, 10‐dioxa‐syn‐bimanes, and three 9, 10‐dioxa‐anti‐bimanes, as determined by x‐ray crystallography, are analyzed and compared with respect to planarity, bond distances, bond angles and intermolecular packing. “Planarity” may be the resultant of two non‐planar equilibrium forms, a conclusion based on the anisotropic thermal motion parameters of the central N‐N bond. “Amide”‐type conjugation (N‐C=O) is important in all planar bimanes; peripheral conjugation (N‐C=C‐C = O) is more significant in planar syn‐bimanes and decreased conjugation is evident in the bent bridged syn‐bimanes. Weak CH…O bonds contribute significantly to the crystal packing arrangements.
Herstellung und reaktivität von alkoxy‐1‐azafulvenen
Authors: Stachel Hans‐Dietrich , Poschenrieder Hermann , Immerz‐Winkler Elisabeth
Published: March 2009

Die Titelverbindungen 7‐9 reagieren mit Nucleophilen an der Lactimethergruppe, während bei 6 Umsetzungen in 4‐Stellung, bei der bromierten Verbindung 14 in 4‐ wie auch in 6‐Stellung möglich sind.
2‐Acyloxypyrazines. Convenient acylating agents for amines
Authors: Ohta Akihiro , Shimazaki Makoto , Tamamura Hideo , Mamiya Yukari , Watanabe Tokuhiro
Published: March 2009

2‐Acyloxypyrazines were found to be useful acylating reagents for amines. The preference of the acylation was for primary amines rather than secondary ones and also for aliphatic amines rather than aromatic ones.
Preparation of hexa‐, penta‐ and tetraphenyl‐2,6‐ and ‐2,7‐naphthyridines
Authors: Mataka Shuntaro , Takahashi Kazufumi , Tashiro Masashi
Published: March 2009

Di‐ and triphenyldibenzoylpyridines (1) were prepared by the condensation reaction of 3, 4‐dibenzoyl‐2, 5‐diphenylthiophene (2) with methylamine derivatives 3 and by the subsequent oxidative ring cleavage of the resultant thieno[3, 4‐c]pyridines 4. The reaction of 1 with 3 afforded polyphenyl‐2, 6‐ (5) and ‐2, 7‐naphthyridines (6).
Structure of hexacyclen salts 1,4,7,10,13,16‐hexaazacyclooctadecanehexahydrogennitratemonohydrte
Authors: Margulis T. N. , Zompa L. J.
Published: March 2009

The crystal structure of the anion‐complexing agent, 1, 4, 7, 10, 13, 16‐hexaazacyclooctadecanehexahydrogen‐nitratemonohydrate, has been determined by a single‐crystal x‐ray diffraction study. Nitrate and water are bound strongly to the hexacyclen ring by hydrogen‐bonds and ion‐ion interactions. The hexacyclen ring has a conformation which is relatively independent of its crystallographic environment.
Synthesis and acylating properties of 4,5‐dihydro‐6H‐1,3,4‐ oxadiazin‐6‐ones
Authors: Farina Carlo , Pifferi Giorgio , Nasi Ferdinando , Pinza Mario
Published: March 2009

Cyclization of α‐acylhydrazinoacids with dicyclohexylcarbodiimide or with acetic anhydride allows an easy entry to the little known class of 4, 5‐dihydro‐6H‐1, 3, 4‐oxadiazin‐6‐ones. Such compounds maintain the optical activity of the starting hydrazino acids and may be exploited as useful acylating agents.
Synthesis and spectral properties of the 1‐aryl‐2‐phenyl‐4‐oxo‐4,5,6,7‐tetrahydroindole oximes and of their beckmann rearrangement products
Authors: Dagher C. , Hanna R. , Terentiev P. B. , Boundel Y. G. , Maksimov B. I. , Kulikov N. S.
Published: March 2009

Under Beckmann conditions the oximes of the 1‐aryl‐2‐phenyl‐4‐oxo‐4,5,6,7‐tetrahydroindoles 2a‐k are rearranged yielding as the sole product, 1‐aryl‐2‐phenyl‐4‐oxo‐1,4,5,6,7,8‐hexahydropyrrolo[3,2‐c]azepine 3a‐k. The spectral data (ir, uv, ms) of these two classes of compounds are also discussed.
Synthesis of some 1‐hydroxy derivatives of 4‐ and 6‐azaindole analogues
Authors: Daisley Roy W. , Hanbali Jafar R.
Published: March 2009

1‐Hydroxy‐4‐azaindole and 1‐hydroxy‐4‐(and 6)‐azaindol‐2(3H)‐one derivatives are novel compounds and a facile synthesis by the reductive cyclisation of substituted 3‐nitropyridines is described. Problems associated with the catalytic hydrogenation of the parent nitro compounds are also discussed.
Unequivocal synthesis of 2,3,6‐triazaphenothiazine and two new tetraazaphenothiazine heterocycles
Authors: Okafor Charles O. , Castle Raymond N. , Wise Dean S.
Published: March 2009

This paper describes the unequivocal synthesis of three new heterocycles: 2, 3, 6‐triazaphenothiazine (7) and 2, 3, 6, 9‐tetraazaphenothiazine (18), both parents of the respective ring systems and the 6, 8‐dihydro‐7, 9‐di‐oxo derivative of 2, 3, 6, 8‐tetrahydrophenothiazine (12). These compounds were obtained by base‐catalysed condensation of 4, 5‐dichloropyridazine (8) with the appropriate o‐amino‐heterocyclic thiols 9, 11, 16. In contrast, reaction of 2, 3, 5‐trichloropyrazine (20) with 4, 6‐diaminopyrimidine‐5‐thiol (21) and 2‐amino‐6‐picoline‐3‐thiol (28) gave 5‐chloro‐2, 3‐bis(diaminopyrimidinyl‐5‐thio)pyrazine (33) and 5‐chloro‐2, 3‐bis(2‐amino‐6‐picolinyl‐3‐thio)pyrazine (29), respectively. Chloropyrazine (34) and 3‐aminopyridine‐2(1H)‐thione (9) followed the latter reaction path to 2‐(3‐amino‐2‐pyridyl) pyrazinyl sulfide (35) in good yields. Structural assignments were based on their infrared, ultraviolet, nmr and mass spectra.
The synthesis of four isomeric bisthienothiepinones
Authors: Charonnat Jeffrey A. , Muchowski Joseph M. , Nelson Peter H.
Published: March 2009

The displacement reaction between sodium thiophene‐3‐thiolate and methyl 3‐(bromomethyl)thiophene‐2‐carboxylate (5) gave the expected thioether 7a. Basic hydrolysis afforded the carboxylic acid 7b; conversion to the acid chloride, and treatment of the latter with stannic chloride then produced the bisthienothiepinone 1. Using analogous reactions the isomers 2‐4 were also synthesized.