Rapid Generation of Molecular Complexity in the Lewis or Brønsted Acid-Mediated Reactions of Methylenecyclopropanes

Although they are highly strained, methylenecyclopropanes (MCPs) are readily accessible molecules that have served as useful building blocks in organic synthesis. MCPs can undergo a variety of ring-opening reactions because the release of cyclopropyl ring strain (40 kcal/mol) can provide a thermodynamic driving force for reactions and the π-character of the bonds within the cyclopropane can afford the kinetic opportunity to initiate the ring-opening. Since the 1970s, the chemistry of MCPs has been widely explored in the presence of transition metal catalysts, but less attention had been paid to the Lewis or Brønsted acid mediated chemistry of MCPs. During the past decade, significant developments have also been made in the Lewis or Brønsted acid mediated reactions of MCPs. This Account describes chemistry developed in our laboratory and by other researchers.Lewis and Brønsted acids can be used as catalysts or reagents in the reactions of MCPs with a variety of substrates, and substituents on the terminal methylene or on the cyclopropyl ring of MCPs significantly affect the reaction pathways. During the past decade, we and other researchers have found interesting transformations based on this chemistry. These new reactions include the ring expansion of MCPs, cycloaddition reactions of MCPs with aldehydes and imines, cycloaddition reactions of MCPs with nitriles in the presence of strong Brønsted acid, radical reactions of MCPs with 1,3-dicarbonyl compounds, intramolecular Friedel–Crafts reactions of MCPs with arenes, acylation reactions of MCPs, and the reaction of MCPs with 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers.These Lewis or Brønsted acid mediated reactions of MCPs can produce a variety of new compounds such as cyclobutanones, indenes, tetrahydrofurans, and tetrahydroquinolines. Finally, we have also carried out computational studies to explain the mechanism of the Brønsted acid mediated reactions of MCPs with acetonitrile

Rapid Generation of Molecular Complexity in the Lewis or Brønsted Acid-Mediated Reactions of Methylenecyclopropanes

Although they are highly strained, methylenecyclopropanes (MCPs) are readily accessible molecules that have served as useful building blocks in organic synthesis. MCPs can undergo a variety of ring-opening reactions because the release of cyclopropyl ring strain (40 kcal/mol) can provide a thermodynamic driving force for reactions and the π-character of the bonds within the cyclopropane can afford the kinetic opportunity to initiate the ring-opening. Since the 1970s, the chemistry of MCPs has been widely explored in the presence of transition metal catalysts, but less attention had been paid to the Lewis or Brønsted acid mediated chemistry of MCPs. During the past decade, significant developments have also been made in the Lewis or Brønsted acid mediated reactions of MCPs. This Account describes chemistry developed in our laboratory and by other researchers.Lewis and Brønsted acids can be used as catalysts or reagents in the reactions of MCPs with a variety of substrates, and substituents on the terminal methylene or on the cyclopropyl ring of MCPs significantly affect the reaction pathways. During the past decade, we and other researchers have found interesting transformations based on this chemistry. These new reactions include the ring expansion of MCPs, cycloaddition reactions of MCPs with aldehydes and imines, cycloaddition reactions of MCPs with nitriles in the presence of strong Brønsted acid, radical reactions of MCPs with 1,3-dicarbonyl compounds, intramolecular Friedel–Crafts reactions of MCPs with arenes, acylation reactions of MCPs, and the reaction of MCPs with 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers.These Lewis or Brønsted acid mediated reactions of MCPs can produce a variety of new compounds such as cyclobutanones, indenes, tetrahydrofurans, and tetrahydroquinolines. Finally, we have also carried out computational studies to explain the mechanism of the Brønsted acid mediated reactions of MCPs with acetonitrile

N‑Heterocyclic Carbene–Palladium(II)–4,5-Dihydrooxazole Complexes: Synthesis and Catalytic Activity toward Amination of Aryl Chlorides

A series of novel N-heterocyclic carbene–palladium­(II)–4,5-dihydrooxazole (NHC-Pd^II-Ox) complexes <b>3</b> were successfully synthesized from commercially available imidazolium salts <b>1</b>, PdCl₂, and 4,5-dihydrooxazoles <b>2</b> in a one-step process, and these complexes showed efficient catalytic activity toward the amination of aryl chlorides. Both secondary and primary amines were tolerated under the same reaction conditions. Under the optimal reaction conditions, the expected coupling products were obtained in moderate to high yields

Reversible Near-Infrared pH Probes Based on Benzo[<i>a</i>]phenoxazine

Several benzo­[<i>a</i>]­phenoxazine derivatives containing substituted N-aromatic groups are evaluated for their pH-dependent absorption and emission properties. Among the compounds exhibiting optical responses under near-neutral and subacid pH conditions, benzo­[<i>a</i>]­phenoxazine derivatives with an electron-withdrawing aromatic group attached to nitrogen of the imino group show potential application as near-infrared pH sensors. Three water-soluble pH probes based on benzo­[<i>a</i>]­phenoxazine with different pyridinium structures are designed and synthesized. Their reversible pH-dependent emissions in buffer solution containing 0.1% dimethyl sulfoxide (DMSO) locate in 625–850 nm with the fluorescent enhancement of 8.2–40.1 times, and their calculated p<i>K</i>_a values are 2.7, 5.8, and 7.1, respectively. A composite probe containing the three benzo­[<i>a</i>]­phenoxazines shows a linear pH–emission relationship in the range of pH 1.9–8.0. Real-time detection of intracellular pH using an in vitro assay with HeLa cells is also reported

Synthesis, Characterization, and Nonvolatile Ternary Memory Behavior of a Larger Heteroacene with Nine Linearly Fused Rings and Two Different Heteroatoms

To achieve ultrahigh density memory devices with the capacity of 3ⁿ or larger, organic materials with multilevel stable states are highly desirable. Here, we reported a novel larger stable heteroacene, 2,3,13,14-tetradecyloxy-5,11,16,22-tetraaza-6,10,17,21-tetrachloro-7,9,18,20-tetraoxa-8,19-dicyanoenneacene (CDPzN), which has two different types of heteroatoms (O and N) and nine linearly fused rings. The sandwich-structure memory devices based on CDPzN exhibited excellent ternary memory behaviors with high ON2/ON1/OFF current ratios of 10^6.3/10^4.3/1 and good stability for these three states

Synthesis, Physical Properties, and Light-Emitting Diode Performance of Phenazine-Based Derivatives with Three, Five, and Nine Fused Six-Membered Rings

Realizing the control of emission colors of single molecules is very important in the development of full-color emitting materials. Herein, three novel phenazine derivatives (2,3,7,8-tetrakis­(decyloxy)­phenazine (<b>2a</b>), 2,3-didecyloxy-5,14-diaza-7,12-dioxo-9,10- dicyanopentacene (<b>2b</b>), and 2,3,13,14-tetradecyloxy-5,11,16,22-tetraaza-7,9,18,20-tetraoxo-8,19-dicyanoenneacene (<b>2c</b>)) have been successfully synthesized and fully characterized. Compound <b>2c</b> can emit blue light in toluene solution (450 nm), green light in the powder/film state (502/562 nm), and red light in the <b>2c</b>/TFA state (610 nm). The OLED with <b>2c</b> emits a strong green light at a peak of 536 nm with a maximum luminance of the OLED of about 8600 cd m^–2, which indicates that <b>2c</b> could be a promising fluorescent dye for OLED applications

Poly(3,4-ethylenedioxythiophene)–Poly(styrenesulfonate) Interlayer Insertion Enables Organic Quaternary Memory

Herein, for the first time, quaternary resistive memory based on an organic molecule is achieved via surface engineering. A layer of poly­(3,4-ethylenedioxythiophene)–poly­(styrenesulfonate) (PEDOT–PSS) was inserted between the indium tin oxide (ITO) electrode and the organic layer (squaraine, SA-Bu) to form an ITO/PEDOT–PSS/SA-Bu/Al architecture. The modified resistive random-access memory (RRAM) devices achieve quaternary memory switching with the highest yield (∼41%) to date. Surface morphology, crystallinity, and mosaicity of the deposited organic grains are greatly improved after insertion of a PEDOT–PSS interlayer, which provides better contacts at the grain boundaries as well as the electrode/active layer interface. The PEDOT–PSS interlayer also reduces the hole injection barrier from the electrode to the active layer. Thus, the threshold voltage of each switching is greatly reduced, allowing for more quaternary switching in a certain voltage window. Our results provide a simple yet powerful strategy as an alternative to molecular design to achieve organic quaternary resistive memory