Copper-Catalyzed Aza-Michael Addition of 2‑Aminobenzoate to β‑Substituted α,β-Unsaturated Ketones: One-Pot Synthesis of 3‑Carbonyl-2-Substituted Quinolin-4(1<i>H</i>)‑ones

We present a new and straightforward one-pot process for the synthesis of 3-carbonyl-4-quinolone derivatives through highly efficient Cu-catalyzed aza-Michael addition of 2-aminobenzoates to β-substituted α,β-unsaturated ketones/cyclization/mild oxidation reactions. A broad range of new versatile 3-carbonyl-quinolin-4­(1<i>H</i>)-ones is prepared from readily available chemicals under mild reaction conditions with short reaction times, producing good to excellent yields (up to 99%)

Torsionally Responsive Tropone-Fused Conjugated Polymers

Torsionally responsive molecular systems can change their electronic properties according to the dihedral angles and can be utilized as sensory materials. We have designed and synthesized novel tropone-fused conjugated polymers <b>PBTr</b>, <b>PBTr-T</b>, and <b>PBTr-Tz</b> that showed interesting dihedral-angle-dependent variations in UV–vis absorptions. Tropone-fused thiophene derivatives were prepared from one-step condensation of thiophene-3,4-dialdehyde and aliphatic ketones via a modular, facile, and high-yielding method. Subsequent halogenation and Stille cross-coupling polymerization with a bis­(stannyl)­benzo­dithiophene resulted in a tropone-fused conjugated polymer <b>PBTr</b>. We were also able to prepare thiophene- and thiazole-bridged polymers, <b>PBTr-T</b> and <b>PBTr-Tz</b>, respectively, using similar synthetic methods. Electronic absorptions of the newly synthesized <b>PBTrs</b> were measured in solutions and in films states. Substantial red-shifts occurred in the case of thiophene-bridged <b>PBTr-T</b>, whereas almost no shift was observed for thiazole-bridged <b>PBTr-Tz</b>. We attributed this to the substantial change in the torsional angle between the tropone-fused thiophene moiety and thiophene, which was further supported by density functional theory (DFT) calculations. Similar spectral changes of UV–vis absorptions were observed when a poor solvent (methanol) was introduced to a chloroform solution of <b>PBTr-T</b>. Reverse torsional angle variations were realized with initially planar <b>PBTr-Tz</b> by introducing steric hindrance through protonation on the thiazole rings. We believe that torsionally responsive tropone-fused conjugated polymers are promising as novel platforms for sensory applications

Structural Effect of Thioureas on the Detection of Chemical Warfare Agent Simulants

The ability to rapidly detect, identify, and monitor chemical warfare agents (CWAs) is imperative for both military and civilian defense. Since most CWAs and their simulants have an organophosphonate group, which is a hydrogen (H)-bond acceptor, many H-bond donors have been developed to effectively bind to the organophosphonate group. Although thioureas have been actively studied as an organocatalyst, they are relatively less investigated in CWA detection. In addition, there is a lack of studies on the structure–property relationship for gas phase detection. In this study, we synthesized various thioureas of different chemical structures, and tested them for sensing dimethylmethylphosphonate (DMMP), a CWA simulant. Molecular interaction between DMMP and thiourea was measured by ¹H NMR titration and supported by density functional theory (DFT) calculations. Strong H-bond donor ability of thiourea may cause self-aggregation, and CH−π interaction can play an important role in the DMMP detection. Gas-phase adsorption of DMMP was also measured using a quartz crystal microbalance (QCM) and analyzed using the simple Langmuir isotherm, showing the importance of structure-induced morphology of thioureas on the surface

Topologically Reversible Transformation of Tricyclic Polymer into Polyring Using Disulfide/Thiol Redox Chemistry

A polyring capable of reversible growth and dissociation is synthesized from a tricyclic polystyrene (PS) prepared by combining atom transfer radical polymerization of a 4-arm star-shaped PS and azide–alkyne click reactions. In the preparation of the tricyclic PS, a coupling agent containing a disulfide linkage is used in the click cyclization reaction. The reduction of the disulfide linkage in the tricyclic PS results in an 8-shaped PS with thiol groups which on oxidation leads to a high molecular weight polyring. The topology transformation between the polymers occurs via reversible redox reaction of disulfide/thiol. The high molecular weight of the polyring is realized due to the formation of flexible S–S linkage between the 8-shaped PSs. Their structures are confirmed by FT-IR, ¹H NMR, SEC, and MALDI-TOF MS analyses. In addition, molecular weight control of the polyring according to polymer concentration has been confirmed through SEC analysis