Direct Catalytic Asymmetric Mannich‐Type Reaction of Thioamides

Taking the reins : The title transformation of thioamides and N‐diphenylphosphinoyl imines is described. By harnessing the power of cooperative catalysis between a soft Lewis acid and a hard Brønsted base, thioamide carbon pronucleophiles can furnish Mannich products (see scheme). Divergent transformation of the thioamide functionality highlights the utility of this methodology.

     

An Ultrastable,Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face-centered-cubic-type small {Ag₇}⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃W₂₇O₉₆]¹⁸⁻. The cluster showed unique {Ag₇}⁵⁺-to-POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇}⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂, water, and solvents.     

Simultaneous Spin-Crossover Transition and Conductivity Switching in a Dinuclear Iron(II) Coordination Compound Based on 7,7′,8,8′-Tetracyano-p-quinodimethane

The reaction of Fe(OAc)₂ and Hbpypz with neutral TCNQ results in the formation of [Fe₂(bpypz)₂(TCNQ)₂](TCNQ)₂ ( 1 ), in which Hbpypz=3,5-bis(2-pyridyl)pyrazole and TCNQ=7,7′,8,8′-tetracyano-p-quinodimethane. Crystal packing of 1 with uncoordinated TCNQ and π–π stacking of bpypz⁻ ligands produces an extended two-dimensional supramolecular coordination assembly. Temperature dependence of the dc magnetic susceptibility and heat capacity measurements indicate that 1 undergoes an abrupt spin crossover (SCO) with thermal spin transition temperatures of 339 and 337 K for the heating and cooling modes, respectively, resulting in a thermal hysteresis of 2 K. Remarkably, the temperature dependence of dc electrical transport exhibits a transition that coincides with thermal SCO, demonstrating the thermally induced magnetic and electrical bistability of 1 , strongly correlating magnetism with electrical conductivity. This outstanding feature leads to thermally induced simultaneous switching of magnetism and electrical conductivity and a magnetoresistance effect.     

Fluorescent Short-Stranded Helical Foldamers Based on L-shaped Dibenzopyrrolo[1,2-a][1,8]naphthyridine

Helical structures were constructed by using π-spacer-bridged dimers of dibenzopyrrolo[1,2-a][1,8]naphthyridine, which has a highly fluorescent L-shaped π-extended skeleton. Three dimers with biphenylene (dimer 1 ), phenanthrene (dimer 2 ), and m-phenylene (dimer 3 ) spacers, as well as a fixed-helical dimer 4 where two quinolone rings were covalently cross-linked, were designed and prepared. ¹H NMR and ROESY spectra revealed that dimers 1 and 2 adopted helical forms in solution, whereas dimer 3 did not. The helical conformation of 1 was strengthened by addition of either polar or nonpolar solvents to the chloroform solution, which suggested that π–π stacking was the main contributor to the stabilization of the helical structure. All of the dimers, including fixed-helical dimer 4 , emitted fluorescence with high quantum yields (ϕ=0.79–0.86).     

Highly Chemoselective gem-Difluoropropargylation of Aliphatic Alcohols

Despite the potential of α-fluoroethers in medicinal chemistry, their synthetic methods, especially etherification of aliphatic alcohols, have been limited. Herein, we developed two- and three-step gem-difluoropropargylation of aliphatic alcohols including amino acid derivatives and naturally occurring bioactive molecules. Highly chemoselective etherification proceeded by using the gem-difluoropropargyl bromide dicobalt complex in the presence of silver triflate and triethylamine. Decomplexation of dicobalt complexes was achieved by using cerium ammonium nitrate or N,N,N′-trimethylethylenediamine. The thus obtained gem-difluoropropargyl ethers were converted to various α-difluoroethers which are expected to be useful for medicinal chemistry.     

Polymeric Design for Electron Transfer in Photoinduced Hydrogen Generation through a Coil–Globule Transition

To realize a renewable energy society, a polymeric system for photoinduced hydrogen generation utilizing a copolymer containing an electron acceptor was designed. In this system, the redox changes of viologen introduced into poly(N‐isopropylacrylamide) cause cyclic conformational changes owing to the shifting of the phase transition temperature (PTT). The polymeric coil–globule transitions with hydrophilic/hydrophobic changes accelerate the electron transfer for hydrogen generation. In particular, hydrogen generation using visible‐light energy with high efficiency is achieved around the PTT. In contrast to conventional solution systems, our polymeric system enables efficient hydrogen generation in a close molecular arrangement without the aggregation of catalytic nanoparticles. The utilization of conformational changes will provide a new strategy for synthesizing artificial photosynthetic hydrogels that split water to generate both hydrogen and oxygen.     

Conquering amide planarity: Structural distortion and its hidden reactivity

Amides are generally considered as a low-reactive chemical entity among the carbonyl group, and therefore fewer opportunities to be involved in catalytic transformations as substrates. The origin of the stable nature of amides is resonance stabilization in the planar structure, which has drawn considerable attention from organic and physical chemists, leading to the discovery of distorted amides that exhibit a substantially reactive nature. Recent focus in this field is on the catalytic transformation of designed amides with moderate distortion or reduced resonance stabilization. This digest reviews the brief history of the quest for highly distorted amides and introduces a collection of recent studies on catalytic transformations of designed amides.