In this study, the design and asymmetric synthesis of a series of chiral targets of orientational chirality were conducted by taking advantage of
-sulfinylimine-assisted nucleophilic addition and ...modified Sonogashira catalytic coupling systems. Orientational isomers were controlled completely using alkynyl/alkynyl levers C(sp)-C(sp) axis with absolute configuration assignment determined by X-ray structural analysis. The key structural element of the resulting orientational chirality is uniquely characterized by remote through-space blocking. Forty examples of multi-step synthesis were performed, with modest to good yields and excellent orientational selectivity. Several chiral orientational amino targets are attached with scaffolds of natural and medicinal products, showing potential pharmaceutical and medical applications in the future.
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A new chiral aggregate-based tool for asymmetric synthesis has been developed by taking advantage of chiral aggregates of GAP (Group-Assisted Purification) reagents,
N
-phosphonyl imines. This tool ...was proven to be successful in the asymmetric GAP synthesis of functionalized 2,3-dihydrobenzofurans by reacting salicyl
N
-phosphonyl imines with dialkyl bromomalonates in various cosolvent systems. The chiral induction can be controlled by differentiating between two asymmetric directions simply by changing the ratios of cosolvents which are commonly adopted in AIE (aggregation-induced emission) systems. The formation of chiral aggregates was witnessed by a new analytical tool—aggregation-induced polarization (AIP). The present synthetic method will be broadly extended for general organic synthesis, particularly, for asymmetric synthesis and asymmetric catalysis in the future.
The phenomenon of aggregation-induced polarization (AIP) was observed showing optical rotation amplification and adjustment. The relationship between optical rotations of chiral aggregates of ...multilayered chiral folding oligomers and polymers with water% in THF (
f
w
) has been established accordingly. New multilayered chiral oligomers were synthesized under the asymmetric catalytic systems established by our laboratory recently. These products were well-characterized by UV-vis, NMR, and MALDI-TOF spectra. Absolute stereochemistry (enantio- and diastereochemistry) was assigned by comparison with similar asymmetric induction by the same catalyst in our previous reactions. The present AIP work can serve as a new tool to determine chiral aggregates, especially for those that cannot display emission. AIP would also complement AIE-based CPL since AIP serves as a new tool providing enhanced right- or left-hand polarized lights with individual wavelengths. It will find many applications in chemical and materials science in the future.
A new type of chirality, orientational chirality, consisting of a tetrahedron center and a remotely anchored blocker, has been discovered. The key structural element of this chirality is ...characterized by multiple orientations directed by a through-space functional group. The multi-step synthesis of orientational chiral targets was conducted by taking advantage of asymmetric nucleophilic addition, Suzuki-Miyaura cross-coupling and Sonogashira coupling. An unprecedented catalytic species showing a five-membered ring consisting of C (sp
)-Br-Pd-C (sp
) bonds was isolated during performing Suzuki-Miyaura cross-coupling. X-ray diffraction analysis confirmed the species structure and absolute configuration of chiral orientation products. Based on X-ray structures, a model was proposed for the new chirality phenomenon to differentiate the present molecular framework from previous others. DFT computational study presented the relative stability of individual orientatiomers. This discovery would be anticipated to result in a new stereochemistry branch and to have a broad impact on chemical, biomedical, and material sciences in the future.
New multilayer 3D chiral molecules have been designed and synthesized asymmetrically through the strategy of center-to-multilayer folding chirality control and double Suzuki couplings. Individual ...diastereoisomers were readily obtained and separated
flash column chromatography. The key diastereoisomer was further converted into corresponding enantiomers. These enantiomers possess electron-deficient aromatic bridges layered with top and bottom aromatic scaffolds. X-ray structural analysis has unambiguously confirmed the configuration, and intermolecular packing results in regular planar patterns in solid crystals. The synthesis was achieved in a total of ten steps starting from commercially available starting materials.
A novel class of polymers and oligomers of chiral folding chirality has been designed and synthesized, showing structurally compacted triple-column/multiple-layer frameworks. Both uniformed and ...differentiated aromatic chromophoric units were successfully constructed between naphthyl piers of this framework. Screening monomers, catalysts, and catalytic systems led to the success of asymmetric catalytic Suzuki-Miyaura polycouplings. Enantio- and diastereochemistry were unambiguously determined by X-ray structural analysis and concurrently by comparison with a similar asymmetric induction by the same catalyst in the asymmetric synthesis of a chiral three-layered product. The resulting chiral polymers exhibit intense fluorescence activity in a solid form and solution under specific wavelength irradiation.
So far, there have been 4 methods to control chirality including the use of chiral auxiliaries, reagents, solvents, and catalysts documented in literature and textbooks. Among them, asymmetric ...catalysts are normally divided into homogeneous and heterogeneous catalysis. In this report, we present a new type of asymmetric control-asymmetric catalysis via chiral aggregates that would not belong to the above categories. This new strategy is represented by catalytic asymmetric dihydroxylation reaction of olefins in which chiral ligands are aggregated by taking advantage of typical aggregation-induced emission systems containing tetrahydrofuran and H
O cosolvents. It was proven that the chiral induction can be enhanced from er of 78:22 to 97:3 simply by changing the ratios of these 2 cosolvents. The formation of chiral aggregates of asymmetric dihydroxylation ligands, (DHQD)
PHAL and (DHQ)
PHAL, has been proven by aggregation-induced emission and a new analytical tool-aggregation-induced polarization established by our laboratory. In the meanwhile, chiral aggregates were found to be formed either by adding NaCl into tetrahydrofuran/H
O systems or by increasing concentrations of chiral ligands. The present strategy also showed promising reverse control of enantioselectivity in the Diels-Alder reaction. This work is anticipated to be extended broadly to general catalysis, especially to asymmetric catalysis in the future.
Conjugated polymers and oligomers have great potentials in various fields, especially in materials and biological sciences because of their intriguing electronic and optoelectronic properties. In ...recent years, the through-space conjugation system has emerged as a new assembled pattern of multidimensional polymers. Here, a novel series of structurally condensed multicolumn/multilayer 3D polymers and oligomers have been designed and synthesized through one-pot Suzuki polycondensation (SPC). The intramolecularly stacked arrangement of polymers can be supported by either X-ray structural analysis or computational analysis. In all cases, polymers were obtained with modest to good yields, as determined by GPC and
H-NMR. MALDI-TOF analysis has proven the speculation of the step-growth process of this polymerization. The computational study of ab initio and DFT calculations based on trimer and pentamer models gives details of the structures and the electronic transition. Experimental results of optical and AIE research confirmed by calculation indicates that the present work would facilitate the research and applications in materials.
Orientational chirality was discovered and characterized by a C(sp)–C(sp
3
) axis-anchored chiral center and a remotely anchored blocker. X-ray structural analysis proved that orientatiomers are ...stabilized by through-space functional groups, making it possible for 1
R
- or
S
-chiral center to exhibit 3 orientational isomers simply by rotating operations. A new model system was proposed, fundamentally different from the traditional Felkin–Ahn-type or Cram-type models. In these traditional models, chiral C(sp
3
) center and blocking C(sp
2
) carbons are connected adjacently, and there exist 6 energy barriers during rotating along the C(sp
2
)−C(sp
3
) axis. In comparison, the present orientational chirality model shows that a chiral C(sp)–C(sp
3
) carbon is remotely located from a blocking group. Thus, it is focused on the steric dialog between a chiral C(sp
3
) center and a remotely anchored functional group. There exist 3 energy barriers for either (
R
)– or (
S
)–C(sp)–C(sp
3
) stereogenicity in the new model. Chiral amide auxiliary was proven to be an excellent chiral auxiliary in controlling rotations of orientatiomers to give complete stereoselectivity. The asymmetric synthesis of individual orientatiomers was conducted via multistep synthesis by taking advantage of the Suzuki–Miyaura cross-coupling and Sonogashira coupling reactions. Density functional theory computational study presented optimized conformers and relative energies for individual orientatiomers. This discovery would be anticipated to result in a new stereochemistry topic and have a broad impact on chemical, biomedical, and material sciences in the future.
A transition metal-free cross-dehydrogenative coupling of coumarins with acetonitrile or acetone has been established. A series of coumarins were subjected to reaction with acetonitrile or acetone in ...the presence of tert-butyl benzoperoxoate and potassium fluoride for direct synthesis of 3-cyanomethyl (or acetomethyl) coumarins. The method exhibits good functional group tolerance, and desired products were obtained in moderate to good yields. Meanwhile, a radical pathway was proposed to describe the cross-dehydrogenative coupling of coumarins with acetonitrile.
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