Organic polymers and inorganic clusters belong to two different disciplines and have completely different properties and structures. When a cluster is attached to the backbone of a polymer as a pendant, the resultant hybrid polymers (polyclusters) exhibit unique behaviours totally different from those of conventional polymers owing to the nanoscale size of the cluster and its particular interactions. Herein, the aggregation of a poly(polyoxometalate)—a polynorbornene backbone with inorganic polyoxometalate cluster pendants—upon addition of a non‐solvent to its dilute solution is reported. A three‐dimensional network of tangled and snake‐like nanothreads was observed. Direct visualisation of individual nanoscale clusters enabled identification of single chains within the nanothreads. These observations suggest that during the process of aggregation, the hybrid polymer forms curved or extended chains as a consequence of an armouring effect in which the collapsed cluster pendants wrap around the backbone. The collapse occurs because they become less soluble in the solvent/non‐solvent mixture. The extended chains then become entwined and form nanoropes consisting of multiple chains wound around each other. This study provides a deeper understanding of the nature of polyclusters and should also prove useful for their future development and application.
An efficient and transition-metal-free N-arylation of amides via the insertion of arynes into the N-H bonds in the N-alkoxy amides is described. A variety of the reactive functional groups including the reactive aldehyde carbonyl group, furan ring, carbon-carbon double bonds, and free N-H bond of indole are found to be compatible with this process. In particular, the protocol is applicable in the synthesis of structurally diverse N-aryl hydroxamates and hydroxamic acids derived from N-protecting amino acids and peptides. In the presence of multiple amide N-H bonds, the N-arylation reaction can proceed selectively in the N-H bonds of terminal N-OBn amides giving rise to the desired N-aryl hydroxamates.
Palladium-catalyzed activation of remote meta-C À H bonds in arenes containing tethered alcohols was achieved with high regioselectivity by using anitrile template.Computational studies on the macrocyclic transition state of the regioselectivity-determining CÀHactivation steps revealed that both the C-N-Ag angles and gauche comformations of phenyl ether play an extremely important role in the meta selectivity.
Introduction Angelica dahurica(BZ) and Angelica dahurica var. formosana(HBZ) are two plant sources of Angelicae dahuricae Radix. Although BZ and HBZ are commonly used herbal medicines with great medicinal and dietary values, study on their phytochemicals and bioactive compositions is limited. Objective To compare the chemical compositions of BZ and HBZ and find the chemical makers for discrimination and quality evaluation of the two botanical origins of Angelicae dahuricae Radix. Methodology A high‐performance liquid chromatography coupled with quadrupole time‐of‐flight mass spectrometry method was established for chemical profiling of BZ and HBZ. Then, a quantitative analysis of multiple components by a single marker method was developed for simultaneous determination of nine bioactive coumarins (xanthotoxol, oxypeucedanin hydrate, byakangelicin, xanthotoxin, bergapten, oxypeucedanin, phellopterin, imperatorin and isoimperatorin). Moreover, chemometrics were performed to compare and discriminate BZ and HBZ samples. Results A total of 30 coumarins compounds were identified, and the chemical compositions in BZ and HBZ were quite similar. The quantitative analysis showed that there were significant differences in the contents of bioactive coumarins, and the chemometric analysis indicated five coumarins (xanthotoxol, xanthotoxin, bergapten, phellopterin and isoimperatorin) were responsible for the significant differences between BZ and HBZ, which could be used as chemical markers to distinguish the two original plant sources of Angelicae dahuricae Radix. Conclusion The present work provided useful information for understanding the chemical differences between BZ and HBZ and also provided feasible methods for quality evaluation and discrimination of herbal medicines originating from multiple botanical sources.
An intermolecular syn-1,2-arylamination of unactivated alkenes with arylboronic acids and O-benzoylhydroxylamine electrophiles has been developed with Ni(II) catalyst. The cleavable bidentate picolinamide directing group facilitated formation of stabilized 4-, 5- or 6-membered nickelacycles and enabled the difunctionalization of diverse alkenyl amines with high levels of regio-, chemo- and diastereocontrol. This general and practical protocol was compatible with broad substrate scope and high functional group tolerance. The utility of this method was further demonstrated by the site-selective late-stage modification of pharmaceutical agents.
A bidentate directing group-assisted Ni-catalyzed three component 1,2-carbosulfenylation of unactivated alkenes with aryl/alkenyloronic acids and disulfide electrophiles is reported. The reaction affords the desired products with high levels of chemo- and regioselectivity. A wide range of aryl groups and sulfur moieties can be simultaneously installed in both internal and terminal homoallylic amines with excellent functional group tolerance. Notably, the alkene substrates with a chiral center at α-position furnish α,γ-dibranched thiolamines with high diastereoselectivity and enantioselectivity that would otherwise be difficult to synthesize. The generality and scability could make this method attractive for preparing complex organosulfur compounds.
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