Hydrofunctionalization, the direct addition of an X–H (e.g., X=O, N) bond across an alkene, is a desirable strategy to make heterocycles that are important structural components of naturally occurring molecules. Described here is the design and discovery of “donor–acceptor”-type platinum catalysts that are highly effective in both hydroalkoxylation and hydroamination of unactivated alkenes over a broad range of substrates under mild conditions. A number of alkene substitution patterns are accommodated, including tri-substituted, 1,1-disubstituted, (E)-disubstituted, (Z)-disubstituted and even mono-substituted double bonds. Detailed mechanistic investigations suggest a plausible pathway that includes an unexpected dissociation/re-association of the electron-deficient ligand to form an alkene-bound “donor–acceptor”-type intermediate. These mechanistic studies help understand the origins of the high reactivity exhibited by the catalytic system, and provide a foundation for the rational design of chiral catalysts towards asymmetric hydrofunctionalization reactions.
The quorum sensing (QS) system inhibitors of Pseudomonas aeruginosa are thought to attenuate bacterial pathogenicity and drug resistance by inhibiting biofilm formation and the production of virulence factors. In this study, a synthetic approach to the natural products cajaninstilbene acid (1) and amorfrutins A (2) and B (3) has been developed and was characterized by the Heck reaction, which was used to obtain the stilbene core and a Pinick oxidation to give the O-hydroxybenzoic acid. The biological activities of these compounds against the P. aeruginosa quorum sensing systems were evaluated. Amorfrutin B (3) showed promising antibiofilm activity against P. aeruginosa PAO1 with a biofilm inhibition ratio of 50.3 ± 2.7. Three lacZ reporter strains were constructed to identify the effects of compound 3 on different QS systems. Suppression efficacy of compound 3 on the expression of lasB-lacZ and pqsA-lacZ as well as on the production of their corresponding virulence factors elastase and pyocyanin was observed.
High
temperature calcined spherical alumina material with macroporous
structure is widely used in the typical strong exothermic industrial
catalytic process due to its good heat transfer ability. Aiming at
the problem that its low surface area limits the dispersion of active
metals, an in situ growth method is applied to fabricate an alumina
array on spherical alumina, while maintaining the heat transfer advantages.
Taking the as-obtained modified alumina as support, a highly dispersed
PdAg catalyst for selective hydrogenation of acetylene is synthesized,
which exhibits a remarkable enhanced intrinsic activity. Moreover,
when the conversion of acetylene reaches 90%, the selectivity toward
ethylene still remains 89%. Preferred selectivity is assigned to more
isolated Pd sites as well as high electronic density, which facilitates
the desorption of the resulting ethylene. More importantly, the array
modified catalyst exhibits good structural stability and resistance
to carbon deposition. From one aspect, the decrease of the heat production
rate over a single active site is conducive to reducing the reaction
heat accumulation, thereby avoiding the formation of hot spots over
the catalyst, which is a necessary condition for the endothermic reaction
of carbon deposition. From another point of view, both the new generated
outer opening pore structure and the original macroporous structure
of the molded alumina are beneficial for the heat transfer.
A highly enantioselective asymmetric transfer hydrogenation (ATH) of densely functionalized diheteroaryl and diaryl ketones was developed using Ru-catalysts of minimal stereogenicity. Various ketone substrates with structurally and electronically similar groups attached to the prochiral centers were reduced successfully in good to excellent enantioselectivities and yields. This protocol provides practical and efficient access to chiral diheteroarylmethanols and benzhydrols, which are key intermediates in pharmaceuticals and biologically active compounds.
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