N,O-aminals, molecules bearing a geminally N,O-substituted (stereogenic) carbon center, have been recently recognized as an important class of building blocks in organic synthesis. As direct precursors of imines and iminium ions, N,O-aminals were converted through asymmetric organocatalysis or metal catalysis to diverse enantiomerically enriched compounds including N-heterocycles. Furthermore, cyclic N,O-hemiaminals acted as acyclic amino aldehyde surrogates, which were transformed to enantioenriched products otherwise challenging to access. Finally, cyclic N,O-aminals were formed in situ as key intermediates in asymmetric catalysis. In this review, we introduce a wide array of catalytic asymmetric protocols involving the use of four distinct types of N,O-aminals as starting materials or key intermediates.

[reaction: see text] Phosphine dendrimer-stabilized palladium nanoparticles were synthesized and found to be highly effective for Suzuki coupling reactions, affording good to excellent product yields, high turnover number (up to 65,000), and excellent reusability (up to 9 catalytic runs). Furthermore, these Pd nanoparticles are efficient and selective catalysts for hydrogenations.

Given the important agricultural and medicinal application of optically pure heterocycles bearing a trifluoromethyl group at the stereogenic carbon center in the heterocyclic framework, the exploration of efficient and practical synthetic strategies to such types of molecules remains highly desirable. Catalytic enantioselective synthesis has one clear advantage that it is more cost-effective than other synthetic methods, but remains limited by challenges in achieving excellent yield and stereoselectivities with a low catalyst loading. Thus far, numerous models of organo- and organometal-catalyzed asymmetric reactions have been exploited to achieve this elusive goal over the past decade. This review article describes recent progress on this research topic, and focuses on an understanding of the catalytic asymmetric protocols exemplified in the catalytic enantioselective synthesis of a wide range of complex enantioenriched trifluoromethylated heterocycles.

Aminal attraction: The combination of indium(I) chloride and a chiral silver binol phosphate provides an excellent catalyst for asymmetric Hosomi–Sakurai reactions between N,O‐aminals and boronates (see scheme; PG=protecting group, pin=pinacolato). The substrate scope includes aromatic, heteroaromatic, and aliphatic N,O‐aminals as well as allyl and allenyl boronates.

Chiral nonracemic guanidines act as Brønsted bases to generate guanidinium enolates for the enantioselective electrophilic trifluoromethylation of beta-keto esters by means of S-(trifluoromethyl)dibenzothiophenium tetrafluoroborate (Umemoto reagent) with good enantioselectivity of 60-70% range. Despite the fact that the ees are still improvable, the model reported in this work could spark the imagination of chemists to design new chiral bases to improve the stereochemical outcome.

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Air-and light-stable electrophilic difluoromethylating reagents, S-(difluoromethyl)-S-phenyl-S-(2,4,6-trialkoxyphenyl) sulfonium salts were successfully developed, and the introduction of intramolecular hydrogen bonds plays a crucial role for the stabilities and reactivities of these reagents. C-selective difluoromethylation of a broad range of β-ketoesters and malonates proceeded smoothly under mild reaction conditions to give good to excellent yields with excellent C/O regioselectivities.

This paper investigates the fluidic leak rate through metal sealing surfaces by developing fractal models for the contact process and leakage process. An improved model is established to describe the seal-contact interface of two metal rough surface. The contact model divides the deformed regions by classifying the asperities of different characteristic lengths into the elastic, elastic-plastic and plastic regimes. Using the improved contact model, the leakage channel under the contact surface is mathematically modeled based on the fractal theory. The leakage model obtains the leak rate using the fluid transport theory in porous media, considering that the pores-forming percolation channels can be treated as a combination of filled tortuous capillaries. The effects of fractal structure, surface material and gasket size on the contact process and leakage process are analyzed through numerical simulations for sealed ring gaskets.