Stereoselective Sequential [4+2]/[2+2] Cycloadditions Involving 2-Alkenylindolenines: An Approach to Densely Functionalized Benzo[ b]indolizidines.

A stereoselective sequential [4+2]/[2+2] cycloaddition process involving 2-alkenylindolenines has been developed. This unprecedented protocol allows a rapid access to densely functionalized benzo[ b]indolizidines containing a fully substituted piperidine ring with five contiguous stereogenic centers in good yields with excellent diastereoselectivities. This finding demonstrated the unique synthetic utility of the 2-alkenylindolenine species in the construction of complex polycyclic N-heterocycles.

Asymmetric [3+2] cycloaddition of 3-amino oxindole-based azomethine ylides with α,ß-ynones: a straightforward approach to spirooxindoles incorporating 2,5-dihydropyrroles and pyrroles.

An organocatalytic asymmetric [3+2] cycloaddition of 3-amino oxindole-based azomethine ylides and α,ß-ynones has been developed. This reaction afforded spiro[dihydropyrrole-2,3'-oxindole] products in high chemical yields with excellent stereoselectivities (up to 99% yields, >20 : 1 dr and >99% ee). Notably, a series of important spiro[pyrrole-oxindole] derivatives were readily obtained via oxidation of the cycloadducts, thus extending the diversity of the products.

An Organocatalytic Asymmetric Friedel-Crafts Addition/Fluorination Sequence: Construction of Oxindole-Pyrazolone Conjugates Bearing Vicinal Tetrasubstituted Stereocenters.

A highly efficient and practical one-pot sequential process, consisting of an organocatalytic enantioselective Friedel-Crafts-type addition of 4-nonsubstituted pyrazolones to isatin-derived N-Boc ketimines and a subsequent diastereoselective fluorination of the pyrazolone moiety, is developed. This reaction sequence delivers novel oxindole-pyrazolone adducts featuring vicinal tetrasubstituted stereocenters with a 0.5 mol % catalyst loading in high yield with excellent enantio- and diastereocontrol. Notably, chloro, bromo, and thioether functionalities can be readily incorporated, rendering a broad diversity of the product.

Organocatalytic enantioselective α-amination of 5-substituted rhodanines: an efficient approach to chiral N,S-acetals.

We report a highly efficient approach to constructing chiral N,S-acetals using 5-substituted rhodanines as sulfur-bound pronucleophiles catalyzed by natural cinchona alkaloids quinine or quinidine. This α-amination reaction has a broad substrate scope, and the products featuring both rhodanine and N,S-acetal structural motifs were obtained in high yields and excellent enantioselectivities.

Toward low friction in high vacuum for hydrogenated diamondlike carbon by tailoring sliding interface.

The high friction of diamondlike carbon (DLC) films in vacuum impedes achieving their application in space environment. Here we show that the vacuum friction coefficients can be lowered below 0.1 by avoiding formation of carbonaceous transfer layers on the counterfaces. First-principles calculations reveal that the low friction coefficients stem from intrinsically weak-interacting sliding interfaces. Conversely, formation of transfer layers and carbonaceous sliding interfaces thus established are invalid for friction reduction for DLC in vacuum. The mating materials are thus highlighted for their crucial roles in transfer-layer formation.