Diastereoselective Construction of Structurally Diverse 2,3-Dihydro-quinolin-4-one scaffolds via Redox Neutral Cascade [1,7]-Hydride Transfer/Cyclization

The pharmaceutically significant 2,3-dihydroquinolin-4-one scaffolds were constructed diastereoselectively and facilely via redox-neutral cascade Knoevengel condensation/[1,7]-hydride transfer/cyclization/transesterification in DCE from readily available methyl 2-aminobenzoacetate and diverse aldehydes, which features novel &...

Borane-Catalyzed Cascade Friedel-Crafts Alkylation/[1,5]-Hydride Transfer/Mannich Cyclization to Afford Tetrahydroquinolines

An unprecedented redox-neutral annulation of tertiary anilines with electron-deficient alkynes was developed that proceeds through a cascade Friedel-Crafts alkylation/[1,5]-hydride transfer/Mannich cyclization sequence. Under B(C6F5)3 catalysis, a range of functionalized 1,2,3,4-tetrahydroquinolines...

Intermolecular Diastereoselective Annulation of Azaarenes into Fused N-heterocycles by Ru(II) Reductive Catalysis

Despite the important advances in azaaryl C−H activation/functionalization, reductive functionalization of ubiquitously distributed but weakly reactive azaarenes remains to date a challenge. Herein, by a strategy incorporating a tandem coupling sequence into the reduction of azaarenes, we present a dearomative annulation of azaarenes into promising fused syn-N-heterocycles by combination with a large variety of aniline derivatives and paraformaldehyde under ruthenium(II) reductive catalysis, proceeding with excellent selectivity, mild conditions, and broad substrate and functional group compatibility. Mechanistic studies reveal that the products are formed via hydride transfer-initiated β-aminomethylation and α-arylation of the pyridyl core in azaarenes, paraformaldehyde serves as both the C1-building block and reductant precursor, and the use of Mg(OMe)2 base plays a critical role in determining the reaction chemo-selectivity by lowering the hydrogen transfer rate. The present work opens a door to further develop valuable reductive functionalization of unsaturated systems by taking profit of formaldehyde-endowed two functions.

Hydrogenation of Olefins, Alkynes, Allenes, and Arenes by Borane-based Frustrated Lewis Pairs

In recent years, borane-based frustrated Lewis pairs proved to be efficient hydrogenation catalysts and became an alternative to transition metal-based systems. The hydrogen activation by classic FLPs leads to a protonated Lewis base and a borohydride. Consequently, hydrogenations catalyzed by classic FLPs consist of stepwise hydride transfer reactions and protonations (or vice versa). More recently, systems that operate via an initial hydroboration have allowed extending the substrate scope for FLP catalyzed hydrogenations. Within this review, hydrogenations of organic substrates catalyzed by borane-based frustrated Lewis pairs are discussed. Emphasis is given to the mechanistic aspects of these catalytic reactions.