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