Ruthenium-catalyzed cascade C-H activation/annulation of N-alkoxybenzamides : reaction development and mechanistic insight

A highly selective ruthenium-catalyzed C-H activation/annulation of alkyne-tethered N-alkoxybenzamides has been developed. In this reaction, diverse products from inverse annulation can be obtained in moderate to good yields with high functional group compatibility. Insightful experimental and theoretical studies indicate that the reaction to the inverse annulation follows the Ru(ii)-Ru(iv)-Ru(ii) pathway involving N-O bond cleavage prior to alkyne insertion. This is highly different compared to the conventional mechanism of transition metal-catalyzed C-H activation/annulation with alkynes, involving alkyne insertion prior to N-O bond cleavage. Via this pathway, the in situ generated acetic acid from the N-H/C-H activation step facilitates the N-O bond cleavage to give the Ru-nitrene species. Besides the conventional mechanism forming the products via standard annulation, an alternative and novel Ru(ii)-Ru(iv)-Ru(ii) mechanism featuring N-O cleavage preceding alkyne insertion has been proposed, affording a new understanding of transition metal-catalyzed C-H activation/annulation

Synthesis of Pyrrolo[1,2-b]isoquinolines via Gold(I)-Catalyzed Cyclization/Enyne Cycloisomerization/1,2-Migration Cascade

A gold(I)-catalyzed cascade transformation of N-alkynic 2-ynamides for the rapid and efficient synthesis of the indolizidine scaffold is developed. Through a sequential nucleophilic cyclization/enyne cycloisomerization/1,2-migration process, diverse pyrrolo[1,2-b]isoquinolines are obtained under mild conditions in a regiospecific and convergent manner. Various alkyl and aryl migrating groups are tolerated in this process. The electronic effect of the migrating group is comprehensively investigated. The study of the mechanism indicates that the pathway involving a gold carbenoid species is the main pathway and that the 1,2-migration of alkyl and aryl groups to the gold carbenoid occurs in an intramolecular fashion. This cascade reaction is also employed as the key step for the synthesis of a decumbenine B analogue.status: publishe

Efficient synthesis of the indoloazocine framework via intramolecular alkyne carbocyclization

A microwave-assisted protocol based on an Hg(OTf)(2) catalyzed intramolecular alkyne carbocyclization reaction was developed for selective construction of the indoloazocine core

Cationic Gold(I)-Catalyzed Cascade Bicyclizations for Divergent Synthesis of (Spiro)polyheterocycles

© 2018 American Chemical Society. We herein report an expeditious synthetic strategy to access diverse (spiro)polyheterocycles from easily available starting materials in two operational steps including an Ugi four-component reaction and a cationic gold(I)-catalyzed cascade bicyclization. Divergent synthesis of these structurally complex pyrido[2,1-a]isoindol-4(6H)-ones and spiroisoquinoline-pyrrole-3,5′-diones via a cascade nucleophilic cyclization/intramolecular 1,3-migration/1,5-enyne cycloisomerization process and a tandem hydroamination/Michael addition sequence, respectively, was controlled by substituents, where the electronic effect on the migrating groups and steric effect of the secondary amide moieties play crucial roles.status: publishe

Diversification of Peptidomimetics and Oligopeptides through Microwave-Assisted Rhodium(III)-Catalyzed Intramolecular Annulation

status: publishe