Rh-catalyzed chemo-, stereo- and regioselective C-H cascade annulation of indolyloxopropanenitriles for pyranoindoles

Selective annulations of alkynes represent a powerful tool for constructing multicyclic scaffolds while installing desired substitution patterns with precision. Herein, we report a Rh-catalyzed unique annulation of indolyl oxopropanenitrile with hydroxy-alkynoates to access pyranoindole cyclic motifs, featuring enol oxygen as a rare chemoselective reactive terminal. The reaction proceeds via a five-membered oxy-rodacycle through C-H activation by a rhodium complex guided by enolic- and propargyloxy dual co-ordination to enable a regio- and stereoselective modular assembly.

Rhodium-Catalyzed Regioselective Double Annulation of Enaminones with Propargyl Alcohols: Rapid Access to Arylnapthalene Lignan Derivatives

We present here a rhodium-catalyzed oxidative three-point double annulation of enaminones with propargylic alcohols via a C-H and a C-N bond activation to access arylnaphthalene-based lignan derivatives. The key step in the reaction is the regioselective insertion of propargylic alcohol into the rhoda-cycle, a result of hydroxyl rhodium coordination. Necessary control experiments and KIE studies were conducted to determine the mechanism.

Rhodium-Catalyzed Annulation of Phenacyl Ammonium Salts with Propargylic Alcohols via a Sequential Dual C-H and a C-C Bond Activation: Modular Entry to Diverse Isochromenones

Given their omnipresence in natural products and pharmaceuticals, isochromenone congeners are one of the most privileged scaffolds to synthetic chemists. Disclosed herein is a dual (ortho/meta) C-H and C-C activation of phenacyl ammonium salts (acylammonium as traceless directing group) toward annulation with propargylic alcohols to accomplish rapid access for novel isochromenones by means of rhodium catalysis from readily available starting materials. This operationally simple protocol features broad substrate scope and wide functional group tolerance. Importantly, the protocol circumvents the need of any stoichiometric metal oxidants and proceeds under aerobic conditions.

Regioselective benzannulation of allylic sulfur ylides with ynones: a rapid access to substituted thioanisoles

The efficiency and selectivity of annulation reactions are often difficult to control in the presence of multiple potential reactive centers, like in the case of allylic sulfur ylides (ASY). Here, we describe a novel base mediated [3+3] benzannulation of ASY and readily available alkynones, which accomplishes the regioselective formation of multisubstituted thioanisoles, highly sought after chemical scaffolds. A new reactivity pattern of ASY has been unearthed, where it acted as both a 3C component and sulfur source in benzannulation. Use of a widely available base, operational simplicity and broad substrate scope are the additional salient features of the conversion.

Base-Mediated Cyclopentannulation of Ynones with Amino Crotonates for Regio- and Stereoselective Synthesis of Pentafulvenes and Cyclopenta[c]quinolines

A regio- and stereoselective synthesis of unsymmetrically substituted pentafulvenes is reported via the condensation of readily available ynones and amino crotonates under very mild conditions. The mechanism of this 3 + 2 annulation involved a vinylogous Michael addition followed by an intramolecular enamine aldol condensation. Substrates with o-bromo tether further cyclized to pentannulated hydroquinolines through an isomerization/S_NAr in the same reaction pot at the elevated temperature.

Synthesis of isoquinolones by visible-light-induced deaminative [4+2] annulation reactions

A metal-free approach for the synthesis of isoquinolone derivatives by means of photoinitiated deaminative [4+2] annulation of alkynes and N-amidepyridinium salts is presented.