Multicomponent Reactions of Pyridines To Give Ring‐Fused Pyridiniums: In Situ Activation Strategy Using 1,2‐Dichloroethane as a Vinyl Equivalent

Abstract

Reported herein is a rhodium(III)‐catalyzed three‐component annulation reaction of simple pyridines, alkynes, and 1,2‐dichloroethane (DCE), affording a streamlined pathway to diverse ring‐fused pyridiniums. DCE not only serves as a vinyl equivalent but also as an in situ activating agent for pyridine C2−H activation. A cationic five‐membered rhodacycle complex has been isolated and proposed as a possible intermediate. This strategy can be extended to other N‐containing heteroarenes for the synthesis of multiring‐fused pyridiniums. These multicomponent reactions exhibit excellent regioselectivity for 1,3‐diynes, paving a path to the cascade cyclization of 3‐fluoropyridine or N‐methylpyridin‐3‐amine with 1,3‐diynes for the construction of brand‐new tricyclic‐fused pyrano‐ or hydropyridoquinolizinium salts. These ionic fluorophores have been investigated as potential biomarkers.

Cascade One‐Pot Synthesis of Orange‐Red‐Fluorescent Polycyclic Cinnolino[2,3‐f]phenanthridin‐9‐ium Salts by Palladium(II)‐Catalyzed C−H Bond Activation of 2‐Azobiaryl Compounds and Alkenes

“…On the basis of previous TM-catalyzed directing-groupassisted C À Hb ond olefination/annulation reactions, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] we propose the following mechanism for the present reaction (Scheme 4a): First, the catalytic cycle is most likely initiated by coordination of the diazo group to ap alladium species, followed by ortho CÀHa ctivation to form as ix-membered palladacycle D1. [a] Unless otherwise mentioned, reactions were carried out using a2azobiaryl 2 (0.10 mmol), an alkene 3 (0.20 mmol), Pd(OAc) 2 (10 mol %), Cu(OAc) 2 (0.30 mmol), CuCl 2 ·(0.30 mmol), and TFE (2.0 mL) at 110 8 8C for 16 h. Yields are for the isolated product.…”

“…[15a, 16] Later, several research groups also successfully developed aT M-catalyzed synthesis of quaternary ammonium salts. [17] Importantly,t he synthesis of cinnoline and cinnolinium salts by rhodium-catalyzed C À Hactivation with azobenzenes and alkynes or diazo compounds was reported by several groups. [18] Recently,C heng and coworkers reported an efficient and highly regioselective synthesis of isoindolium salts from 2-phenylpyridine and two equivalents of an alkene under rhodium catalysis [Eq.…”

Construction of Cationic Azahelicenes: Regioselective Three‐Component Annulation Using In Situ Activation Strategy

“…To surmount the limitations of the prefunctionalization of pyridines, the in situ activation strategy of pyridines has recently been documented as a facile tool to manipulate the multicomponent cycloaddition reactions [13] . Very recently, our group reported a ring‐fused pyridinium synthesis via a rhodium‐catalyzed three‐component C−H activation/annulation relay of alkyne, simple pyridine and 1,2‐dichloroethane (DCE), in which DCE plays triple roles including solvent, in situ activating agent for pyridine, and vinyl equivalent [14] . Herein we wish to disclose that the cationic azahelicenes can be constructed concisely in one step through a three‐component annulation reaction of isoquinoline with indole in the presence of DCE (Scheme 1 d).…”

Transition Metal‐Catalyzed Intermolecular Cascade C−H Activation/Annulation Processes for the Synthesis of Polycycles

“…In 2018, You's group reported a rhodium(III)‐catalyzed three‐component annulation reaction of simple pyridines, 1,3‐diynes, and 1,2‐dichloroethane (DCE) for the construction of tricyclic pyrano‐ or hydropyridoquinolizinium salts (Scheme 21). [43b] The reaction proceeded in excellent regioselectivity, whereas DCE had to be used as solvent. DCE not only acts as a vinyl equivalent but also as an in situ activating agent for pyridine C−H activation.…”