Rh(III)-Catalyzed (4 + 1) Annulation of Pyrazol-3-ones with Alkynoates via Ortho-Alkenylation/Cyclization Cascade: Synthesis of Indazole-Fused Pyrazoles

Abstract

A facile synthesis of novel indazole-fused pyrazoles from pyrazol-3-ones and alkynoate esters/amides via Rh­(III)-catalyzed sequential C–H activation/ortho-alkenylation/intramolecular cyclization cascade is reported. The important characteristic of this method is that the resulting scaffold bearing quaternary carbon has been obtained through unusual [4 + 1] rather than expected [4 + 2] addition where alkynoate acts as a one-carbon unit.

Rh(III)‐Catalyzed C−H Annulation and Spirolactonization of 2‐Aryl‐1H‐benzo[d]imidazoles with 4‐Hydroxy‐2‐alkynoates via C−H bond activation

“…The isolate yield of the minor product 4 was summarized in Table 3. In the above reaction conditions, the corresponding spiro compounds (3 a, 3 b, 3 c, 3 d, 3 e, 3 f) were isolated in 55, 48, 43, 50, 38, 35 % respectively. Based on previous reports, [16,17] a plausible reaction mechanism is proposed in Scheme 3. Initially, a monomeric cationic rhodium complex [Cp*RhCl 2 ] is formed in situ from the dimeric Rh(III) complex and NaOAc, which is highly reactive to activate the ortho-CÀ H bond of arene by coordinating with a nitrogen atom to form a five-membered metallocycle A, Subsequent π- In order to realise the raection pathway, we performed the deuterium exchange experiment, competitive reaction and kinetic isotopic effect in the formation of product 3 a and the results are presented in Scheme 4.…”

“…Based on previous reports, [16,17] a plausible reaction mechanism is proposed in Scheme 3. Initially, a monomeric cationic rhodium complex [Cp*RhCl 2 ] is formed in situ from the dimeric Rh(III) complex and NaOAc, which is highly reactive to activate the ortho ‐C−H bond of arene by coordinating with a nitrogen atom to form a five‐membered metallocycle A , Subsequent π‐complexation of 4‐hydroxy‐2‐alkynoates with metallocycle A generates the ternary complex B .…”

A Novel Method for the Pre-Column Derivatization of Saccharides from Polygonatum cyrtonema Hua. by Integrating Lambert–Beer Law and Response Surface Methodology

“…4-(5-hydroxy-3-methyl-1H-pyrazole-1-yl) benzonitrile 3e was synthesized according to a reported procedure [32][33][34]. In brief, ethyl acetoacetate (2 mmol, 252 µL), glacial acetic acid (0.6 mL), and ethanol (2 mL) were added to commercially available 4-cyanophenylhydrazine hydrochloride (2 mmol, 306.28 mg), and the mixture was reacted at 100 • C for 6 h. A lightyellow solid powder was obtained by silica gel column chromatography, with a yield of 10%.…”

“…PMP derivatives with different substituents (such as 4-H, 4-Br, 4-CH 3 , 4-Cl, 4-OCH 3 , 4-F, 3-F, and 2-F) were synthesized according to the method described above. These compounds were known [32][33][34].…”

DFT Study on Mechanism of Ni–Al Bimetallic-Catalyzed C–H Cyclization to Construct Tricyclic Imidazoles: Roles of NHC Ligand and AlMe3

“…However, over the past few decades, transition metal-catalyzed C–H cyclization − for medium-ring synthesis has been a challenging goal. Early efforts focused on the cyclization of C–H bonds via iridium − and rhodium − catalysts. Until recent years, C–H bond activation using nickel catalysis , to form 7-membered rings has been developed.…”