Formation of 3-[amino(aryl)-methylidene]-1,3-dihydro-2 H -indol-2-ones involving ring transformation of 2-aryl-5-(2-aminophenyl)-4-hydroxy-1,3-thiazoles

Autocatalysis in Eschenmoser Coupling Reactions

The Eschenmoser coupling reaction (ECR) of thioamides with electrophiles is believed to proceed via thiirane intermediates. However, little is known about converting the intermediates into ECR products. Previous mechanistic studies involved external thiophiles to remove the sulfur atom from the intermediates. In this work, an ECR proceeding without any thiophilic agent or base is studied by electrospray ionization-mass spectrometry. ESI-MS enables the detection of the so-far elusive polysulfide species Sn , with n ranging from 2 to 16 sulfur atoms, proposed to be the key species leading to product formation. Integrating observations from ion mobility spectrometry, ion spectroscopy, and reaction monitoring via flow chemistry coupled with mass spectrometry provides a comprehensive understanding of the reaction mechanism and uncovers the autocatalytic nature of the ECR reaction.

Eschenmoser coupling reactions starting from primary thioamides. When do they work and when not?

Reactions of thiobenzamide or thioacetamide with 4-bromo-1,1-dimethyl-1,4-dihydroisoquinoline-3(2H)-one, 4-bromoisoquinoline-1,3(2H,4H)-dione and two α-bromo(phenyl)acetamides were examined under various conditions (base, solvent, thiophile, temperature) and structure/medium features that influence product distribution (Eschenmoser coupling reaction, Hantzsch thiazole synthesis and elimination to nitriles) were identified. The key factor that enables the successful Eschenmoser coupling reaction involves the optimum balance in acidity of nitrogen and carbon atoms of the intermediary α-thioiminium salts.

Synthesis of the Kinase Inhibitors Nintedanib, Hesperadin, and Their Analogues Using the Eschenmoser Coupling Reaction

A novel synthetic approach involving an Eschenmoser coupling reaction of substituted 3-bromooxindoles (H, 6-Cl, 6-COOMe, 5-NO₂) with two substituted thiobenzanilides in dimethylformamide or acetonitrile was used for the synthesis of eight kinase inhibitors including Nintedanib and Hesperadin in yields exceeding 76%. Starting compounds for the synthesis are also easily available in good yields. 3-Bromooxindoles were prepared either from corresponding isatins using a three-step synthesis in an average overall yield of 65% or by direct bromination of oxindoles (yield of 65-86%). Starting N-(4-piperidin-1-ylmethyl-phenyl)-thiobenzamide was prepared by thionation of the corresponding benzanilide in an 86% yield and N-methyl-N-(4-thiobenzoylaminophenyl)-2-(4-methylpiperazin-1-yl)acetamide was prepared by thioacylation of the corresponding aniline with methyl dithiobenzoate in an 86% yield.

Synthesis of (Z)-3-[amino(phenyl)methylidene]-1,3-dihydro-2H-indol-2-ones using an Eschenmoser coupling reaction

A highly modular method for the synthesis of (Z)-3-[amino(phenyl/methyl)methylidene]-1,3-dihydro-2H-indol-2-ones starting from easily available 3-bromooxindoles or (2-oxoindolin-3-yl)triflate and thioacetamides or thiobenzamides is described. A series of 49 compounds, several of which have previously been shown to possess significant tyrosin kinase inhibiting activity, was prepared in yields varying mostly from 70 to 97% and always surpassing those obtained by other published methods. The method includes an Eschenmoser coupling reaction, which is very feasible (even without using a thiophile except tertiary amides) and scalable. The (Z)-configuration of all products was confirmed by NMR techniques.

Transition-Metal-Free Addition Reaction for the Synthesis of 3-(Aminobenzylidene/aminoalkylidene)indolin-2-ones and Its Synthetic Applications

A novel and efficient transition-metal-free approach for the exclusive synthesis of Z-3-(aminobenzylidene/aminoalkylidene)indolin-2-ones in high yield from 2-oxindole and aryl/alkyl nitrile in the presence of LiOtBu and 2,2'-bipyridine system is described. In addition, we disclosed a new approach towards the metal-free fluorination using selectfluor and the C═C bond cleavage using CuI and environmentally benign O₂.