Reaction of a brominated benzolactone/lactam with 4-methoxythiobenzamide and thiourea: an Eschenmoser coupling reaction, ring transformation, or dimerization?

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

“…The preliminary experiments involving the reaction of 1a with N , N -dimethylthiobenzamide ( 4a ) in DMF have shown that the reaction is much slower (>24 h) and also gives relatively high amounts of the undesirable isoindigo 9a [ 32 ] (route c). In order to accelerate the Eschenmoser coupling reaction and to enhance the reaction yield (route b) an addition of a suitable thiophile assisting the sulfur extrusion should be beneficial [ 36 ].…”

“…The usual method used for the configuration assignment of 3-amino(aryl)methylidene derivatives involves a simple 1 H NMR experiment showing either an upfield (δ ≈ 5.7–6.4 ppm for ( Z )-configuration [ 5 , 12 , 32 – 33 ]) or a downfield shift (δ ≈ 7.7–7.9 ppm for ( E )-configuration [ 27 ]) of the proton in position 4 of the oxindole moiety. In our previous paper [ 32 ] such an assignment was also confirmed in the solid state by X-ray diffraction.…”

“…The usual method used for the configuration assignment of 3-amino(aryl)methylidene derivatives involves a simple 1 H NMR experiment showing either an upfield (δ ≈ 5.7–6.4 ppm for ( Z )-configuration [ 5 , 12 , 32 – 33 ]) or a downfield shift (δ ≈ 7.7–7.9 ppm for ( E )-configuration [ 27 ]) of the proton in position 4 of the oxindole moiety. In our previous paper [ 32 ] such an assignment was also confirmed in the solid state by X-ray diffraction. The important role of the intramolecular hydrogen bond fixing the ( Z )-configuration has also been observed in the crystal structures of other 3-aminomethylidene derivatives containing a primary or secondary nitrogen [ 14 , 49 – 52 ].…”

“…In our group we recently discovered [ 32 – 33 ] a new synthetic pathway involving a rearrangement of 2-aryl-5-(2-aminophenyl)-4-hydroxy-1,3-thiazoles (e.g., 8aa–ad in Scheme 2 ) leading to the 3-[amino(aryl)methylidene]-1,3-dihydro-2 H -indol-2-ones containing an unsubstituted amino group and the oxindole nucleus. In the present paper, we want to describe an optimized procedure avoiding the intermediary thiazoles and to demonstrate the usefulness and wide group tolerability of our new synthetic approach for the preparation of a library of substituted phenyl and amino derivatives ( Table 1 ).…”

Eschenmoser Coupling Reaction and Reactivity of Hydrazinecarbo­thioamides in the Synthesis of Benzindazole and Naphthothiazole Derivatives

“…Recently, Kammel et al reported that the reaction of 3bromooxindole with substituted (hetero)aromatic-thioamides at room temperature gave thiazole derivatives, whereas at elevated temperatures the products of the Eschenmoser coupling reaction, (arylmethylidene)indolones, were formed. 23,24 Based on the above results, we decided to investigate the behavior of other hydrazinecarbothioamides, namely Nsubstituted 2-tosylhydrazinecarbothioamides 1f,g toward 2,3-dichloro-1,4-naphthoquinone (2). Treatment of 1.1 mmol of 1f,g with 1.1 mmol of 2 applying Eschenmoser coupling reaction conditions gave Table 2).…”