“…It has been reported that N -acyl-2-hydroxyindoxyls exist in equilibrium with their open-chain tautomers, o -acylaminobenzils, especially in less polar solvents, such as deuteriochloroform. , The presence of the open-chain isomer 2 ‘ (Figure ), at least in deuteriochloroform solution, was in our case easily ruled out by the appearance of signals due to C-2 and C-3 (see above) and the lack of the additional signal due to the keto carbonyl (δ near 200) of 2 ‘ (Figure ).…”
Section: Resultsmentioning
confidence: 47%
“…The fact that 4 was obtained from 1e thus additionally supports the mechanism proposed in Scheme . For the benzoin B it is known to exist in the equilibrium with the dihydrodiol C . − A rapid oxidation of the latter removes it from the equilibrium, giving 2 . Such a facile oxidation of indole-2,3-dihydrodiols has been reported by several authors. ,5a,, 2 …”
Ring contraction of 3-hydroxy-2,4(1H,3H)-quinolinediones (1) in aqueous potassium hydroxide resulted in the formation of 2-hydroxyindoxyls and/or dioxindoles. The choice of N-substituent and the reaction conditions govern the chemoselectivity of the reaction. N-Phenyl-substituted derivatives 1 give 2-hydroxyindoxyls, while N-alkyl- and N-benzyl-substituted derivatives afford the corresponding dioxindols. On the basis of byproduct analysis, as well as independent experiments, the most plausible reaction mechanism is proposed.
“…It has been reported that N -acyl-2-hydroxyindoxyls exist in equilibrium with their open-chain tautomers, o -acylaminobenzils, especially in less polar solvents, such as deuteriochloroform. , The presence of the open-chain isomer 2 ‘ (Figure ), at least in deuteriochloroform solution, was in our case easily ruled out by the appearance of signals due to C-2 and C-3 (see above) and the lack of the additional signal due to the keto carbonyl (δ near 200) of 2 ‘ (Figure ).…”
Section: Resultsmentioning
confidence: 47%
“…The fact that 4 was obtained from 1e thus additionally supports the mechanism proposed in Scheme . For the benzoin B it is known to exist in the equilibrium with the dihydrodiol C . − A rapid oxidation of the latter removes it from the equilibrium, giving 2 . Such a facile oxidation of indole-2,3-dihydrodiols has been reported by several authors. ,5a,, 2 …”
Ring contraction of 3-hydroxy-2,4(1H,3H)-quinolinediones (1) in aqueous potassium hydroxide resulted in the formation of 2-hydroxyindoxyls and/or dioxindoles. The choice of N-substituent and the reaction conditions govern the chemoselectivity of the reaction. N-Phenyl-substituted derivatives 1 give 2-hydroxyindoxyls, while N-alkyl- and N-benzyl-substituted derivatives afford the corresponding dioxindols. On the basis of byproduct analysis, as well as independent experiments, the most plausible reaction mechanism is proposed.
“…: The reaction of (2) with (3a) in boiling benzene afforded the indolone (8) in 78% yield. Therefore, the thermal transformation of (7) to ( 8) was attempted, but, in contrast with (4), no reaction occurred on heating (7) in refluxing benzene. However, by heating (7) in the presence of the ylide (3a) or triethylamine, the transformation smoothly occurred.…”
Section: Resultsmentioning
confidence: 99%
“…A solution of the indolone (2) (0.327 g, 1.7 mmol) and the ylide (3a) (1.63 g, 5.1 mmol) in benzene (5 ml) was heated under reflux for 1 h. After removal of the solvent, the residue was purified by column chromatography on silica gel with methylene chloride-ethyl acetate (6:l) as eluant to give the indolone (8) (0.31 g, 78%), whose IR and 'H NMR spectra were identical with those of the sample obtained in the preceding experiment. (7) to the Indolone (8).+a) Reaction in the presence of the ylide (3a). A solution of the indole (7) (31 mg, 0.13 mmol) and the ylide (3a) (43 mg, 0.13 mmol) in benzene (1.5 ml) was heated under reflux for 1.5 h. The reaction mixture was concentrated under reduced pressure.…”
Section: Reaction Of L-acetyl-2-hydroxyindol-3(2h)-one (2) With the S...mentioning
The Wittig reaction of 1 -acetyl-2-methoxy-(1) and 1 -acetyl-2-hydroxyindol-3(2H)-one (2) with stabilized and semistabilized ylides gave predominantly 3-alkylidenedihydroindoles (4), ( 7 ) , and (1 3) with (2) -stereochemistry. When the Wittig reaction was carried out under more drastic conditions, the Wittig products ( 4) and ( 7) isomerized to afford 3-alkylindoles ( 5) and the indol-2-one (8), respectively. These isomerizations are also described.The Wittig reaction is a powerful method for the stereocontrolled construction of carbon-carbon bonds.' It has recently been reported that a-oxygenated ketones react with stabilized ylides to give predominantly allylic oxygenated (E)alkenes,2 while with nonstabilized ylides mainly (Z)-alkenes are ~b t a i n e d . ~Previously we briefly reported the reaction of stabilized ylides with the 2-methoxyindolone (1) as the aoxygenated ketone which was employed as a key step in a synthesis of the carbazole alkaloid hyella~ole.~ We now report the stereoselective Wittig reaction of the 2-oxygenated indolones (1) and (2) with stabilized and semistabilized ylides to give preferentially (2)-2-oxygenated 3-alkylidenedihydroindoles (4), (7), and (13), and their thermal isomerization to the indoles (5) and the indolone (8).
“…16 However, the isomeric structure (3a') derived from l a ' was easily ruled out by the appearance of the signals due to 3a-C (6 91.1 ppm) and 8a-C (6 113.0) and the lack of the signal due to the koto carbon (6 near 200). '4a~ Thus, when 2-phenylindol-3-one ( l a ) was treated with 2 a in the presence of sodium carbonate at room temperature for 44 h, 3a-hydroxyfwo[2,3-blindole (3a) was obtained in 44% yield.…”
The reaction of 2-hydroxyindol-3-ones (1) with dimethyl acetylenedicarboxylate (2a, DMAD) in the presence of base (triethylamine or sodium carbonate) underwent Michael addition followed by cyclization to produce 3ahydroxyfuro[2,3-hlindoles (3). Compounds possessing furo[2,3-blindole skeleton are of interest in connection with their possible biological activities, represented by the Calabar bean alkaloid physovenine' and the akuammiline alkaloid aspidod a~~c a q i n e .~ A number of approaches to this skeleton are known: electrophilic addition-cyclization of tryptopholes,3 reductive cyclization of oxindole-ethanols and -acetates,4 Baeyer-Villiger oxidation of indol~butanone,~ reaction of indolylmagnesium bromides with ethylene oxide,6 reaction of 2-indolyl sulfoxide with ketene,7 reaction of indoles with dimethyl acetylenedicarboxylate (DMAD),' copper catalyzed reaction of isatin-3-hydrazone with DMAD? Knoevenagel reaction-cyclization of isatin,'' and others."-'3 The reaction of a-hydroxy ketones with acetylene compounds affords furan compounds.'4 In connection with our studies on the chemistry of indol-3-ones,'5 we here report the reactions of 2-hydroxyindol-3-ones (1) with acetylene compounds (2) by means of the addition-cyclization of l a , b with DMAD (2a) giving furo[2,3-blindole derivatives (3). 1 a : R'= AC, R' = ~h 2 a : R = C02Me, R'= Me b : R1= Ac. R 2 = Me b : R = H, R'= Et c : R'= Ac. R2 = H c : R = M e , R ' = E t d : R'= H. R2 = CH2CH=CH2
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