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A convenient one-step synthesis of symmetrical 1,1¢-dialkyl derivatives of isoindigo is described.In recent years, isoindigo (3,3¢-biindolinylidene-2,2¢-dione) and especially its N-and N,N¢-derivatives have attracted great attention not only as dyes, but also as substances that possess specific biological activity (antileukemia, antiproliferative, anti-inflammatory, etc.). [1][2][3][4] Thus, 1-(b-D-glucopyranosyl)isoindigo was found to be an antileukemia drug. 2-4 It has to be noted that the synthesis of 1-substituted isoindigos is often a multistep procedure. The best approach to the synthesis of isoindigo derivatives seems to be the dimerization of ketocarbenes generated from isatin derivatives. It has been assumed 5,6 that a mixture of 3-(triphenylphosphoranylidene)-1,3-dihydro-2H-indol-2-one and isoindigo is formed with moderate yield by the reaction of triphenylphosphine with isatin and 1-methylisatin through intermediate carbene formation. However, generation of carbenes from heterocyclic a-diketones under the action of trivalent phosphorus derivatives has been insufficiently studied. 7,8 Recently for the examples of acenaphthenequinone 9 and 1-acetylisatin, 10 we have shown that tris(diethylamino)phosphine is a more convenient reagent for a-ketocarbene generation. We have succeded 11 in trapping acenaphthenone carbene by fullerene C 60 . Herein we report the synthesis of some new isoindigo derivatives. The treatment of isatin derivatives 1 with tris(diethylamino)phosphine in dichloromethane at -60 °C for 10 minutes furnished tris(diethylamino)phosphine oxide (d P = 24.3) and the corresponding 1,1¢-disubstituted 3,3¢-biindolinylidene-2,2¢-diones (1,1¢-dialkylisoindigos) 2 in 60-91% yield (Scheme 1). The regiochemistry of deoxygenation at C3 in all cases was unequivocally established using 13 C NMR spectra data. The 13 C NMR spectrum of compound 2e displayed a signal at d = 167.8 as a triplet with spin-spin coupling constant 3 J HCNC = 3.5 Hz due to the two methylene protons, indicating the presence of one carbonyl group. The signal of C3 appeared at d = 133.5 as a doublet with 3 J HCCC = 2.6 Hz due to the proton at C4. Other spectral data also confirm the assigned structure of compounds 2a-e.A plausible mechanism of the reaction is shown in Scheme 2. It is reasonable to assume that the first stage of the reaction includes a one-electron transfer from phosphorus to the heterocyclic system to form ion radical pair 3. The next stage is likely to include the formation of the phosphonium salt 4 having a P-O-C fragment. Then this intermediate eliminates tris(diethylamino)phosphine oxide to give carbene 5, which under the reaction conditions undergoes dimerization to form the final products 2.In conclusion, a facile and convenient synthesis of isoindigo derivatives was achieved through a deoxygenation reaction of various 1-alkylisatins with tris(diethylamino)phosphine. The key step for the formation of a variety of isoindigos is a mild carbene generation followed by carbene dimerization. This methodology has sever...

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A simple and easy condensation reaction of aryl‐ or N‐substituted isatins with Girard's reagents P and T was found to be useful in obtaining of water‐soluble isatin‐based quaternary ammonium compounds (QACs) bearing pyridinium or trimethylammonium moiety with high yields. Their antimicrobial activity was evaluated. Selective activity against Gram‐positive bacteria (S. aureus 209p and B. cereus 8035) and yeast‐like fungus Candida albicans 855–653 was shown. The influence of the substituent's nature as in the aromatic fragment as at position 1 on the activity was established. The most active are the pyridinium salts containing sterically hindered phenolic fragment at the position 1 of the heterocycle. The structures of all novel compounds were fully characterized using IR and NMR spectroscopies as well as XRD analysis.