Isatins, rearrangement

Several examples are known of the ring-expansion reactions that transform isatins into quinazolines. iV-Carbamoyl isatins rearrange in the presence of amines into derivatives of 4-carboxy-4-hydroxy-3,4-dihydroquinazolin-2(lH)-ones, and iV-carbamoyl-3-(dicyano)methylene oxindoles provided 4-(dicyano)methylene-3,4-dihydroquinazolin-2(l//)-ones. The two isomeric A-oxides 102 and 103 underwent ring expansion on photolysis and produced the same 1,3-disubstituted quinazoline-2,4-diones (104) among other products, which include isatins. The ratio of products was sensitive... 

Piperidinomethylisatin on lithium aluminum hydride gave the indoline 67 while sodium borohydride reduction of the same isatin derivative gave a reductive dimerization to 68 and a reduction-rearrangement to 69.255... 

Treatment of a number of isatin-3-oximes with sodium methoxide at 140°293 or simply thermally274,294 leads to o-aminobenzonitriles. Thermal treatment of isatin-2-oxime gave isatin and 79.294 Beckman rearrangement of isatin-3-oximes resulted in the formation of o-cyano-phenylisocyanates.26,295 With the Vilsmeier reagent, phosphorus... 

The formation of phosphates 90 can be explained by phosphonate-phosphate rearrangement catalyzed by bases [84], The authors of [82] were able to show that phosphonates 89 react with isatin (in the presence of sodium alkoxide), leading to compounds 90. 

A different pattern is observed in the mass spectra of isatin-3-oximes, where a peak corresponding to the loss of CO is not found this is attributed to a Beckmann rearrangement... 

Indoles and azaindoles undergo smooth oxidation with 2-iodoxybenzoic acid in the presence of indium(lll) chloride (aqueous media, 80 °C) to afford the corresponding isatins in excellent yields <2007S0693>. A peculiar rearrangement to 3//-benzo[< ]indole during the NiS-catalyzed dehydrogenation of 4,5-dihydro-l//-benzo g]indole (350 °C) was reported <2007MC296>. 

Hydroxycinchoninic acid has been prepared by the rearrangement of N-acetylisatin in alkali, -by the treatment of isatin with malonic acid in glacial acetic acid, and by heating cinchoninic acid with concentrated potassium hydroxide. ... 

The gas-phase pyrolysis of benzotriazole leads to a Wolff-type rearrangement to 1-cyanocyclopentadiene in nearly quantitative yield 1% of aniline is formed as a by-product (Eq. 22).76,77 The same products are formed by thermal extrusion of 2 CO from isatin.76 Using methyl-substituted isatins, it was shown that the imidoylcarbene and/or diradical intermediates interconvert to the extent of 10-12% via l//-benzazirine prior to formation of... 

An interesting sequence of reactions used in the preparation of the quinolone derivative (25) has been presented.22 The isatin (26) was treated with base to afford the Pfitzinger rearrangement product (27). Although treatment of (27) with polyphosphoric acid gave the y-lactone (28), reaction in refluxing dimethyl-aniline produced the (5-lactone (29). Successive treatment of the latter with phosphorus oxychloride and potassium hydroxide gave the furoquinoline (25). 

Taylor and Eckroth100 have recently investigated the mechanism of the acid-catalyzed conversion of o-nitrobenzoyldiazomethane (104) to iV-hydroxyisatin (105), discovered by Arndt et al.101 Labeling studies with 14C in the diazo carbon atom gave results which ruled out a Wolff rearrangement, as all the label appeared in the isatin C-2 position. The following mechanistic pathway (104 -> 105) is favored over an alternative one proposed earlier by Moore and Ahlstrom.102... 

Several other reactions of isatin derivatives will now be described. Isatin-2-oxime (93) underwent a Beckmann-like rearrangement to quinazoline-2,4-dione when heated with dilute sodium hydroxide (no yield given).107... 

Some ring-expanding reactions leading to annelated pyrimidines will now be considered. The transformation of isatin-3-oxime (120) to 4-amino-quinazoline was described in Section VI,A,4. Isatin-2-oxime, when heated in dilute sodium hydroxide, rearranged to quinazoline-2,4-dione.383 Isatin-3-imine in alkaline hydrogen peroxide was converted to the same substance in excellent yield.384... 

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