Aromatic hydrazones

If the hydroformylation of olefins is conducted in the presence of aromatic hydrazines and Bronsted or Lewis acids indoles can be obtained directly in one pot [91-93,95]. Hydroformylation of the olefin gives an intermediate aldehyde, which is trapped immediately by the present aromatic hydrazine as an aromatic hydrazones similar to the formation of imines under hydroformylation conditions. Under acid mediation these aromatic hydrazones undergo a Fischer indolization, consisting of a [3,3]-sigmatropic rearrangement followed by a cyclization and elimination of ammonia (Scheme 38). 

Scheme 6.97 Typical products obtained from the 91-catalyzed asymmetric allylation of N-benzoyl-protected aromatic hydrazones. The product configurations were not determined.

Variations to the radical acceptor component were also examined with a series of aldehyde hydrazones (Table 3, entries 7-15) [48]. Branching at a saturated a-carbon diminished the yields (entries 7-10), but the aromatic hydrazone 7 allowed successful radical addition (entries 11-14). The reactions were generally quite clean with the exception of 8a, which decomposed under these conditions (entry 15). It should be noted that low yields were accompanied by unreacted hydrazones 80-90% mass balance was generally observed. 

Very dilute fluorine was reacted with aromatic hydrazones to produce a benzylic CF2 moiety (equation 174)294. Aromatic fluorination with elemental fluorine had also been attempted. Purrington and Woodard found that ortho fluorination usually took place with systems carrying either electron-donating or electron-withdrawing substituent, although neither the yields nor the conversions were very high. They studied the influence of strong... 

The nitro-substituted seleninic acid 103a was also found [531 to be an effective catalyst for the hydrogen peroxide mediated oxidative conversion of aromatic hydrazones 107 into nitriles 108 (Eq. 21). However, oxidation of hexanal dimethylhydrazone with this system gave only the parent aldehyde. 

Aromatic hydrazones 390 are converted into the corresponding tosylates 391 in high yield upon reaction with [methoxy(tosyloxy)iodo]benzene (MTIB) in dichloromethane (Scheme 3.156) [482]. 

This reaction was first reported by Fischer and Jourdan in 1883. It is a synthesis of indole derivatives by the treatment of aryl hydrazones coupled from aromatic hydrazines and ketones or aldehydes with either a mineral or Lewis acid. Therefore, it is generally known as the Fischer indole synthesis. In addition, it is also referred to as Fischer cyclization, Fischer indole cyclization, Fischer indole reaction, Fischer indolization, Fischer reaction, and Fischer indole annulation. Although the mechanism has been extensively studied, the one formulated by Robinson and Robinson is now generally accepted. It involves the following steps (a) initial acid-catalyzed tautomerization of an aromatic hydrazone to an ene-hydrazine, b) a [3,3]-sigmatropic rearrangement of ene-hydrazine to a M-imine intermediate, (c) re-aromatization to aniline, d) intramolecular nucleophilic attack to form aminal, and (e) extrusion of an ammonia to afford the indole. 

In addition to the classes of compounds considered, epoxy compounds [58] azomethyne derivatives of o- and p-aminophenols [59], aromatic hydrazones [60], organic zinc compounds [61], tin dibulyl mer-captide, salts of metals of groups II and IV of the Periodic System and organic acids containing from 8 to 24 carbon atoms in the molecule [62], alkaline salts of mercaptans, in particular, mercaptobenzimidazole [28], and a number of others have been recommended and tested as stabilizers of polymers. Most of these recommendations were taken from data on the stabilization of other classes of polymers and are not specific for polyolefins. 

Fischer-Hepp rearrangement org chem The rearrangement of a nitroso derivative of a secondary aromatic amine to a p-nitrosoarylamine the reaction is brought about by an alcoholic solution of hydrogen chloride. fish ar hep re a rani mant) Fischer indole synthesis orgchem A reaction to form indole derivatives by means of a ring closure of aromatic hydrazones.. fish ar in.dol. sin tha sas )... 

Meanwhile, the photoreactions of some ahcycHc and aromatic hydrazones and their acetyl derivatives were investigated by Suginome and Uchida, disclosing photochemical reactions other than the E,Z-isomerization. " ... 

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