Hydrazines, addition reactions rearrangement

In addition it may be noted that amides of a, 3-unsaturated adds and of a-hydroxyacids yield aldehydes when allowed to undergo this rearrangement. Aryl-substituted semicarbazides yield azides, and aryl--substituted ureas yield aryl-substituted hydrazines. These reactions are discussed more fully in a subsequent section of this chapter (p. 273). 

In addition to the Dimroth rearrangement of [l,2,4]triazolo[3,4-c][l,2,4]triazines discussed in the last section, derivatives of (42) would probably be accessible by the general application of a special case which involved the reaction of l-acetonyl-5-chloro-l,2,4-triazole (356) with hydrazine to produce the dihydro compound (357). Lead tetraacetate oxidation of (357) formed (358) (77JOC1018). 

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. 

Based on their successes in developing catalytic asymmetric Fischer indole synthesis, List and co-workers further carried out [3,3]-rearrangement reactions of At,At -binaphthyl hydrazines to deliver BINAM products. In this case, (i )-35 was also proved to be the best catalyst. The addition of weakly acidic CG-50 resin as an additive could allow the reaction to be performed at a relatively low catalyst loading (5 mol%). A number of Af,Ar-binaphthyl hydrazine substrates with electronically diverse substituents could be converted to their corresponding products in good yields and enantioselectivity. 

Anthoni and his co-workers, in a comprehensive paper, have described the syntheses of several dithiocarbazic acids by the reaction of differently substituted hydrazines with carbon disulphide. The reaction of 2-amino-ethylhydrazine with carbon disulphide has been reported to give the inner salt (315), which, however, easily rearranges to (316). In addition, the reactions of carbon disulphide with isothioureas, which probably involve... 

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