Arylhydrazones, review

Octanal 2,4-dinitrophenylhydrazone refluxed 1.5 hrs. in ethylene glycol-water containing KHCOg under an oil trap octanal. Y 63°. - Similarly Citronellal. Y 60%. F. e., also ketones, s. G. W. O Donnell, Australian J. Chem. 21, 271 (1968) arylhydrazones, review s. J. Buckingham, Quart. Reviews 23, 37 (1969). 

The cyclization of the phosphorylated arylhydrazones, leading to compounds 168, presumably takes place through the initial formation of 3-phosphorylated indoles 69, which isomerize to compounds 168 in the course of the reaction. Such 3—>2 rearrangements are well-known [30, 180-182, 231]. The transposition of the phosphorus-containing substituent in indoles was first observed in [178, 179]. In the review [8] the data on the formation of 2-phosphorylindoles from the arylhydrazones of phosphorylpropionic aldehyde were considered proved, but the results on the cyclization of hydrazones of phosphorylacetaldehyde to the 2-isomers were placed under some doubt. 

A study of the Tables at the end of this review will reveal that a wide range of amines has been used to prepare compounds of the type under discussion. They include ammonia, and primary and secondary aliphatic, alicylic, and aromatic amines, as well as many heterocyclic amines. The methods used for preparing arylhydrazones of sugars (and the properties of these compounds) have many similarities with those for glycosylamines. These hydrazones have been surveyed by Percival. ... 

The best known and most significant Fischer indolization variation is that of Japp and Klingemann, described in 1887 [138] and 1888 [139] and reviewed by Phillips in 1959 [140] and Li in 2007 [141], This reaction involves the union of an aryldiazonium salt with a 1,3-dicarbonyl compound to give the requisite arylhydrazone following loss of one of the carbonyl fragments (Scheme 25). Examples of the Japp-Klingemann reaction are combined with the normal Fischer indolization in the AppUcations section. 

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