Arylhydrazines, rearrangement

Other non-traditional preparations of 1,2,3-triazoles have been reported. The rearrangement in dioxane/water of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole into (2-aryl-5-phenyl-27/-l,2,3-triazol-4-yl)ureas was investigated mechanistically in terms of substituents on different pathways <06JOC5616>. A general and efficient method for the preparation of 2,4-diary 1-1,2,3-triazoles 140 from a-hydroxyacetophenones 139 and arylhydrazines is reported <06SC2461>. 5-Alkylamino-] //-], 2,3-triazoles were obtained by base-mediated cleavage of cycloadducts of azides to cyclic ketene acetals <06S1943>. Oxidation of N-... 

JOC8210>. Condensation of succinaldehyde with arylhydrazines and benzotriazole gives 1-aminopyrrolidines 646 that upon treatment with organomagnesium reagents rearrange to 1,4,5,6-tetrahydropyridazines 647 <1998S1627>. 

The reaction of 2-substituted-5-aroyl-isothiazol-3-ones (214) with hy-droxylamine or arylhydrazines gives the 1,2,5-oxathiazoles 216 (Z = O) or 1,2,3-thiadiazoles 216 (Z = NAr ), as a result of a spontaneous rearrangement of unisolated oximes 215 (Z = O) or arylhydrazones 215... 

Acyl substituents at the 3- and/or 4-positions result in decreased hydrolytic stability compared with the alkyl and aryl derivatives described above. Despite this constraint most of the usual reactions of the carbonyl group are possible. Aldehydes <9ILA1211> and ketones are oxidized to the carboxylic acid, borohydride reduction affords the expected alcohols, and epoxides are formed on reaction with diazomethane. Oximes and arylhydrazones are formed with hydroxylamine and arylhydrazines, and the products may subsequently undergo monocyclic rearrangement involving the oxadiazole to give the corresponding isomeric furazans and 1,2,3-triazoles (Section 4.05.5.1.4). 

Rousselle, D., Musick, C., Viehe, H. G., Tinant, B., Declercq, J. P. Tris-aza-Cope rearrangement of bicyclic N-cyano-N -vinyl or N -arylhydrazines to imidazolodiazepine derivatives. Tetrahedron Lett. 1991, 32, 907-910. 

The arylhydrazine derivatives can also participate in other than benzidine isomeriza-tions. Thus, a novel rearrangement of fused /V-arylamino-substituted 1,4-dihydropyridines 137 resulted in the formation of quinindoline derivatives 1392 30,231 (equation 53). A proposed mechanism of this reaction assumes a [3,3]-sigmatropic shift like a Cope rearrangement through unstable intermediate 138. 

The reaction of triethyl l,3,5-triazine-2,4,6-tricarboxylate (16) with arylhydrazines proceeds with rearrangement and leads to imidazol-4-ones 18 in yields of 53 to 94%.22,23 These conversions are conducted in refluxing ethanol for 2 hours. 

Aromatic-aliphatic azo compounds can without exception be prepared by oxidation of the corresponding JV-alkyl-A -arylhydrazines. The oxidant must be one that reacts in neutral or alkaline conditions since the azo product rearranges to arylhydrazone in an acid medium. Mercury(n) oxide, introduced by Emil Fischer341 as oxidant, is almost always used for this reaction. 30% Hydrogen peroxide in hydrogen carbonate solution has been applied to dehydrogenation of A-aryl-A -(triphenylmethyl)hydrazines with good results.342... 

Hydroxycoumarin is converted in high yield by aryl-iodonium acetates [e.g., PhI(OAc)2] into the betaines (158) which rearrange in hot acetic acid to the 3-iodocoumarin (159) and are converted by hydrochloric or hydrobromic acid into 3-chloro- or 3-bromo-4-hydroxycoumarin.171 On reaction with arylhydrazines, 3-acetyl-4-hydroxycoumarin is converted into pyrazoles (160) which are cyclized to the benzopyrano[2,3-c]pyrazol-4-ones (161).172... 

An important type of aromatic Claisen rearrangement occurs in the Fischer indole synthesis. " The Fischer indole synthesis involves the condensation of an arylhydrazine with an aldehyde or ketone to give an arylhydrazone, which, in the presence of a catalyst undergoes rearrangement and elimination of ammonia to give the indole ring. One of many different protic or Lewis acid catalysts can be used. For example, Woodward s synthesis of strychnine commenced with the condensation of the ketone 303 and phenylhydrazine in the presence of polyphosphoric acid to give the indole 304 (3.194). 

An extraordinarily simple approach to a Fischer indoli-zation is that of Taylor and Donald [120] involving the transformation of epoxides to indoles via aldehydes or ketones (the Meinwald rearrangement) in the presence of arylhydrazines, and thence to indoles, obviating the need for isolating the carbonyl compound. Selected examples of this simple chemistry are shown in Scheme 18 (equations 1, 2). Of the Lewis acids screened, scandium(III) triflate proved to be superior. Greaney and colleagnes... 

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