From arylhydrazones

The 1,3-dipolar cycloaddition of diarylnitrile imines 98, generated in situ from arylhydrazones with chloramine T or from a-chlorobenzylidenephenylhydrazine with triethylamine, to some 5-substituted 2-methylpyridazin-3(2//)-ones 88, 99-101 has been shown to afford l,3-diaryl-l,5-dihydro-4//-pyrazolo[3,4- ]pyridazin-4-ones 102 regioselectively (Scheme 21) <2000JMT(528)13>. 

Processes include the Fischer indole synthesis from arylhydrazones and related sigmatropic syntheses, reductive evclizations of nitni compounds, the Madelung synthesis from anilides and related base-cululyxed condensations. and transition-metal catalyzed cyclizations,... 

Fischer indole synthesis Preparation of indoles from arylhydrazones of ketones and aldehydes in the presence of protic or Lewis acid catalyst. 172... 

Ginnolines from arylhydrazones via N-alkylideneamino-N-aryloxamyl chlorides and 1-alkylideneaminoisatins Stolle-Becker rearrangement... 

The issue of regioselectivity arises with arylhydrazones of unsymmetrical ketones which can form two different enehydrazine intermediates. Under the conditions used most commonly for Fischer cyclizations, e g. ethanolic HCI, the major product is usually the one arising from the more highly substituted enehydrazine. Thus methyl ketones usually give 2-methy indoles and cycliz-ation occurs in a branched chain in preference to a straight chain. This regioselectivity is attributed to the greater stability of the more substituted enhydrazine and its dominance of the reaction path. 

Another issue of regioselectivity arises with meta-substituted arylhydrazones from which either 4- or 6-substitutcd indoles can be formed. Robinson has tabulated extensive data on this point[9]. A study comparing regioselectivity of cyclization as catalysed by HCl/EtOH and ZnClj was carried out for several m-substituted arylhydrazones of diethyl ketone[10]. The results given in Table 7.1 show some dependence on catalyst but mixtures are obtained under all conditions studied. 

Jacobson-Hugershofi synthesis benzothiazoles, 5, 135 Japp-KJingemann reaction JV-arylhydrazones from, 4, 337 1,2,4-triazole synthesis by, 5, 768 Jasmine lactone synthesis, 3, 847 Jasminine occurrence, 2, 626 y-Jasmolactone synthesis, 4, 674 cis-Jasmone synthesis, 1, 422, 427 Jatropham synthesis, 1, 426 Josephson junctions, 1, 359 Juliprospine... 

The first indolization of an arylhydrazone was reported in 1983 by Fischer and Jourdan" by treatment of pyruvic acid 1-methylphenylhydrazone 3 with alcoholic hydrogen chloride. However, it was not until the following year that Fischer and Hess identified the product from this reaction as 1-methyl indole-2-carboxylic acid 4. 

Surprisingly, arylhydrazones 88a-d, upon treatment with 1-benzenesulfonyl-hydrazide 89 in refluxing ethanol, afforded very good yields of pyrazol-3-ones 90a-d (85JIC54) (Scheme 25). 5-Aminopyrazol-3-(Mies have also been synthesized from /3-cyanoesters (Section II,A,2) and from /3-iminoesters (Section II,A,3). 

Arylhydrazones from reaction of /3-dicarbonyl compounds with arenediazonium salts... 

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-... 

In the presence of sodium acetate in acetic acid, the arylhydrazones 54 (available from the reaction of tu-halogen-tu-(arylhydrazono)acetophenones with 3-amino[l,2,4]triazole) undergo cyclization to yield 3-aroyl-l-aryl-l//-[l,2,4]-tria-zolo[3,4-c][l,2,4]triazoles 55 (Equation 7) <1987CB965>. 

The issue of stereoselectivity of the vinyllithium formed from acyclic arylhydrazones has also been addressed. For symmetrical linear-chain ketone derivatives such as 105, the -vinyllithium 106 is the exclusive product (equation 36)362,367-372... 

Construction of the indole ring via Fischer synthesis. Starting from a variety of 3,4-dihydro-lH-benzo[l ]azepine-2,5-diones 40 and arylhydrazines Fischer syntheses of indolo benzazepinones 41 have been reported (Scheme 8 (1999JMC2909)). Usually, the reaction comprises a two-step one-pot procedure with the formation of intermediate arylhydrazones in warm acetic acid followed... 

The synthesis of cyclic ethers 137 was achieved by a Fischer indole synthesis starting from cyclic keto arylhydrazones generated in situ from 4-(hydroxy-methylene)-3,4-dihydrobenzo[ 7]oxepin-5(2H)-one 136 and the corresponding diazonium salt (Equation (20), 1993JHC1481). 

Mild oxidation of o-nitrobenzaldehyde arylhydrazones with either bromine and sodium acetate or lead tetraacetate results in the overall loss of two hydrogen atoms and production of a class of iV-aryl heterocycles, tiie structure of which was the subject of uncertainty and some controversy for more than fifty years. These oxidation products were first prepared and investigated by Chattawayj " who described them as isodiazomethanes and formulated them as the triaziridine derivates 72. Structural assignment was based entirely on evidence from degradation studies in particular, Chattaway showed that reduction of... 

Alkyl-3-formylcarbazoles form-arylhydrazones " and azines or hydrazones with hydrazine. 9-Ethyl-3-formylcarbazole gives Schiflf bases with arylamines. Variously substituted 3-formylcarbazoles condense with aminoacetal, " and the resulting imines are easily reduced catalytically or with sodium borohydride. Anils from... 

Several examples of the mesoionic 3-aryl-l,2,3,4-oxatriazole-5-oxide ring system 123 have been prepared by cyclisation of the arylhydrazones 122 these in turn are prepared from aryldiazonium salts and bromonitromethane <99KGS413>. 

The tricyanovinylpyrazoles 67, isolated from reaction of tetracyanoeth-ylene (TCNE) with 51 (R1 = H,Ph R2 = H, Me), cyclized in refluxing acetic anhydride to 68.76 Analogous products (68 R1 = Ar,R2 = Me) were obtained from thermolysis or photolysis of the charge-transfer complex 69 formed between TCNE and arylhydrazones.77... 

Ilac Fischer indole synthesis from /V-arylhydrazones 3.06.3.4.2... 

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