- Synthesis of multi-substituted 1,2,4-triazoles utilising the ambiphilic reactivity of hydrazones
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The synthesis of N-alkyl-1H-1,2,4-triazoles from N,N-dialkylhydrazones and nitriles via formal [3+2] cycloaddition including the C-chlorination/nucleophilic addition/cyclisation/dealkylation sequence was developed. This sequential reaction utilising the in situ generation of hydrazonoyl chloride based on the ambiphilic reactivity of hydrazones afforded a variety of multi-substituted N-alkyl-triazoles in high yields. The synthetic utility of multi-substituted triazoles was also demonstrated by further transformations.
- Matsuzaki, Haruo,Takeda, Norihiko,Yasui, Motohiro,Okazaki, Mayuko,Suzuki, Seishin,Ueda, Masafumi
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p. 12187 - 12190
(2021/11/30)
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- Aza-enamines, VIII. - Electrophilic Substitution reactions at the Azomethine C-Atom of Aldehyde Dialkylhydrazones: Vilsmeier Formylation and Consecutive Reactions
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The reaction of hydrazones 1 with the Vilsmeier reagent yields 3-phenyl-1,4,5-triaza-1,3-pentadienium salts according to their aza-enamine character.Hydrolysis of 2 gives 1-phenylglyoxal 1-dialkylhydrazones 3, which rearrange in acidic media to 1-phenylglyoxal 2-dialkylhydrazones 4.Compound 3h forms the dihydropyrroloimidazole 5 in boiling ethanol.Pyrrolotriazinium salt 6 is obtained by the reaction of 1b with the isolated Vilsmeier reagent from dimethylformamide/oxalyl chloride.
- Brehme, Rainer
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p. 2039 - 2046
(2007/10/02)
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- Reduction of Nitrosamines with Aqueous Titanium Trichloride: Convenient Preparation of Aliphatic Hydrazines
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The reduction of selected nitrosamines by aqueous TiCl3 has been investigated.In general, aliphatic nitrosamines were converted in good yield to the corresponding hydrazines, with little overreduction to the amines.Reaction proceeded rapidly at room temperature in both alkaline and acidic media.A variety of N,N-dialkylhydrazines have been isolated by using the TiCl3 method, which compares favorably with previously reported procedures for preparatively converting nitrosamines to hydrazines.In the reduction of N-nitroso-N-methylaniline, the proportion of amine in the product increased significantly as the pH of the reaction mixture was lowered, presumably reflecting the known instability of arylalkylnitrosamines in strong acid, coupled with a ready reducibility of the corresponding Fischer-Hepp intermediates; some tendency toward reductive cleavage of the N-aryl-N-alkylhydrazine's N-N-bond was also noted.Reduction of an α-nitrosamino ether gave the monoalkylhydrazine as the major product, while all other reducing agents studied converted this starting material chiefly to a mixture of primary and secondary amines.
- Lunn, George,Sansone, Eric B.,Keefer, Larry K.
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p. 3470 - 3473
(2007/10/02)
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