Hydrazones from active methylene compounds

From activated methylene compounds and 1,2-diaza-l,3-butadienes. The activated methylene group of pyrroles 189a,b,d, under basic conditions in tetrahydrofuran, attacked C-4 of 1,2-diaza-l, 3-butadienes 190a-d to give the hydrazones 191a-e as diastereomeric mixtures (02S1546) (Scheme 43). Cyclization of these derivatives in the presence... 

Several 3-(2H)pyridazinones have been prepared from monophenyl hydrazones of 1,2-dicarbonyl compounds and a variety of active methylene compounds within 1-20 min without solvent under focused irradiation in the presence of carefully adjusted amounts of piperidine or solid potassium tert-butoxide (isolated yields 50-89%), in accordance with Scheme 8.49 [72, 73]. 

Numerous methods to prepare individual classes of aliphatic diazo compounds have been extensively developed. The major strategies for their synthesis involve the alkaline cleavage of N-alkyl-N-nitroso-ureas, -carboxamides and -sulfonamides, dehydrogenation of hydrazones, as well as diazo group transfer from sulfonyl and related azides to active methylene compounds, and electrophilic diazoalkane substitution reactions. These synthetic methods have been comprehensively reviewed (15,16). Useful information on the preparation of selected diazo compounds can be found elsewhere (6,17). 

Dimethylaminonitroethylene is prepared from the anion of nitromethane and the salt prepaffed from dimethylformamide and dimethyl sulfate. The condensation step is general for other types of active methylene compounds, indicating further potential for pyrrole synthesis. A related process involves the condensation of ketones with the moao-N,N-dimethylhydrazone of glyoxal base-catalyzed condensation affords the hydrazones of a conjugated 1,4-dicarbonyl system, and sodium thiosulfate reduction then affords 2,3-disubstituted pyrroles (equation 85) (77CB491). 

Regitz diazo transfer reactions have been reviewed previously.1-3 The following two main routes have been known for the synthesis of diazo compounds (1) diazotization of amines, oximes, nitrosoamines, and hydrazones (2) transfer of the diazo function from tosyl or mesyl azides to active methylene compounds. 

Several 3-(2H)-pyridazinones have been prepared from monophenyl hydrazones of 1,2-dicarbonyl compounds and a variety of active methylene compounds within 1-20 min without solvent under focused irradiation conditions in the presence of carefully adjusted amounts of piperidine or solid potassium tert-butoxide (isolated yields 50-89%), in accordance with Scheme 10.109 [216]. In the synthesis of the pyridazinone 44, microwave irradiation has no specific effect, because the result (72%) was identical with that obtained by use of classical heating under the same conditions. With the dry media procedure it was possible to isolate the intermediate alkene, which was not obtained in the previously reported procedure. When the active methylene compound is a keto ester, the reaction follows a different pathway [216b]. 

The synthetic utility of this base (1) was demonstrated in the preparation of vinyl iodides in high yields from simple ketohydrazones and iodine (Table), a process that normally gives mixtures of vinyl iodides and geminal diiodides if less hindered bases are employed.6 This base has also been used in the elimination of sulfonic acids from the corresponding sulfonates, the alkylation of compounds containing active methylene groups, the conversion of hydrazones to vinyl selenides, and the preparation of esters from sterically hindered acids.4 5... 

In analogous fashion, the basicity of the azole ring affects the ring closure to azolo-triazines 182 of the hydrazones 181 obtained from the coupling reaction of diazoazoles and methylene active compounds (76JMC517). 

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