Pyridazin-3-ones, reduction

Few reactions of this type are recorded. The azidopyridazinone ester (349) on reduction with triethyl phosphite, hydrazine or borohydride furnished the pyrido[2,3-c]pyridazin-7-one (350) (79JHC1559), whilst an A-aminopyrido[2,3-c]pyridazine (352) resulted from the... 

To corroborate the proposed mechanism, the catalytic reductive aldol coupling of acrolein with phenyl glyoxal monohydrate was performed under 1 atmos. elemental deuterium. Exposure of the aldol product to excess hydrazine in situ results in formation of the pyridazine, which incorporates precisely one deuterium atom in a manner consistent with the general mechanism proposed in Scheme 22.4 (Scheme 22.9). 

The electroreductive hydrogenation of pyridazine-3-ones performed at the first wave, in acidic or basic medium, takes place at the 4,5-double bond. A further reduction of 4,5- dihydropyridazin-3-ones in basic media, affords the corresponding tetrahydro derivatives (Scheme 139) [252]. 

Perhydropyrido[l,2-6]pyridazine was prepared from perhydropyrido [l,2-fc]pyridazin-2-one by reduction with LAH (65MI1, 65URP170506 66KGS91 78JA4012), and from 4,4a,5,6,7,8-hexahydro-3//-pyrido[l,2-b] pyridazine by catalytic reduction over Pt02 in acetic acid (68YZ216). Re-... 

Reduction of 2-methyl-4-phenyl-3//-pyrido[l,2-Z)]pyridazin-3-one (44) with NaBH4 in ethanol afforded the 5,6,7,8-tetrahydro derivative [76JCS(CC)275 78JOC2892],... 

Dicobalt species have also been shown to result in cobalt s possessing characteristically unstable oxidation states. A binary cofacial dicobalt porphyrin species has been shown to undergo a pair of one-electron oxidation steps as well as a pair of one-electron reduction steps [49] the two cobalt centers behave essentially independently of one another, so that mixed-valence complexes can be generated. Brooker and coworkers [50] investigated a pyridazine Schiff-base macrocycle with two cobalt centers (4), each of which could undergo a separate one-electron oxidation or reduction to produce a species capable of existing in five different combinations of redox states. Most interesting about this complex is the formation of cobalt... 

Yutilov et al. reported the formation of the [l,2,3]triazolo[4,5- / pyridazin-4-one ring system with simultaneous conversion of the 7-nitro into a methyl substituent, and reduction of the aryl nitro group to an amino substituent on... 

Similar saturation of a C=N bond is found in the reduction (pH 4.5 or 9) of 3-methoxycarbonyl-5-methylfuro[2,3-d]pyridazin-4-one.398... 

In the course of probing the range of reactivity accessible to decamethyl-samarocene, substrates containing C=N double bonds as part of 6-membered heterocycles have been tested. In the reaction with pyridazine reductive carbon-carbon bond formation occurred (compare Sect. 3.2) [99], The coupled ligand bridges two Sm(III) centers via the four nitrogen positions. In the phenazine reaction one phenazine ligand is placed between the Sm(III) centers (Fig. 20 Table 16) [203]. 

Diazoninones 64 were synthesized by reduction of hexahydro-l//-pyrazolo[l,2-tf]pyridazin-l-ones with sodium in liquid ammonia (Scheme 7, Section 14.10.5.2.1) <2000CL1104, 2002T7177>. One of the synthetic routes for the preparation of diazoninone 291 includes reduction of dihydropyrimidinone 292 (Scheme 53) <2002T7177>. 

Reduction of pyridazin-4-ones seems not to have been reported, f. Derivatives of Cinnoline. 3-Hydroxycinnoline (222)44 is reduced in a two-electron wave from pH 0 to 11. In strongly acid solution the main product is 1-aminooxindole (223), which is also obtained on reduction with zinc and sulfuric acid.232 Reduction in an emulsion of an aqueous phosphate buffer (pH 6.5) and n-butanol produced a nearly quantitative yield of 3-keto-l,2,3,4-tetrahydrocinnoline (224) this compound was easily reoxidized to 3-hydroxycinnoline. 

In addition to the foregoing 1,4-difunctional compounds used for cyclizations, the following have been used to give pyridazines or theirreduced analogs , 4-hydroxy ketones, l,4-haloketones, l,4-dibromobutane, 2,5-dibromohexane, 1,4-halo-esters, or butadiene dioxide. Hexahydropyridazine results as one of the oxidation products of 1,4-diaminobutane and its 1-butyl analog is formed in the reduction of iV-nitroso-4-chloro-dibutylamine. ... 

Phenacylpyridinium methiodide, when treated with hydrazine under WolfF-Kishner reduction conditions, is transformed into 6-phenyl-4-propylpyridazine. Some related pyridazines were prepared in a similar manner, but 3-benzoylpyridinium methiodide failed to react [80JCS(P1)72]. 2-Dimethylamino-5-phenyl-l, 3,4-thiadiazin-6-one reacts with the electron-rich 1-diethylaminopropyne to give two pyridazines, 49 and 50, in 72% and 2% yield, respectively. The formation of both compounds is explained by the initial addition of ynamine, ring opening, and cyclization in two ways (82CC1003). 

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