Hydrazine to give

Acid hjdrazides from esters. Meth and ethyl esters react with hydrazine to give acid hydrazides ... 

Ethyl-N-(2 thiazolyl)carbainate reacts with aqueous hydrazine to give 271 (Scheme 165) (263). 

From Hydrazines and P-Bifunctional Compounds. One of the oldest examples in this class is the reaction of a p-diketone with a substituted hydrazine to give a pyrazole (eq. 1). 

AK(30)26l). 2-Acetoxyfuran-3(2i/)-ones react with hydrazine to give 3,6-disubstituted-4-ethoxycarbonylpyridazin-4(li/)-ones (184) as the main product, but with mono-substituted hydrazines in addition to these pyridazines anhydro-5-hydroxypyridazinium hydroxide (185) derivatives and some pyrazole derivatives are also formed (Scheme 102) (79JOC3053). The... 

The most useful syntheses of pyridazines and their alkyl and other derivatives begins with the reaction between maleic anhydride and hydrazine to give maleic hydrazide. This is further transformed into 3,6-dichloropyridazine which is amenable to nucleophilic substitution of one or both halogen atoms alternatively, the halogen(s) can be replaced by hydrogen as shown in Scheme 110. In this manner a great number of pyridazine derivatives are prepared. 

Uracil reacts with hydrazine to give pyrazol-3(2if)-one (944) and urea N-methyl- and dimethyl-hydrazine behave similarly to give the 2-methyl- and 1,2-dimethyl derivatives. The reactions of hydrazines with uridine and related nucleosides and nucleotides is well studied (67JCS(C)1528). The tautomerism and predominant form of uracil are discussed in Section 2.13.1.8.4. 

In the 2-position, the methylthio derivatives have mostly been used, especially in the synthesis of piromidic acid, pipemidic acid and their analogues, whilst in the tricyclic series the methylthio derivative (96) was reacted with hydrazine to give the versatile intermediate (97) (79JHC707). 

The only other synthesis of a benzo fused derivative involves the pyridazino[4,3-cjisoquinoline series, the isoquinoline derivative (377) reacting with hydrazine to give (378) (74YZ607), although an s-triazolo-fused pyrido[2,3-tf Ipyridazine was obtained in the reaction of l-amino-3-iminoisoindolenine with hydrazine and formic acid (56GEP951993). 

The imonium salt (199), obtained from ynamines and phosgeneimonium chloVide, underwent ready reaction with monosubstituted hydrazines to give the 3,5-bis(dimethyl-amino)pyrazole (200) (68T4217, 69T3453). Similarly, the adduct (201), resulting from the addition of phosgene to ynamines, likewise reacted with sym-disubstituted hydrazines to give pyrazoles (202). With hydroxylamine derivatives the isoxazolinone (203) was obtained. 

To form a five-membered ring in this manner, the 1,3-bielectrophile must contain a heteroatom, and several systems such as the aza analog of (204) are known (68T4217,69T3453). Dimethyl AA-ethoxycarbonylthiocarbonimidate (209) reacted readily with a monosubstituted hydrazine to give the 1,2,4-triazolinone (210), and with hydroxylamine the 1,2,4-oxadiazolinone (211) was obtained (73JCS(P1)2644). 

Perhaps the greatest utility of (36-39) (and many of their precursors, such as 41, 42 and 48) is as starting points for the synthesis of highly functionalized cyclohexanes. For example, (38) has been converted in five steps (overall yield 70-75%) to streptamine (57) the key step is selective ring-opening with hydrazine to give intermediate (56) (75AG(E)630). 

Polyfluoroalkyl fluorosulfates react with substituted hydrazines to give the corresponding polyfluorocarboxylic hydrazides [90] (equation 78)... 

An aldehyde or ketone 1 can react with hydrazine to give a hydrazone 2. The latter can be converted to a hydrocarbon—the methylene derivative 3—by loss of Na upon heating in the presence of base. This deoxygenation method is called the Wolff-Kishner reduction. ... 

Azelastine (107) is an antiallergic/antiasthmatic agent prepared from 4-chlorobenzyl-2 -car-boxyphenylketCHie (105) by condensation with hydrazine to give the phthalazinone (106) followed by reaction of the sodium salt of this last with 2-(2-chloroethyl)-N-methylpyrrolidine (presumably involving nucleophilic ring expansion of the bicyclic quaternary salt putatively formed as a first product) to complete the synthesis [30]. 

In initial steps, 2-nitrobenzylbromide and cyclohexylmethylamine are reacted and that initial product reacted with hydrazine to give N-(2-aminoben2yl)-N-methyl-cyclohexylamlne. 

Triarylpyrylium salts react with hydrazine to give 4//-l,2-diazepines 472-1°s,ioo vja g unstable intermediates 3.110 The reaction fails with pyrylium salts containing alkyl groups in positions 2 and 6, with the exception of 2,4,6-tri-tert-butylpyrylium perchlorate. In some cases it is advantageous to use a thiapyrylium salt in place of the pyrylium salt. Selected examples are given. 

The diketone 1 reacts with hydrazine to give the 5/7-2,3-benzodiazepine 2.127... 

An illustrative example of the Michael reaction is that of the thiirene dioxide 19b with either hydroxylamine or hydrazine to give desoxybenzoin oxime (87) and desoxybenzoin azine (88), respectively, in good yields6 (see equation 29). The results were interpreted in terms of an initial nucleophilic addition to the a, j8-unsaturated sulfone system, followed by loss of sulfur dioxide and tautomerization. Interestingly, the treatment of the corresponding thiirene oxide (18a) with hydroxylamine also afforded 86 (as well as the dioxime of benzoin), albeit in a lower yield, but apparently via the same mechanistic pathway6. 

Condensation of phenylalaninenitrile, prepared from phenyl acetaldehyde, with 1-oxime of pyruvaldehyde afforded the pyrazine N-oxide, which was further rearranged to give the N-acetyl pyrazinone. The acetyl groups were removed by treatment with hydrazine to give the target 6-aminopyrazinone. 

Treatment with hydrazine to give the hydrazone and then CuBr2/f-BuOLi generated the gem-dibromide. " Oximes gives gem-dichlorides upon treatment with chlorine and BF3-OEt2, and then HCl. Some dithianes can be converted to gem-... 

The pyrazoles 51 react with triethyl orthoformate and hydrazine to give the pyrazolopyrimidines 52 which react further with acetic anhydride and benzoyl chloride to give pyrazolotriazolopyrimidines 53 and with a-ketohydrazonoyl halides to give pyrazolopyrimidotriazines 54 <95MI01 96CA(124)86924>. 

This product was cyclized by AA -bis(trimethylsilyl)hydrazine to give (4) ... 

The coupling of enals and glyoxals was realized by hydrogen-mediated reaction with the cationic Rh complex and PI13P [35]. The intermediate aldehyde enolates derived via Rh-catalyzed hydrogenation were trapped with glyoxals to form (l-hydroxy-y-kclo-aldchydes, which were treated sequentially with hydrazine to give pyridazines in a one-pot transformation to provide, for example, a 62% yield of 72 (Scheme 21). 

Alkoxycarbonylimidazoles or alkoxythiocarbonylimidazoles, easily prepared from alcohols and CDI or ImCSIm, are treated with hydrazines to give alkoxycarbonic acid hydrazides and thiohydrazides, respectively 12261,12271... 

Parallel array synthesis was used to access the 3-aryl-tetrahydro-l,2-diazepines 90 (and other related compounds) by cyclisation of the chloro ketones 88 on reaction with hydrazine to give 89 followed by sulfonamide formation the Si-TrisAmine was added at the end as a scavenger to remove any unreacted arylsulfonyl chloride remaining <06MCL3777>. 

Thermal cyclization of 254 afforded 255, which reacted with hydrazine to give 256. Heating a suspension of 256 in DMF gave 6,10-dihydro-6//-pyrido[3, 2 5,6]pyrimido[2,1 -c] [ 1,2,4]triazin-5-one 259 via the intermediates 257 and 258 (86JHC509). 

This ring system was prepared by the alkylation of [ 1,4]benzothiazinone with ethyl bromoacetate followed by reaction with Lawesson s reagent and cyclization with hydrazine to give the thia analogue of 503 (91MI6). 

Treating 644 with triethyl orthoformate gave l,2-dihydro-l-oxo[l,2,4]-triazino[4,5-a]indole 648, whose reaction with phosphorus oxychloride or phosphorus pentasulfide gave 650 and 649, respectively. Both reacted with hydrazine to give 651, which then was converted into [l,2,4]triazolo[3, 4 -/][1,2,4]triazino[4,5-a]indoles 652 and 653 by reaction with formic or acetic acid, respectively (80JHC77). 

Table 42 Reaction of fluorinated 1,2,4-oxadiazoles with hydrazine to give 1,2,4-triazole derivatives...

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