Diacyl hydrazines

Diboran reduziert offenkettige 1,2-Diacyl-hydrazine in Bis-[2-methoxy-athyl]-ather auch mit 50%igem OberschuB erst bei 130-135° in guten Ausbeuten zu den entsprechen-den 1,2-Dialkyl-hydrazinen. Als Nebenreaktion kann die Spaltung der N,N-Bindung auftreten (s. S. 484). 

Dialkyl- 1,2-diacyl-hydrazine, selbst Benzoyl-Derivate, lassen sich dagegen bereits in siedendemTHFgutzu den Tetraalkyl-hydrazinenreduzieren. In geringemUmfang konnen sich auch Monoacyl-hydrazine und Amine bilden. So erhalt man z. B. aus 1,2-Dimethyl- 1,2-dipropanoyl-hydrazin neben 82% d.Th. 1,2-Dimethyl-1,2-dipropyl-hydrazin 14% d.Th. 1,2-Dimethyl-2-propyl-l-propanoyl-hydrazin1 bzw. aus 1,2-Dimethyl-1,2-di-benzoyl-hydrazin neben 60% d.Th. 1,2-Dimethyl-1,2-dibenzyl-hydrazin 28% d.Th. Methyl-benzyl- amin1. 

Disubstituted tetrazoles are conveniently prepared from acyl hydrazines (98) and diazonium salts.166 The reaction proceeds through the intermediate tetrazenes (99) followed by cyclization to the tetrazole (100) (Scheme 13). The intermediate can be isolated under mildly basic conditions. Symmetrically 1,2-diacylated hydrazines yield 1-substituted tetrazoles through the elimination of one of the acyl groups.166 - 168 Diformyl-hydrazine is a very convenient starting material for 1-substituted tetrazoles.166, Unsymmetrically 1,2-diacylated hydrazine usually results in mixtures.169... 

Diacetoxyscirpenol (DAS) immunoassay, 14 144-147 Diacetyl, 23 483 Diacetyl control, 10 293 Diacetyl peroxide, 1 148 Diacetyl rest, in beer making, 3 584 Diacrylamide, 1 293 Diacylglycerols, 10 802 Diacyl hydrazines, 13 599 Diacyl peroxides, 14 281 18 467 decomposition of, 18 473 as free-radical initiators, 14 282-284 hydrolysis and perhydrolysis of, 18 466, 473 preparation of, 18 476 properties of, 18 468-469t reaction with amines, 18 474 reduction of, 18 474 symmetrical or unsymmetrical, 18 477... 

Aqueous NaOH (40%, 1.4 mol) is added with stirring at room temperature to the acyl-hydrazine (0.15 mol) and TEBA-C1 (0.5 g, 2.2 mol) in CHC13 (75 ml, 0.95 mol). The mixture is refluxed for 30 min and then poured into ice-water (150 g). The reaction mixture is neutralized at 0°C with cone. HC1 and the organic phase is separated from the precipitate. The aqueous phase and precipitate are extracted with CH2C12 (3 x 50 ml) and the combined organic solutions are dried (MgS04) and evaporated to give the diacyl-hydrazines. 

Auch mit anderen Silylierungs-Reagenzien wurden 1,2-Diacyl-hydrazine zu 1,3,4-Oxadiazolen cyclisiert360,361. 

T) mit Hexamel hylsilazan358 4,67 g (29 mmol) Hexamethylsilizan, 16mmol 1,2-Diacyl-hydrazin und 5,04 g (16 mmol) Tetrabutylammonium-fluorid-Tris-hydrat erhitzt man 21 -48 h unter Stiekstoff zum Sie-den. Nach Destination oder durch Umkristallisation erhalt man die 2,5-disubstituierten 1,3,4-Oxadiazole Ausbeute 63-81%. 

Nicht immer ist eine Isolierung der 1,2-Diacyl-hydrazine notwendig, sondern die Dehy-dratisierungkann ausgehend von Monoacyl-hydrazinen und Carbonsauren bzw. Carbonsaure-Derivaten z.B. Carbonsaure-chloriden330,369 in einem Reaktionsschritt meist ohne Ausbeute-verlust erreicht werden. 

LaCtman auf l,2-Bis-[l-imino-alkyl]-hydrazine salpctrige Saure einwirken, erfolgt unter Stick-stoff-Eliminierung Cyclisierung zu 2,5-disubstituierten 1,3,4-Oxadiazolen472. Die Reak-tion verlauft iiber 1,2-Diacyl-hydrazine. 

Zirconium(IV) forms a rather large number of complexes with ONO- and ONS-tridentate Schiff base ligands, ONNO- and SNNS-tetradentate Schiff base ligands, and related species such as diacyl hydrazines. Relatively few hafnium analogues have been reported thus far. 

However, acylation reactions of N-unsubstituted pyrazolines with halogen anhydrides of acids are very often followed by the destruction of the heterocyclic ring owing to the ease of breaking the C(5)—Nq) bond located at the (3-position of the azomethine group [140, 141, 142, 166]. For example, pyrazoline 108 treated with halogen anhydrides of acids yields a,(3-unsaturated ketone 109 and diacyl-hydrazine 110 [166] (Scheme 2.29). 

A number of ferrocene-containing 1,3,4-oxadiazoIes have been prepared. The reaction of ferrocenecarboxhydrazide with triethyl orthoformate gave three products, the principal one being 2-ferro-cenyl-l,3,4-oxadiazole (126 R = H). 76 2-Phenyl-5-ferrocenyl-l,3,4-oxadiazole (126 R = CgH5) and 2,5-diferrocenyl-l,3,4-oxadiazole (126 R = ferrocenyl) were prepared from the appropriate 1,2-diacyl-hydrazines.117 A number of other ferrocenyloxadiazoles, including the bis compound 127, were prepared in a similar manner.117 The oxadi-... 

It remains to be clarified why the 1,2-diacylated hydrazine B and not the 1,1-diacylated hydrazine D is formed in the hydrazinolysis of Figure 6.20. In the intermediate C the only nucleophilic electron pair resides in the NH2 group and not in the NH group because the electron pair of the NH group is involved in the hydrazide resonance C —> C and is therefore not... 

The preparation of the symmetrical diacyl hydrazine derivatives, (I), is described (4). 

Pyridazin Hexahydro- E16a, 523 (Diacyl-hydrazin-Hydrier.)... 

Azo-ene reactions. The ene reaction provides a powerful method for C-C bond formation with concomitant activation of an allylic C-H bond. A variety of functionalized carbon skeletons can be constructed due to the range of enophiles which can be used. For example, carbonyl compounds give homoallylic alcohols and imino derivatives of aldehydes afford homoallylic amines. The azo-ene reaction offers a method for effecting allylic amination by treatment of an alkene with an azo-diester to afford a diacyl hydrazine which upon N-N cleavage furnishes a carbamate. Subsequent hydrolysis of the carbamate provides an allylic amine. Use of chiral diazenedicarboxylates provides a method for effecting stereoselective electrophilic amination. 

High-level ab initio calculations show that diacyl-hydrazines are intrinsically nonplanar with respect to the CO—N—N—CO torsion, and the corresponding rotational barriers are high.171 The global minimum finds the nitrogen lone pairs approximately perpendicular to one another. Thus, their conformational properties are essentially determined by the conformation of their hydrazine and urea constituents. As a result of restricted rotation about the N—N bond, azapeptides cannot adopt extended conformations. This is likely the reason that they are resistant172 to chymotrypsin-like proteases, which bind their substrates in extended forms. 

Triazoles are available via cyclodehydration reactions of iV,iV -diacyl-hydrazines with amines, although the conditions are often quite vigorous. An interesting variant utilises i ym-triazine (1,3,5-triazine) as an equivalent of HN(CHO)2. Condensations of aminoguanidine with esters, or an orthoformate, give 3-amino-l,2,4-triazoles. ... 

Oxadiazoles are available by cyclodehydration of iV,iV -diacyl-hydrazines or their equivalents,... 

Thiadiazoles are available by a nnmber of convenient general rontes inclnding cycUsation of N,N -diacyl-hydrazines, or 1,3,4-oxadiazoles, with phosphorus sulfides. 2-Amino-l,3,4-thiadiazoles are prepared via acylation of thiosemicarbazides and the parent compound is easily obtained from hydrogen sulfide and dimethylformamide azine. °... 

Reaction of carboxylic esters with hydrazines is generally easier than that with amines. Simple aliphatic esters often give the corresponding hydrazide exothermally at room temperature, though it is advisable to warm the mixture on the water-bath for a short time thereafter. In such reactions the formation of 1,2-diacylated hydrazines rarely proves troublesome although it is a frequent side reaction when acid chlorides or anhydrides are used. The following details exemplify the technique ... 

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