Hydrazone, preparation

The hydrazone prepared above (153 g. 0.42 mol) was heated at reflux for 5 h in 5% H2SO4 (750ml). The solution was cooled to 4 "C and after 12h the precipitate was collected by filtration. Recrystallization from MeOH/water (70 30) gave the product (145 g, 99%). 

Hydrazones prepared from proline derivatives 2 provide an efficient and versatile route to the... 

Hydrazine hydrate, 50, 3 Hydrazoic acid, safe substitute for, 50, 107 HYDRAZONES, PREPARATION, 50,... 

As shown in equation 53, when the zincated hydrazone, prepared from hydrazone by treatment with 2 equivalents of f-butyllithium and zinc(II) bromide, is treated with alkenylborane, the a-borylorganozinc is obtained with high diastereoselectivity. This pseudo-gem-dimetal species reacts with allyl halide stereospecifically. Through the transformation, three stereogenic centers are constructed diastereoselectively77. 

Hydrazones prepared from (S)- l-amino-2-(methoxymethyl)pyrrolidine (242) and acyclic ketones have been shown to undergo deprotonation and alkylation with almost complete asymmetric induction at the a-center (79AG(E)397). The ant alarm pheromone, (+)-(5)-4-methyl-3-heptanone (245), was prepared from the metallated hydrazone of diethyl ketone (243) by alkylation with n-propyl iodide and subsequent cleavage of the crude product via its JV-methyl iodide with acid (Scheme 52). The optical purity of the product was >99%. 

Thus, Ghosez et al. were successful in showing that A,iV-dimethyl hydrazones prepared from a,/3-unsaturated aldehydes react smoothly in normal electron demand Diels-Alder reactions with electron-deficient dienophiles [218, 219]. Most of the more recent applications of such 1-aza-l,3-butadienes are directed towards the synthesis of biologically active aromatic alkaloids and azaanthra-quinones [220-224] a current example is the preparation of eupomatidine alkaloids recently published by Kubo and his coworkers. The tricyclic adduct 3-19 resulting from cycloaddition of naphthoquinone 3-17 and hydrazone 3-18 was easily transformed to eupomatidine-2 3-20 (Fig. 3-6) [225]. 

CHaCiO + H2N.NH2 = CHaCiN.NHa + H2O The compounds formed, called hydrazoneSj can be hydrolyzed by boiling with a dilute acid. In the identification of aldehydes, the physical properties of the hydrazone prepared from the aldehyde and phenylhydrazine, C6H5HN.NH2, are frequently determined. The reaction in this case is analogous to that with hydrazine —... 

Hydrazones prepared by the reaction of aryldiazonium salts with malononitrile (trivially named carbonyl cyanide phenylhydrazones, or CCPs) have been known as uncouplers for many years [114]. Studies on the relationship between physicochemical properties and uncoupling potency have been reported [90, 91], and these show that this relationship is very similar to those for other classes of weakly acidic protonophoric uncouplers. Thus, two of the most potent uncouplers of... 

Hydrazones prepared mechanochemically by Lamaty (Section 3.5) were further Af-alkylated in ball mill [15]. Optimal reaction conditions were grinding of mixture... 

By contrast, very high diastereoselectivities have been observed by the use of chiral hydrazones prepared from the C2 symmetric hydrazine 2,5-dimethyl-pyrrolidin-l-ylamine. The asymmetric induction comes at a price, however The hydrazine is not commercially available, and it cannot be recovered as such following oxidative cleavage from the P-lactam. More readily available, and therefore more expendable, hydrazines are SAMP analogs derived from L-proline. ... 

A novel cyclization of trifluoroacetylated hydrazones, prepared by TFAA treatment of -dialkyl aldehyde hydrazones, was reported by Hojo for the synthesis of 5-trifluoromethylimidazoles (Scheme 36) [50]. Formation of the 4-(trifluoro-methyl) isomers was observed in some cases along with the major 5-(trifluoro-methyl)imidazole products, presumably due to isomerization of trifluoroacetylated hydrazones (Table 2). This isomerization is suggested to be enhanced in the presence of silica gel and the isomeric trifluoroacetylated hydrazones cyclized to give the 4-CF3-imidazoles in refluxing toluene (c.f. Scheme 35). 

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