Hydrazones chelated structures

Acyl-, 4-alkoxycarbonyl- and 4-phenylazo-pyrazolin-5-ones present the possibility of a fourth tautomer with an exocyclic double bond and a chelated structure. The molecular structure of (138) has been determined by X-ray crystallography (Table 5). It was shown that the hydroxy group participates in an intramolecular hydrogen bond with the carbonyl oxygen atom of the ethoxycarbonyl group at position 4 (8OCSCII21). On the other hand, the fourth isomer is the most stable in 4-phenylazopyrazolones (139), a chelated phenyl-hydrazone structure. 

Concerning l-phenylazo-2-naphthol and 1,2-naphthoquinone 2-phenyl-hydrazone, the chelate structure of which can be influenced by the solvent, reference is made to the work of Burawoy and coworkers. ... 

Of the four chelated structures suggested by the Fiesers, the resonance pair A and B suffice to explain the fact that only the hydrazone residue at C-1 can be methylated or benzoylated, because the imino group of the hydrazone residue at C-2 is involved in hydrogen bonding, Structures C and D would be expected to undergo alkylation on the hydrazone residue at C-2 and must, therefore, either be eliminated from consideration or be regarded as minor constituents. This leaves the resonance pair A and B as the most probable of the Fiesers structures. 

Further applications can be mentioned briefly. SAMP was used in the resolution of 4-demethoxy-7-deoxydaunomycinone/ in ee determinations (Scheme 1), as a chelate for tetracarbonylmolybdenum complexes/ in intramolecular Heck reactions, as polysilylated hydrazine, in the enantioselective synthesis of isoquinuclidines, and in the conversion of hydrazones to aldehydes and nitriles. The structure of a chiral lithium SAMP hydrazone azaenolate has been determined. In cases where SAMP did not lead to satisfactory inductions, a modified auxiliary, (S)-l-amino-2-dimethylmethoxymethylpyrrolidine (SADP), enhanced the stereochemical control. 

Enders, D., Bachstaedter, G., Kremer, K. A. M., Marsch, M., Harms, K., Boche, G. The structure of a chiral lithium azaenolate monomeric intramolecular chelated lithio-2-acetylnaphthalene-SAMP-hydrazone. Angew. Chem., Int. Ed. Engl. 1988, 27,1522-1524. 

The structure of inosose mono(phenylhydrazones) is quite similar to that of acyclic saccharide hydrazones neither possess chelated rings and both exist in the Schiff-base form. Cyclization to hydrazino forms, a common process among many saccharide hydrazones, has not been observed in inosose hydrazones, probably because the resulting bicyclic compounds would be unduly strained or rigid. 

Reactions of cyclic and acyclic 1,2,3-triones with phenylhydrazine give rise to mono- and bis-(phenylhydrazones). The central carbonyl group of a vicinal tricarbonyl system is electron-deficient and highly electrophilic,255 which is why treatment with an aryldiazonium ion affords 2-phenylhydrazones. The structure of such bis(phenylhydrazones) as cyclopentane-1,2,3-trione 1,3-bis(phenylhydrazone), dehydroascorbic acid 2,3-bis(phenylhydrazone), and cy-clobutanetetraone l,3-bis(phenylhydrazone) has been studied by UV, IR,1H-, 13C-, and 15N-NMR spectroscopy.265-268 Quantum-mechanical calculations to predict the most stable tautomeric forms of some 1,2- and l,3-bis(phenylhydrazones) revealed that the chelated bis(hydrazone) structure was usually more stable than the azoene-hydrazine structure.269-271 This does not mean that such structures do not exist, for example cyclobutanetetraone l,2,3-tris(phenylhydrazone) exists in a stable phenylazoene-hydrazine structure (see 49 Scheme 8).257-263... 

More recently, Enders group has described the X-ray crystal structure of the chiral hydrazone anion (19). This internally chelated chiral hydrazone crystallizes as the bis(tetrahydrofuran) monomeric adduct. The lithium in this structure is 17° out of the C—C— N plane and is predominantly associated with the anionic nitrogen (and the chelating methoxy group). Interactions with the =CH2 carbon are minimal. Earlier studies by Bauer and Seebach had examined the association behavior of (19). They found that in THF this azaallyllithium reagent was monomeric. While there is no or ri -interaction with the azaallyl anion, the lithium in this structure is tetracoordinate and prochiral. Preferential coordination of lithium to an electrophile such as a carbonyl oxygen with selective replacement of one THF moiety could be involved in some of the asymmetric aldol reactions discussed below. 

The authors favored the azafulvene structure 1057 for the product, since they observed a chelated enolic hydroxyl group in the IR spectrum. In addition, the product gave a positive ferric chloride test but did not afford an oxime or a hydrazone. Finally, the NMR spectmm was more consistent with 1057 than with 1056. 

For example, meso-tetraaryltetrabenzoporphyrin zinc complex results from heat treatment of the corresponding 3-benzylidenisoindolinone with zinc benzoate l Appropriately substituted methine and azomethine isoindolinones featuring substructure 24 were also converted into stable metal chelate pigments of general structure 26 via a metal template reaction with aromatic and heterocyclic a-hydroxy aldehyde or ketone hydrazone derivatives incorporating the structural element 25 . ... 

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