Hydrazones proton

According to a detailed mechanistic study, the first step is the abstraction of the relatively acidic hydrazone proton (93- 97). This is followed by hydride attack on the trigonal carbon of the C=N bond, mainly from the a-side at C-3, together with the concomitant loss of the tosylate anion (97 -> 98). Expulsion of nitrogen from the resulting intermediate (98) yields a fairly insoluble anion-metal complex (99) which upon decomposition with water provides the methylene derivative (100). 

A mechanism which is consistent with the various experimental results for olefin formation involves the initial abstraction of the hydrazone proton (103->106) In this case, however, expulsion of the tosylate anion is associated with the abstraction of a second hydrogen from C-16 instead of hydride attack on the C=N bond (compare 97 98 and 106 107). Ex-... 

Thus, the reduction of tosylhydrazones with sodium borodeuteride in dioxane provides only monodeuterated analogs. For the insertion of two deuteriums it is necessary to first exchange the hydrazone proton and to carry out the reduction in aprotic or deuterated solvents. Under these conditions the reduction of the tosylhydrazone derivatives of 7- and 20-keto... 

A mechanism which is consistent with the various experimental results for olefin formation involves the initial abstraction of the hydrazone proton (103 - 106)82 In this case, however, expulsion of the tosylate anion is associated with the abstraction of a second hydrogen from C-16 instead of hydride attack on the C=N bond (compare 97 - 98 and 106 - 107). Expulsion of nitrogen from the resulting intermediate (107) yields an anion (108) which is most probably stabilized in the form of a metal complex and can be readily decomposed by water to give an olefin (109). This implies that 17-d1-androst-16-ene (104) can be prepared by using deuterium oxide as the sole deuterated reagent.82... 

Monoanions of the ligands (46 for X = NH), formed by loss of the hydrazone proton, produce neutral molecules [Mn(N3)2]° four of these species have been described, and despite an earlier report to the contrary,148 they are all high spin.144... 

A large number of Brpnsted and Lewis acid catalysts have been employed in the Fischer indole synthesis. Only a few have been found to be sufficiently useful for general use. It is worth noting that some Fischer indolizations are unsuccessful simply due to the sensitivity of the reaction intermediates or products under acidic conditions. In many such cases the thermal indolization process may be of use if the reaction intermediates or products are thermally stable (vide infra). If the products (intermediates) are labile to either thermal or acidic conditions, the use of pyridine chloride in pyridine or biphasic conditions are employed. The general mechanism for the acid catalyzed reaction is believed to be facilitated by the equilibrium between the aryl-hydrazone 13 (R = FF or Lewis acid) and the ene-hydrazine tautomer 14, presumably stabilizing the latter intermediate 14 by either protonation or complex formation (i.e. Lewis acid) at the more basic nitrogen atom (i.e. the 2-nitrogen atom in the arylhydrazone) is important. 

DCCI reacts with hydrazone derivatives or with the thiourea 83 to give nitrogen ylides such as 84 and hence by protonation 3-aminotriazolopyridines (88CC506, 93JCS(P1)705). A solution of iodine in pyridine reacts with propional... 

The hydrazone structure 40 can be eliminated at once many examples of this class of compounds are known and their properties are completely different from the diaziridines. For example, 3,3-dimethyldiaziridine has a heat of combustion of about 35 kcal higher than the isomeric acetone hydrazone. Further pairs of isomers of diaziridines and hydrazones are known. The spectrum eliminates both the hydrazone structure and the betaine structure 41. The diaziridines do not absorb in the UV range. In the infrared spectrum, absorption is completely absent in the double-bond region. - The NMR spectrum of 3,3-dimethyldiaziridine is in agreement with a formulation that has two equivalent iV-protons. ... 

Base abstracts a weakly acidic N-H proton, yielding a hydrazone anion. This anion has a resonance form that places the negative charge on carbon and the double bond between nitrogens. 

Protonation of the hydrazone anion takes place on carbon to yield a neutral intermediate. 

There are also some couplings in which hydrazones are formed but for which the azo tautomer is not detectable and probably does not exist. This is the case in some coupling reactions involving methyl groups of aromatic heterocycles (see, for example, 12.48 and 12.49 in Sec. 12.5). Replacement of a methyl proton by an arylazo group (Scheme 12-3) would result in an azo compound containing an sp3-hybridized — CH2 — group (12.1). The latter is less stable than the tautomeric hydrazone (12.2), in which there is a n-n orbital overlap from the heteroaromatic to the aromatic system. 

As seen from (Scheme 12-73) the primary product of arylazo substitution is the anion Ar - N2 - R . It is protonated in a subsequent step either at a basic center of the residue R (preferentially at an oxygen atom, for example, in coupling with phenol), or at the azo nitrogen next to the group Ar forming a hydrazone. The problem as to whether the final product is a hydroxyazo- or a quinonehydrazone-type... 

This regiospecificity has been shown to depend on the stereochemistry of the C=N bond in the starting hydrazone. There is evidently a strong preference for abstracting the proton syn to the arenesulfonyl group, probably because this permits chelation with the lithium ion. 

Kasianowicz, J., Benz, R. and McLaughlin, S. (1984). The kinetic mechanism by which CCCP (carbonyl cyanide m-chloro-phenyl-hydrazone) transports protons across membranes, J. Membrane Biol., 82, 179-190. 

The solid-solid transformation of 2-amino-3-hydroxy-6-phenylazopyridine, 57a, to 57b proceeds through two intermediate phases (119). X-Ray and IR studies of the former, low-temperature, and the latter, high-temperature phase show that they are the phenolazo and quinone hydrazone forms, respectively. This solid-state tautomerism can be accounted for by a cooperative intermolecular shift of protons across the various hydrogen bonds. However, because of the complexity of the hydrogen-bond network, the actual pathway of the proton shift has not been uniquely defined. 

In 2-pyrazolines [103] the conjugation involves N-1 and C-3 atoms. 2-Pyrazolines may be regarded as cyclic hydrazones, which have the advantage over non-cyclic products of being stable to hydrolysis. It has been shown by Elguero and Jacquier (1965) that protonation occurs at N-1, giving cation [104], while forms with the proton at N-2 and C-3 [105] may exist in amounts of less than 1-5%. 

Cyclic analogues of hydrazones [151], 2-pyrazolines, show both protonation and alkylation on N-1, as has already been discussed on page 326. The sp nitrogen (which distinguishes these systems from enamines) does not appear to play any direct part. 

Oxidation of chalcone phenylhydrazone 13 leads to a pyrazole and the expelled proton catalyses formation of a pyrazoline from the chalcone phenyl-hydrazone [43]. The latter undergoes further anodic oxidation (p. 308). In the presence of pyridine as a proton acceptor, the pyrazole becomes the major product. A further example of oxidative cyclization is the conversion of a-oximino phenylhydrazones to 1,2,3-triazole-l-oxides 14 [44]. 

Similar chemistry is possible starting from hydrazones bearing acidic a protons an initial diastereoselective enolization and electrophilic functionalization of the hydrazone can be followed by derivatization which is stereoselective in the planar sense . ... 

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