Phenylhydrazone derivatives, formation

An example of the electrophilic reactivity of the C-4 atom is the easy formation of oxime and phenylhydrazone derivatives (422). It has been reported, however, that 2 pheny -A-2-thiazoline-4-one does not react with phenylhydrazine (397). 

The triazino-oxathiazines 559 were prepared by cyclocondensation of phenylhydrazone derivatives 558 with chlorosulfonyl isocyanate. The formation of 559 was dependent on the substituents (9ISC 1695). 

CR(Q(262)1017>. The nucleophilic reactivity of the oxygen atom has been observed in the acetylation by acetic anhydride of 2-aryl- and 2-heteryl-A2-thiazolin-4-ones (Scheme 136). 2-Alkoxy and 2-methyl derivatives of A2-thiazolin-4-one (196) react with OPCl3 to yield thiazolylphosphoric esters (197) which have insecticidal uses (Scheme 137). An example of the electrophilic reactivity of the C-4 atom is the easy formation of oxime and phenylhydrazone derivatives. 5-Aryl-A2-thiazolin-4-one (198) gives the 1,3-dipolar cycloaddition product (199) with methyl fumarate and methyl maleate (Scheme 138). Under similar conditions, treatment of (198) with dimethyl acetylenedicarboxylate (DMAD) yields a thiophene derivative (202) when R = Ph and a pyridone derivative (203) when R = H (Scheme 139). The proposed mechanism involves the formation of a mesoionic intermediate (200) which reacts in a cycloaddition with a second molecule of DMAD, yielding (201), the decomposition of which depends on the R substituent. 

Phenylhydrazones exhibit another mode of reaction (Scheme 65). The reaction of butadiene with the phenylhydrazone of acetaldehyde 204 (1 mol % (Ph3P)4Pd, THF, 110 °C, 24 h) affords a 2 1 mixture of 205 and 206 (86%). A small amount of the protic (H—Y) trapping prodnct was also observed. The formation of 205 can be rationalized by addition of the phenylhydrazone in the fashion of a R (R )C=Y-type electrophile to a palladacycle in an Sgs fashion to 208 followed by hydride transfer to 209. Rednctive elimination conld acconnt for the formation of 205. Thns, 206 could be formed via a similar pathway, by addition of the phenylhydrazone in an rather than fashion. The proposed hydride transfer invoked to rationalize the formation of the observed products offers interesting possibilities and appears worthy of further investigation. Phenylhydrazones derived from propanal, acetone, and methyl ethyl ketone behave similarly (60-95% yield), although the ratio of 205/206 and the proportion of the protic (H—Y-type) trapping product vary. 

We recall that hydrazine and 2,4-dinitrophenylhydrazine react with carbonyl compounds to give hydrazones. However, monosaccharides do not give simple phenylhydrazone derivatives. After the initial formation of a phenylhydrazone, further reaction occurs to give the osazone, which has two molecules of phenylhydrazine incorporated into it. 

Reductive cleavage of phenylhydrazones of carbonyl compounds provides a route to amines. The reduction is carried out conveniently in ethanol containing ammonia over palladium-on-carbon. Ammonia is used to minimize formation of secondary amines, derived by addition of the initially formed amine to the starting material (160). Alternatively, a two-phase system of benzene, cyclohexane, toluene, or dioxane and aqueous hydrochloric acid can be used. 

About the same time a number of publications appeared on the complete synthesis of 7a, 7b, 30 and 31 using a different approach to build the alkaloid framework (Scheme 5 68M1364, 68M1584, 69JCA(C)2738). Phenylhydrazone 34 under Fischer reaction conditions was converted into indole 34a with subsequent successive transformations to pentacyclic derivative 35. Its acid-initiated rearrangement led to the formation of 7b and 30 in a ratio of 1 5. While 7b and... 

The base-catalyzed, / -elimination reaction of D-mannose phenyl-hydrazone is consistent with the acyclic structure for the phenylhydra-zone in solution. However, the small proportion of a nitroxide radical observed on treatment of the phenylhydrazone with a strong base may indicate the existence also of a fractional proportion in a cyclic structure in equilibrium with the open-ring structure, as was suggested by Blair and Roberts (43). The hydrazino moiety required for nitroxide-radical formation could be derived from the cyclic form of D-mannose phenylhydrazone in solution. 

The H NMR spectra of the pyrano[3,2-< ]pteridine (341) and its enantiomer derived from the phenylhydrazone of D-arabinose (343) show a time-dependent change due to the formation of an equilibrium involving the isomeric furo[3,2- ]-pteridines. Analogous results were obtained with 5,6-diamino-3-methyl-2-methylthio- and 5,6-diamino-2-methylthio-4(3//)-pyrimidone (342), respectively, leading in the latter case even to a separation of the two enantiomers (344) and (345) with respect to the chiral centers at the 6- and 7-position of the pteridine moiety (Equation (15)). 

The formation of the pyridinol is prevented if, in the step 19 to 20, no anion can be eliminated from C-3 this is the case with 5-amino-3,5-dideoxy-l,2-0-isopropylidene-a-D-er /thro-pentofuranose, which, on acid hydrolysis, afFords only the Amadori rearrangement product and no pyridine derivative. The reaction then proceeds, according to the above mechanism, in only one direction from 19. The 3-deoxypentose is prepared, in a manner analogous to the formation of 15, from 3-deoxy-l,2-0-isopropylidene-a-D-riho-hexofuranose through catalytic reduction of the phenylhydrazone of its periodate-oxidation product. ... 

Cyclohexanone phenylhydrazone undergoes cyclization to 1,2,3,4-tetrahydro-carbazole with such ease that formation and cyclization of the derivative can be combined into one step with acetic acid as catalyst and solvent. A mixture of 1 mole of cyclohexanone and 360 g. of acetic acid is stirred under reflux and 1 mole of phenylhydrazine is added during 1 hr. After refluxing, the mixture is worked... 

Both N-N and N-C bond fission occurs on irradiation of the hydrazone derivatives (191). The photodegradation of the phenylhydrazone and the hydrazone of benzil have also been described. a-Ketoiminyl radicals are formed on irradiation of oximino ketones at low temperature. A study of the photochemical decomposition of sulfamic esters and their use as initiators of cross-linking of a melamine resin have been described. The bispyridinyl radical (192) is formed by one electron reduction of the corresponding pyridinium salts. The irradiation of this biradical at 77 K results in C-N bond fission with the formation of benzene-1,3-diyl. The predominant products from the irradiation (X,> 340 nm) of (193) in methanol were identified as A -hydroxy-2-pyridone and (194) from the fission of the C-O bond. Other products were 2-pyridone, (195) and (196) that arise from O-N bond fission. The reaction is to some extent substituent dependent and a detailed analysis of the reaction systems has identified an intramolecular exciplex as the key intermediate in the C-O bond heterolysis. 

New examples of base- or acid-induced ring contraction of pyridazines include the formation of azoles. An investigation of the known cyclization of the phenylhydrazone of ethyl levulinate to pyridazinone revealed that in the presence of BF3-etherate the corresponding indole derivative (262) is obtained. The latter is formed also from the pyridazinone and ethanolic hydrogen chloride. 5-Phenylpyridazinone-4-oxime, when treated with zinc in acetic acid, is rearranged to the pyrrole 263. ... 

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