Hydrazones cyclic

A -Pyrazolines and A -isoxazolines (302 Z = NH, O) are cyclic hydrazones and oximes, respectively. 2-Pyrazolines are quaternized at the 2-position (306 307) (64AHC(. ll). 1,3,4-Oxadiazolines (e.g. 308) are very easily ring-opened (66AHCi7 183). 

Pyrazolidines are cyclic hydrazones and their reactivities are comparable, the main difference being found in the oxidation of pyrazolidines to pyrazolines and pyrazoles. 

However, in some cases azines can be converted to hydrazones by treatment with excess hydrazine and NaOH. Arylhydrazines, especially phenyl, p-nitrophenyl, and 2,4-dinitrophenyl, are used much more often and give the corresponding hydrazones with most aldehydes and ketones.Since these are usually solids, they make excellent derivatives and are commonly employed for this purpose. Cyclic hydrazones are also known, ° as are conjugated hydrazones. a-Hydroxy aldehydes and ketones and ot-dicarbonyl compounds give osazones, in which two adjacent carbons have carbon-nitrogen double bonds ... 

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%. 

To 60 mL absolute EtOH there was added 12.2 g 1-(2,5-dimethoxy-4-chlorophenyl)-2-(phthalimido)ethane and 2.9 mL of 100% hydrazine. The solution was held at reflux for 15 min. After cooling, the cyclic hydrazone by-product was removed by filtration, and the alcoholic mother liquors taken to dryness under vacuum. The residue was distilled at 145-155 °C at 0.05 mm/Hg to give 5.16 g of a clear, colorless oil. This was dissolved in anhydrous Et20 and treated with hydrogen chloride gas, producing 2,5-dimethoxy-4-chlorophenethylamine hydrochloride (2C-C) as white crystals with a mp of 220-221 °C. Anal. (Ci0H 5C12NO2) C,H,N. 

The template method may be extended to derivatives of imines, and hence to the synthesis of cyclic hydrazones. An example of a templated cyclisation leading to a cyclic hydrazone is shown in Fig. 6-13. 

If A-amino nitrogen heterocycles are used as the hydrazine component, cyclic hydrazone dyes are obtained whose absorption maximum is shifted bathochromi-cally with respect to the open-chain hydrazone dyes [38], The dye 15 dyes polyacrylonitrile fibers a clear bluish red shade ... 

In addition to the complexes listed above, the following chelates belonging to the class containing an MN4 unit have been obtained on the basis of l,4-diaza-l,3-butadiene [1, vol.2 470], tetra-aza-1,3-butadiene [1, vol.2], penta-azadienes [471], azomethines of 2,5-diformylpyrrole [472,473], cyclic hydrazones and thiosemi-carbazones [262], dibenzotetra-aza[14]annulene [474], hetarylaminoazocompounds [8,404,475], azoazine radicals [476], Schiff bases of heterocyclic series [132,133,477], and azoleazines [132,133,478,479]. 

A number of modifications to the diazoalkane approach are possible. For instance, a number of cyclic hydrazones h2(CH2) i =NNH2... 

A ring contraction involving this reaction has been found in cyclic hydrazones, hydrazides, and triazenes. 

Pyridazine, one of three possible isomeric diazines, can be regarded as a cyclic hydrazone and the mutual proximity of the nitrogen atoms is reflected in somewhat different properties and reactions when compared to those of pyrimidine and pyrazine. 

Compound (1) and its enantiomer provide a variation on the same theme of stereospecific reductive amination. In this case, reduction of a chiral cyclic hydrazone (derived from an a-keto acid and (1)) with Aluminum Amalgam in wet DME proceeds with high stereoselectivity. Reductive cleavage of the N-N bond and ester hydrolysis complete the procedure, which produces a-amino acids with high optical purity (eq 4). The source of chirality is recovered by conversion of the resulting indoline-2-methanol back into (1). ... 

A reduction route similar to that of phenylhydrazones [229] seems to be rather general for azomethine derivatives of hydrazine [229] as it s followed by cyclic and acylic phenylhydrazones, semicarbazones, azines, cyclic hydrazones, and acylated cyclic and acyclic hydrazones [231] under pro tic conditions in DMF, acylated hydrazones of aromatic aldehydes are reduced with saturation of the C=N bond and cleavage of the N-N bond at a more negative potential [232]. The suggestion that the cleavage of the N-N bond precedes the saturation of the azomethine bond is also an essential part of the interpretation of many of the ring contractions of heterocyclic compounds (Chapter 18). 

Pyrolysis of cyclic hydrazones from 1-hydrazinophthalazine has been investigated and the work of Druey and Ringier from the early 1950s has been corrected and extended (Scheme 4). The 5- and... 

The reaction of the cyclic carbonate 306 with hydrazine hydrochloride and Pr 2NEt in ethanol at reflux produced the cyclic hydrazone 307 via partial, regioselective hydrazinolysis of 306 followed by intramolecular condensation of the resultant hydrazide with the unmasked hemiacetal group (Equation 51) <2005SL2607>. 

A five-step synthesis of ethyl ester of cyclic hydrazonic acid 314 used in the synthesis of natural products has been described [94JCA(CC)1867]. The condensation of methoxybutenone with EtCOaCN (t-BuOK, THF, —78°C) is completed with the formation of ketoester 310 in 72% yield. The addition of methanol to the latter (Triton B, MeOH, room temperature, 88%) and the reduction with NaBH4 (EtOH, —78°C) leads to the alcohol 312, yield 90%. The dianion of 312 (LDA, THF, —78°C) reacts with f-butylazodicarboxylate (t-Bu02C—N=N—CO2BU-O to form adduct 313, the treatment of which with trifluoroacetic acid affords the ester 314 in 55% yield [94JCA(CC)1867]. 

The reaction of D-glucose phenylhydrazone with glacial acetic acid has been examined iV-fructosyl-A -glucosylphenylhydrazine was formed at 30 °C, whereas 1,2-dideoxy-l -phenylimino-2-phenylhydrazono-D-ara6//io-hexose was obtained after brief treatment at 100 2-(D-arfli //jo-Tetrahydroxybutyl)quinoxaline was also formed. The acetolysis of the 2,3,4,6-tetra-0-acetyl-j8-D-glucopyranosyl 2,4-dinitrophenylhydrazine (154) yielded a mixture of acyclic and cyclic hydrazones... 

---