Osazones dianhydro

Another 2,3-bis(phenylhydrazone), namely, l,5 4,6-dianhydro-2,3-hexodiulose bis(phenylhydrazone) (62a), was also found to cyclize to a pyrazoline (63a) by the action of copper(II) sulfate or benzalde-hyde, which usually convert osazones into aldosuloses or osotria-zoles.65 Reduction of this bicyclic compound (63a) led to the pyrazo-lidine 64, and periodate oxidation of 63a gave the expected aldehyde 65. 

Anhydro-osazones are also obtained when osazones are refluxed with acetic acid thus, di-0-acetyl-3,6-anhydro-n-n6o-hexulose 1-iV -acetyl-phenylosazone (92) is formed, together with the dianhydro-osazone (described on p. 178), from n-aroWwo-hexulose phenylosazone (43) and boiling acetic anhydride. On deacetylation, compound (92) yields Diels anhydro-osazone (90), and (92) can be prepared from the latter by acetylation with boUing acetic anhydride. 

Dianhydro-osazones Having Pyrazole Rings.— Another dianhydro-osazone was obtained as the acetate (96) by the author and coworkers by acetylating phenylosazone (43) with boiling acetic anhydride. On de-O-acetylation with methanolic ammonia, the hexose compound (96) yields the iV-acetyl-dianhydro-osazone (97), from which (96) can be prepared by acetylation. The de-O-acetylated dianhydro-osazone (97) was... 

The structure of Percival dianhydro-osazone has been established, and Mester and Moczar have shown that dehydro-D-glucosazone has the cyclic structure (48) rather than an acyclic structure as has previously been suggested. The observed chemical shifts and coupling constants are in accord with the conformation shown (49). 

Hi) Bicycle Dianhydro-Osazones.—This third type of anhydroosazone was first prepared by Percival when deacetylating a hexulose phenyl-osazone tetraacetate with sodium hydroxide. Two enantiomeric compounds are otainable from hexose precursors, one from D-hexoses and the other from L-hexoses.166 Tricyclic structures were first assigned to these compounds, but were later revised.428 Finally, NMR data provided evidence for a chelated bicyclic structure 231 which possesses one imino proton429 These dianhydroosazones are formed from the same intermediate, 2-phenylazo-l-phenylhydrazono-l-alkenes (229) by conjugate elimination to give 230, followed by nucleophilic attack of 0-6 to afford the product 231 (Scheme 54). 

---