Phosphazines hydrazones

The reaction of V-aminotriphenyliminophosphoranes with aldehydes and ketones is influenced by the presence or absence of water under anhydrous conditions phosphazines (65TL1447) are formed, while trace amounts of water lead to the formation of hydrazones (64AG991) and phosphane oxide. 

Another method for the preparation of the 1,2,4,5-tetrazine system from a diazo compound was reported by Staudinger and Meyer (19HCA619). They reacted diaryldiazomethanes (321) with triethylphosphine and isolated the phosphazines (322). In moist benzene or chloroform these compounds were transformed into 3,3,6,6-tetraaryl-l,2,3,6-tetrahydro-1,2,4,5-tetrazines (323). This result was only obtained when triethylphosphine was used. The intermediate formation of hydrazones seems unlikely, since these compounds are stable and do not dimerize. A reaction which has a certain similarity to the above was reported by Merrill and Shechter (75TL4527). They obtained 3,6-diphenyl-l,4-dihydro-l,2,4,5-tetrazine (80) when the phosphazine (324) was hydrolyzed. 

The mesomeric diazo compound lOOa/lOOb, derived from diazo group transfer to the appropriate pyrazol-3-one, was irradiated for 10 h in tetrahydrofuran to give the hydrazone chelated adduct 101 as the only product (78H199) (Scheme 29). Mesomeric lOOa/lOOb reacts also with triphenylphosphine to give intermediate ( /Z)-phosphazine 102 which is extremely sensitive to water and hydrolyzes to EjZ)-hydrazone 103. 3-Hydroxy-5,5-dimethyl-cyclohex-2-enone 104 and 3-hydroxy-inden-1-one 106 readily couple with lOOa/lOOb in the presence of sodium acetate to give hydrazono derivatives 105 and 107, respectively. 

H.J. Bestmann has prepared the phosphazine of TFAE from 18 and triphenyl phosphine. This compound is hydrolyzed by ZnCl2/H20 to give the parent hydrazone 22 and it can be transformed to the corresponding tris carbonyl compound using HN02 (ref. 41). In analogy to the studies by H. Neuenhoffer, we have N-acylated 22 by acid anhydrides to obtain crude N-acylhydrazones 211 in about 50 % yield (Scheme 46). 

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