Phosphazines, reaction with

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. 

Studies (2, 3) have also been reported of the reaction of phosphorus trichloride with diarylamines containing p-methyl or p-chloro substituents. In every case, the expected ring-substituted derivatives of 1 and 2 were obtained after the reaction mixture was treated with water. The interaction of (V-phenyl-o-toluidine and phosphorus trichloride at 200°C also gave a reaction mixture from which the expected phosphine oxide was isolated (3). None of the corresponding spirophosphonium chloride, however, could be obtained. The failure to isolate this substance can not be explained simply by the presence of an ortho substituent in the diarylamine, since it had been previously found that a 34% yield of a spirophosphonium chloride can be obtained via the interaction of fl/-phenyl-l-naphthylamine and phosphorus trichloride (2). No dihydropheno-phosphazine derivatives at all were obtained by the interaction of di-o-tolylamine and phosphorus trichloride at 200°C (3). 

Aliphatic diazo compounds may also be used as a source for carbenes, which combine subsequently with tertiary phosphines to give phosphonium ylides. The reaction requires the presence of Cu salts, otherwise phosphazines are formed from the diazo compounds and the phosphines. 

Compounds 21 react with triphenyl phosphine to give the corresponding phosphazines. When the starting diazocompound carries a vinyl group substituted by a carbonyl function, an intramolecular Aza-Wittig reaction provides an interesting entry to CF3-substituted pyridazines 24 (Scheme 41, ref. 33). 

The authors propose the following catalytic cycle for the organophosphorus-catalyzed diaza-Wittig reaction (1) reduction ofphospholene oxide with diphenylsilane to phospholene (2) generation of the phosphazine intermediate via a reaction of phospholene with a diazo derivative (3) transformation of the phosphazine intermediate into the oxazaphosphetane intermediate and (4) loss of pyridazine 22 and regeneration of phospholene oxide (Figure 1). 

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