Phosphazines —

Solladie-Cavallo has recently reported a two-step asymmetric synthesis of dis-ubstituted N-tosylaziridines from (R,R,R,Ss)-(-)-sulfonium salt 2 (derived from Eliel s oxathiane see Section 1.2.1.1) and N-tosyl imines with use of phosphazine base (EtP2) to generate the ylide (Scheme 1.42) [67], Although the diastereoselectiv-ity was highly substrate-dependent, the enantioselectivities obtained were very high (98.7-99.9%). The chiral auxiliary, although used in stoichiometric quantities, could be isolated and reused, but the practicality and scope of this procedure is limited by the use of the strong - as well as expensive and sensitive - phospha-zene base. 

Phi = NTs ([N-(p-toluenesulfonyl)iminio]phe-nyliodinane) 79 phomactin A 307 (+)-phonomactin 277 ( )-phoracantholide 299 phosphazene base 3 f. phosphazine base 31 phospholene epoxide 243 phosphoramidite 261 phosphoramidite ligand 247 piperidinephosphonate 103 pipermethystine 302 P K 177... 

The synthesis of pyrrolo[3,4-c]pyridazines 20 is achieved by intramolecular aza-Wittig reactions of the phosphazines 19 <95JHC1457>. 

The pyrazole phosphazine ligand, hexakis(3,5-dimethylpyrazolyl)cyclotriphosphazene (16) forms a dizinc complex, that has been structurally characterized, and the analogous copper zinc complex.158 Two ZnCl2 units are coordinated, one distorted tetrahedral and one distorted trigonal-bipyramidal, separated by 7.51 A. Cu1 and ZnCl2 can also be coordinated giving a heteronuclear compound with a Zn Cu separation of 6.798 A. 

DBU, phosphazine bases, Na2C03, K2C03, Cs2C03, variety of solvents/temperatures NR... 

In addition to the types of structures shown thus far, there are several others that are both interesting and important. One such type of structure contains unsaturated rings. Because R-C=N is called a nitrile, compounds containing the -P=N group were originally called phosphonitriles. An unstable molecule having the formula N-PH2 is known as phosphazine. Although this molecule is unstable,... 

By carrying out reactions of the types shown here, a very large number of phosphazines have been prepared. In addition to synthetic work, a great deal of theoretical work has been done to elucidate the bonding in phosphazines. 

What types of reactions would the nitrogen atoms in a phosphazine ring undergo ... 

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. 

Similarly, a pyrazole synthesis occurs on addition of diazoacetic ester to diacylimine thereby, the diazo group of the intermediate adduct is converted with triphenylphosphane into a phosphazine, which gives pyrazole as described above (68TL4371). 

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. 

On treatment with base, the 3-p-tosylhydrazone of benzo[6]thio-phene-2,3-quinone affords 3 - diazobenzo[6]thiophen - 2 - one (259) which reacts with triaminophosphines to give the o-quinone triamino-phosphazines (260 NR2 = NMe2, morpholino, or piperidino),627 and with phenols to give azo dyes.628... 

Triphenylphosphinimines (476) react with DMAD to give phosphoranes of the type 478 [Eq. (70)].278-281 It has been reported that a phosphazine, such as 479, reacts with DMAD to give the adduct 480, which is transformed to the pyrazole 481 on heating [Eq. (71)].278... 

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). 

A hybrid borazine-phosphazine ring system has been found in... 

Phosphazines are compounds containing repeated PX2N units. For example, the reaction nPCl5 + nNH4Cl (NPCl2)n + 4nHCl... 

Aufgrund der Ahnlichkeit ihrer Herstellung werden Phosphanimide und Phosphazine nicht getrennt behandelt (vgl. Bd. XII/1, S. 175, 180), sondem gemeinsam dargestellt Phosphazine sind letztlich nur als spezifisch substituierte Phosphanimide anzusehen. 

Uber Aminophosphonium-Salze sind auch Phosphazine zuganglich (s. Bd. XII/1, S. 181). Hydrazino-phosphonium-Salze setzen sich in guten Ausbeuten mit Aldehyden oder Keto-nen zu Phosphazinen urn699 ... 

Zur Entfernung des mitentstandenen Wassers wird der Reaktionsmischung Molsieb (4 A) zugesetzt, um die Hydrolyse der empfindlichen Phosphazine zu vcrhindern. Aromatische Aldehyde und Ketonen reagieren gut in diesem Sinne. 

G. Singh u. H. Zimmer, Tetiary Phosphinimines and Phosphazines, Organometallic Reviews 2, 279 (1967). 

C. Triptycenes. Extension of the common syntheses of phosphazines to the use of trisubstituted aromatic amines as starting materials produces triptycene derivatives (54) (69AG(E)987). The compounds are also available from phenophosphazines in a two-step process, which is claimed to give higher yields (78CB1798). 

C. W. Allen, Organophosphorus Chem. 1992,23,313 (298 references) phosphazine complexes of transition metals. 

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