A-phosphorus stabilized imines

Table 5 Reaction of a-Phosphorus-stabilized Imine Anions with Carbonyl Compounds (Scheme 13)...

The phosphonitrilic halides are weaker bases than are some related nonaromatic compounds, just as pyridine is a weaker base than piperidine. The bond type in the phosphonitrilic series is probably the same as in the phosphine-imines RaPrNR (80, 81) the stability of these compounds, too, increases with the electronegativity of the substituents on the phosphorus. Tetraphenylphosphine-imine is one of the most stable of these compounds, and forms a hydrochloride. Its base strength is therefore greater than those of the phosphonitrilic halides, presumably because the opportunities for electronic delocalization are less. The Af-ethyl ester of the trimeric phosphonitrilic acid, which has a cyclic structure, but in which resonance of the same type as in the phosphonitrilic halides cannot occur, also forms a hydrochloride ( 1). It is, therefore, a comparatively strong base, in spite of the inductive effect of the two oxygen atoms on the phosphorus. The extreme weakness of the phosphonitrilic halides as bases cannot therefore be wholly due to the inductive effect of the halogens. 

As well as the Bingel reaction and its modifications some more reactions that involve the addition-elimination mechanism have been discovered. 1,2-Methano-[60]fullerenes are obtainable in good yields by reaction with phosphorus- [44] or sulfur-ylides [45,46] or by fluorine-ion-mediated reaction with silylated nucleophiles [47]. The reaction with ylides requires stabilized sulfur or phosphorus ylides (Scheme 3.9). As well as representing a new route to l,2-methano[60]fullerenes, the synthesis of methanofullerenes with a formyl group at the bridgehead-carbon is possible. This formyl-group can be easily transformed into imines with various aromatic amines. 

---