Phosphazines salts

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. 

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. 

Without additional reagents Hydrazinophosphonium salts from diazo oxides via phosphazines... 

Imidinophosphoranes Phosphazines Phosphazinium salts Phosphorus cyanimides... 

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