Ylide Aspects of Iminophosphoranes

The bis(iminophosphoranes) (143) and (144) have been obtained as shown. Electrophilic olefins and the phosphino-imines (145) gave the cyclic iminophosphoranes (146). 

Additional examples have been obtained of the change in the rate-determining step, from betaine formation to betaine decomposition, in the reactions of aromatic aldehydes with the iminophosphoranes 

The trimethylsilyliminophosphoranes (147) with tri- and tetra-fluoro-phosphoranes give the salts (148) and (149), respectively. 

Activity in this area continues at about the same level as last year, although an increasing emphasis on the physical properties of the phosphazenes is apparent. On the chemical side, several novel routes to both acyclic and cyclic phosphazenes have been developed, and the aminocyclophosphazenes remain a major source of interest. 

A general synthesis of the secondary amines RNHMe and RNHEt has been developed starting from the iminophosphoranes (181). Alkylation with methyl or ethyl iodides (all other halides gave olefins) gave the salts (182) from which secondary amines were obtained on alkaline hydrolysis. 

The iminophosphoranes (181) with imide bromides gave the amidino-phosphonium bromides (183) which, it appears from their temperature-variable n.m.r. spectra, are interesting fluxional molecules. The free energy of activation for the interconversion of (183a) and (183b) (R R = Pr R3 = Ph) is 17.2 0.9kcalmol-i. 

120 Winkler, W. Von Philipsborn, J. Stroh, W. Silham, and E. Zbiral, Chem. Comm., 1970, 1645. 

Mixtures of a-phenyliminoesters (187) and the tautomeric enamines (188) resulted from the reaction of phenyliminotriphenylphosphorane with a-keto-esters. 

Oxazoles (191) are producedwhen triphenylphosphine is treated simultaneously with an a-azidocarbonyl compound and an acyl halide. The intermediate iminophosphoranes (189) react with the acyl halide before they can react with themselves to give pyrazines. Elimination of phosphine oxide from the resulting salts may give the intermediate halo-genoimines (190), or the oxazoles may be formed via the betaines (192). 

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