Ylides Phosphoranes

Another example of ylide-phosphorane equilibrium is found in the reaction of trimethyl phosphite with acetylenic ketones, in the presence of phenol as trapping reagent216 (Scheme 42). Here, too, the 155 156 ratio depends on the nature of the solvents, being 37 63 in CH2C12 and 74.5 25.5 in CC14. 

Electrochemistry of ylides, phosphoranes and phosphonium salts TABLE 2. Cyclic voltammetric features of probases... 

The synthesis of phosphonium ylides by reaction of ( )-2-benzylideneoxazolidine-4,5-dione with methylenetriphenylphosphoranes has been reported12 these ylide phosphoranes have the structure PhCH2CONHCOCOCR=PPh3 with R = COOMe, COOEt and COPh. 

Chemical Model Showing Three Phenomena Phosphorane--Ylide, Ylide— Phosphorane, and Phosphorane Ylide... 

Calculations have revealed that the proazaphosphatrane bases are approximately equal in thermodynamic basicity to the Schwesinger P2 phosphazene bases (Table 2.14). The RHF/ 6-3IG calculations of proton affinities indicate that phosphazene (Z = NH) and phosphorus ylide (phosphorane, Z = CH2) counterparts (146 and 145) are stronger than the parent Verkade superbase 139. Higher basicity is associated with the higher degree of delocalization of the positive charge in the protonated iminophosphoranes and phosphorus ylides as a result of the more electropositive character of phosphorus atom [67]. On the other hand, phosphoms oxides 147 and 150 are weaker than 139, but still above the superbasicity borderline. The strained polycycles 138, 149 and 148, as representatives of superbases... 

Phosphine chalcogenides Phosphonium salts Ylides (phosphoranes)... 

---