Formation of the PC Double Bond

Because the main routes to phosphaalkene formation have already been published in diverse review articles (8-11), this report can be restricted to a short survey of the general principles. 

In analogy to the chemistry of olefins, 1,2-elimination with suitable organyl phosphanes has proved valid. Those molecules with substituents showing inverse polarities may give thermodynamically favored leaving molecules XY [Eq. (2)]. The formation of XY is initiated thermally by bases or metals (12-21). 

It is possible in many cases to create PC double bonds via condensation in separations of halosilane, siloxane (22), or even water (23a-c). Likewise, formaldehyde or benzaldehyde reacts with 2,4,6-fri-t-butyl-phenylphosphane, forming the phosphaalkene, supported by dehydration agents such as P4Ol0 or CaO/CaCl2 [Eq. (3)]. This method is excep- 

Another well-established process available for the preparation of PC double bonds is related to the easy migration of phosphorus-bonded silyl functions toward an a-positioned, doubly bonded element such as N, O, or S [Eq. (4)]. By this silatropic movement the double bond is 

Condensations followed by silyl migrations are achieved easily with carbon acid chlorides, imid chlorides (7, 26-28), and adequate derivatives of carbonic acid such as phosgene [Eq. (5a)] and isocyanide dichlorides [Eq. (5b)] (29-31). After the primary condensation to the 

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