Phosphaalkenes phosphorus atom reactions

The P=C bond of A5a3-phosphoranes is also accessible to a 1,3-dipolar cycloaddition reaction. The formation of 97 (Scheme 8.23), of 3,5-dihydro-1,2,4-diazaphosphole sulfide 132 from an amino(methylene)thioxophosphorane (190) and of phosphirane imine 133 from an amino(imino)alkylidenephosphorane (191) (Scheme 8.29) illustrate the chemical behavior of phosphaalkenes containing a A3a2-phosphorus atom. 

Phosphorus ylides, P=C compounds with a pentavalent phosphorus atom, can give phosphetanes as well as phosphaalkenes. By the reaction of a stabilized phosphoms ylide with activated alkenes, the phosphetane ring is formed via a zwitterionic betaine <1997HAC157>. 

Nucleophiles react with cyclopropenium 2C and diphosphirenylium salts 2Pa affording the corresponding cyclopropenes 1C and lH-diphosphirenes l Px (Scheme 14), respectively. Nucleophiles such as lithium salts also react at the dicoordinate phosphorus atom of the diphosphirenium salt 2 Pa [22b, 45], but in this case ring opening reactions occur affording the phosphaalkenes 15 rather than the thermodynamically unfavored cyclic 47r-electron ylides 19. Cleavage of... 

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