Group 15 elements phosphaalkenes

The class of phosphaalkenes with isolated P=C double bonds was first synthes ized by Becker.33 His synthetic strategy starting from trimethylsilylphosphines and acyl chlorides is still the most versatile (Protocol 3). The principle is based on the easily achievable, 1,3-silatropic migration of a silyl group bonded to phosphorus to a doubly bonded element such as nitrogen, oxygen, or sulfur. The process is favoured energetically by the construction of the P=C double bond with concomitant formation of a very stable silicon-element bond. 

The scope of three-membered rings with two heteroatoms of heavier group 15 elements includes essentially heterocyclopropanes and heterocyclopropenes with two phosphorus atoms. This chapter also covers bicyclic and polycyclic molecules containing the structural motif of the rings under discussion. Such species frequently result from transformations of phosphaalkenes or oligomers. Monocyclic diphosphirane and diphosphirene derivatives are synthesized from acyclic precursors with a P-C-P linkage or alternatively via [2-1-1] cycloadditions. A few examples... 

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