Phosphathioketenes 2+2 cycloaddition

Cycloaddition phosphathioketenes, 33 332 reactions, in preparation of fluoroalicyclic derivatives, 15 327-328 reactions, of iminoboranes, 31 159-165 [2-1-2] Cycloaddition phosphaalkenes, 33 271-272 phosphathioketenes, 33 334 [2-t-l] Cycloaddition, phosphaalkenes, 33 269-271... 

Its structure as determined by an X-ray investigation is shown in Fig 21. It may be understood as a dimer of the assumed phosphathio-ketene intermediate. The cycloaddition of the phosphathioketene corresponds to the behavior of unsubstituted carbaketenes (146) and so is different from that of the phosphaketenes described earlier, while thioketenes dimerize to 1,3-dithietanes (147,148). An asymmetric retro ring cleavage can be initiated if l-thia-3-phosphetane is irradiated by a mercury lamp generating carbon disulfide and the 1,3-diphosphaallene [Eq. (78)] (117, p. 33). 

If a suitably reactive reagent for the interception is missing, a [2 + 2] cycloaddition of the phosphathioketene is observed, which takes place with the precursor and leads to the phosphathietane [Eq. (81)] (118, p. 30). 

Replacement of P=C in an unstable monomer by P-C in the dimeric form is fairly common (13.280). Similarly, P C monomers will dimerise as in Equation 13.281. The dimer may in some cases be capable of undergoing further reaction (called 2-1-2 cycloaddition or cyclotetramerisation) to form a cubane molecule (13.282). Further examples of dimerisations are provided by phosphake-tenes (13.283), phosphathioketenes (13.284) and phosphaallyl derivatives (13.285) and (13.286). 

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