[3 + 2] Cycloaddition of Diazomethane Derivatives to Perfluoro-2-phosphapropene

Perfluoro-2-phosphapropene (1) reacts with diazo compounds R(H)C=N-2 (R = H (2a), Ph (2b), CO2Et (2c), Me3Si (2d)) at low temperatures regioselectively yielding via 1,3-H shift the novel 1,2,3-diazaphospholes 4a-d. The mesomerically stabilized compounds 4b and 4c were characterized by NMR spectroscopy and single crystal X-ray diffraction studies. Using diphenyldiazomethane 5 as partner for 1, the cycloaddition is spontaneously followed by N-2 elimination to give the crystalline phosphirane derivative 7. The analogous reaction of 1 with 9-diazofluorene 9 unexpectedly leads to the so-far unknown 1,2-diphosphinane compound 11. Quantum chemical calculations for the gas phase on DFT and RHF level prove that for both the perhydro- and the perfluoro-2-phosphapropene the [3 + 2]-cycloaddition is kinetically determined and that, due to high stability of the products, the thermodynamic equilibrium with the slightly more stable isomers is not accessible.