Reactivity of 1-hydro-5-carbaphosphatrane based on tautomerization between pentavalent phosphorane and trivalent cyclic phosphonite

The reaction behavior of 1-hydro-5-carbaphosphatrane (1 a) was examined. Treatment of 1 a with oxidants such as 3-chloroperoxybenzoic acid (mCPBA) and tBuOCl gave cyclic phosphonate 2 and 1-chloro-5-carbaphosphatrane (4), respectively, via cyclic phosphonite 3, a tautomer of 1 a. Compound 4 was readily hydrolyzed to afford 2. Compound 1 a was also sulfurized via 3 by elemental sulfur to afford cyclic thioxophosphonate 5, which was also obtained by reactions in the presence of bases. Treatment of 1 a with bases also proceeded through 3 to give an equilibrium mixture of the corresponding phenoxide anion 10 and the phosphoranide anion 9, which was quenched with MeI to afford a mixture of 11 and 1-methyl-5-carbaphosphatrane (1 b). Such reactivities are typical for neutral phosphoranes. Theoretical investigations of these reactivities were also performed.