Silanes as Reagents for the Deoxygenation of Tertiary Phosphine Oxides – A Case Study for the Deoxygenation of 5-Membered Cyclic Phosphine Oxides

The possibilities for the deoxygenation of 3-methyl-1-phenyl-3-phospholene 1-oxide were investigated using different silanes. Cl3SiH and PhSiH3 were efficient, but they have disadvantages regarding user-friendliness and price, respectively. Tetramethyldisiloxane and polymethylhydrosiloxane that are cheap and user-friendly, but are of lower reactivity could be applied at 110 °C in toluene solution, without the use of any catalyst successfully. Then, the deoxygenation was extended to other 1-phenylphospholene oxides and phospholane oxides. The cyclic phosphines useful as ligands in transition metal complexes were identified as their sulfides and boranes. The catalyst-free method elaborated seems to be of more general value.