Efficient one-pot synthesis of secondary cyclic phosphanes with easy regeneration of the phosphorus-donor reagent used

Phosphanes: No pain, all gain. A regenerable phosphorus donor is the key to an efficient and economic one-pot synthesis of five- and six-membered secondary cyclic phosphanes. The reaction, at room temperature, of 1 with 1 equivalent of bis(Grignard reagent) 2 followed by treatment with aqueous acid gives cyclic phosphanes 3 in 70-80% yield and the new compound 4. Simply treating 4 with PCl3 quantitatively regenerates the starting reagent 1, which can be reused without further purification.