(Digital Presentation) Electrochemical Dehydrogenative C–P Bond Formation for the Synthesis of Phosphacycles Using DABCO As a Mediator

Abstract

Phosphole oxide-containing π-conjugated molecules have been attracting attention due to their electron acceptability and thermal and chemical stability, and have been used as an important motif for organic functional materials. Among them, diarylphosphole oxide (DPO) is a key motif in the design of phosphole-containing organic functional materials. Recently, intramolecular cyclization of biarylphosphine oxides (BPOs) has received attention as a straightforward way leading to DPOs. BPOs are readily available and easy to handle starting substrates. Although several efficient methods have been reported for synthesizing DPOs with this protocol, these methods require transition metal catalysts, strong acids or excess amounts of acid. Therefore, the development of a transition metal-free and environmentally benign synthetic methodology for synthesizing DPOs is highly desirable.To overcome the situation, we developed the first electrochemical synthesis of DPOs from BPOs via a dehydrogenative C–P bond formation. The protocol does not use a transition metal mediator and instead uses readily available and inexpensive DABCO as an organic hydrogen atom transfer (HAT) mediator. In the presence of DABCO, the desired C–P bond formation proceeded smoothly and a wide variety of DPOs could be obtained. This method can also be applied to the synthesis of six-membered phosphacycles. Several control experiments were carried out, and the results suggest that a phosphinyl radical was generated in situ and the reaction would proceed via a radical pathway. Figure 1