(Diazomethyl)dimethylphosphine Oxide – A Diazoalkane Reagent for [3+2] Cycloadditions

A safe and efficient method for the in-situ preparation of (diazomethyl)dimethylphosphine oxide – a hereto unexplored diazoalkane reagent – is developed. The method is based on the diazotization of the corresponding P(O)Me2-substituted amine (readily available in multigram quantities) in non-aqueous media. The protocol provides the target product as ca. 1.5 M CHCl3 solution which is stable at –18 C. The utility of the synthesized diazoalkane is illustrated by its [3+2] cycloaddition with electron-poor alkynes and alkenes providing the corresponding P(O)Me2-substituted pyrazoles and pyrazolines with moderate to good efficiency. In this view, the title compound represents and an important extension of medicinally relevant phosphine oxide reagents.