Phosphetane Oxides as Redox Cycling Catalysts in the Catalytic Wittig Reaction at Room Temperature

Recently, phosphorus redox cycling gained significant importance for a number of transformations originally requiring the use of stoichiometric amounts of phosphorus reagents. While these methodologies have several benefits, high catalyst loadings (≥10 mol%) and harsh reaction conditions (T≥100 °C) often limit their versatility and applicability. Herein, we report differently substituted phosphetane oxides as efficient catalysts for the catalytic Wittig reaction. The phosphetane scaffold is easy to modify and a number of catalysts can be obtained in a simple two step synthesis. The activity in the Wittig reaction significantly surpasses previously reported phospholane-based catalysts and the reaction can be conducted with catalyst loadings as low as 1.0 mol% even at room temperature. Furthermore, a Bronsted acid additive is no longer required to achieve high yields at these mild conditions. A methyl-substituted phosphetane oxide was employed to synthesize 25 different alkenes with yields up to 97%. The me...