Reduction of phosphine oxides to the corresponding phosphines represents the most straightforward method to prepare these valuable reagents. However, existing methods to reduce phosphine oxides suffer from inadequate chemoselectivity due to the strength of the P=O bond and/or poor atom economy. Herein, we report the discovery of the most powerful chemoselective reductant for this transformation to date, 1,3-diphenyl-disiloxane (DPDS). Additive-free DPDS selectively reduces both secondary and tertiary phosphine oxides with retention of configuration even in the presence of aldehyde, nitro, ester, α,β-unsaturated carbonyls, azocarboxylates, and cyano functional groups. Arrhenius analysis indicates that the activation barrier for reduction by DPDS is significantly lower than any previously calculated silane reduction system. Inclusion of a catalytic Brønsted acid further reduced the activation barrier and led to the first silane-mediated reduction of acyclic phosphine oxides at room temperature.
Bibliographical noteFunding Information:
This work was supported by startup funds from the University of Minnesota to C.C.A. J.A.B. thanks the National Science Foundation (pre-doctoral fellowship, GRFP-ID: 00039202), the Uni- versity of Minnesota College of Pharmacy (Bighley fellowship), and the University of Minnesota Graduate College (doctoral dissertation fellowship) for financial support. C.G.E. thanks the National Institutes of Health Chemistry-Biology Interface training grant (T32-GM008700) for financial support.
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- chemoselective methods
- phosphine oxides
- silane reductions
- synthetic methods